1 \input texinfo @c -*-texinfo-*-
2 @comment ========================================================
3 @comment %**start of header
4 @setfilename autoconf.info
9 @setcontentsaftertitlepage
13 @c @ovar(ARG, DEFAULT)
14 @c -------------------
15 @c The ARG is an optional argument. To be used for macro arguments in
16 @c their documentation (@defmac).
18 @r{[}@var{\varname\}@r{]}
21 @c @dvar(ARG, DEFAULT)
22 @c -------------------
23 @c The ARG is an optional argument, defaulting to DEFAULT. To be used
24 @c for macro arguments in their documentation (@defmac).
25 @macro dvar{varname, default}
26 @r{[}@var{\varname\} = @samp{\default\}@r{]}
29 @c Handling the indexes with Texinfo yields several different problems.
31 @c Because we want to drop out the AC_ part of the macro names in the
32 @c printed manual, but not in the other outputs, we need a layer above
33 @c the usual @acindex{} etc. That's why we first define indexes such as
34 @c acx meant to become the macro @acindex. First of all, using ``ac_''
35 @c does not work with makeinfo, and using ``ac1'' doesn't work with TeX.
36 @c So use something more regular ``acx''. Then you finish with a printed
37 @c index saying ``index is not existent''. Of course: you ought to use
38 @c two letters :( So you use capitals.
40 @c Second, when defining a macro in the TeX world, following spaces are
41 @c eaten. But then, since we embed @acxindex commands that use the end
42 @c of line as an end marker, the whole things wrecks itself. So make
43 @c sure you do *force* an additional end of line, add a ``@c''.
45 @c Finally, you might want to get rid of TeX expansion, using --expand
46 @c with texi2dvi. But then you wake up an old problem: we use macros
47 @c in @defmac etc. where TeX does perform the expansion, but not makeinfo.
49 @c Define an environment variable index.
51 @c Define an output variable index.
53 @c Define a CPP variable index.
55 @c Define an Autoconf macro index that @defmac doesn't write to.
57 @c Define an Autotest macro index that @defmac doesn't write to.
59 @c Define an M4sugar macro index that @defmac doesn't write to.
61 @c Define an index for *foreign* programs: `mv' etc. Used for the
62 @c portability sections and so on.
67 @c Shall we factor AC_ out of the Autoconf macro index etc.?
74 @c Registering an AC_\MACRO\.
81 @ifclear shortindexflag
89 @c Registering an AH_\MACRO\.
97 @c Registering an AS_\MACRO\.
104 @ifclear shortindexflag
105 @macro asindex{macro}
112 @c Registering an AT_\MACRO\.
113 @ifset shortindexflag
114 @macro atindex{macro}
119 @ifclear shortindexflag
120 @macro atindex{macro}
127 @c Registering an AU_\MACRO\.
128 @macro auindex{macro}
135 @c Indexing a header.
136 @macro hdrindex{macro}
137 @prindex @file{\macro\}
143 @c Registering an m4_\MACRO\.
144 @ifset shortindexflag
145 @macro msindex{macro}
150 @ifclear shortindexflag
151 @macro msindex{macro}
157 @c Define an index for functions: `alloca' etc. Used for the
158 @c portability sections and so on. We can't use `fn' (aka `fnindex),
159 @c since `@defmac' goes into it => we'd get all the macros too.
161 @c FIXME: Aaarg! It seems there are too many indices for TeX :(
163 @c ! No room for a new @write .
164 @c l.112 @defcodeindex fu
166 @c so don't define yet another one :( Just put some tags before each
167 @c @prindex which is actually a @funindex.
172 @c @c Put the programs and functions into their own index.
173 @c @syncodeindex fu pr
175 @comment %**end of header
176 @comment ========================================================
180 This manual is for @acronym{GNU} Autoconf
181 (version @value{VERSION}, @value{UPDATED}),
182 a package for creating scripts to configure source code packages using
183 templates and an M4 macro package.
185 Copyright @copyright{} 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000,
186 2001, 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
189 Permission is granted to copy, distribute and/or modify this document
190 under the terms of the @acronym{GNU} Free Documentation License,
191 Version 1.2 or any later version published by the Free Software
192 Foundation; with no Invariant Sections, with the Front-Cover texts
193 being ``A @acronym{GNU} Manual,'' and with the Back-Cover Texts as in
194 (a) below. A copy of the license is included in the section entitled
195 ``@acronym{GNU} Free Documentation License.''
197 (a) The FSF's Back-Cover Text is: ``You have freedom to copy and
198 modify this @acronym{GNU} Manual, like @acronym{GNU} software. Copies
199 published by the Free Software Foundation raise funds for
200 @acronym{GNU} development.''
206 @dircategory Software development
208 * Autoconf: (autoconf). Create source code configuration scripts.
211 @dircategory Individual utilities
213 * autoscan: (autoconf)autoscan Invocation.
214 Semi-automatic @file{configure.ac} writing
215 * ifnames: (autoconf)ifnames Invocation. Listing conditionals in source.
216 * autoconf-invocation: (autoconf)autoconf Invocation.
217 How to create configuration scripts
218 * autoreconf: (autoconf)autoreconf Invocation.
219 Remaking multiple @command{configure} scripts
220 * autoheader: (autoconf)autoheader Invocation.
221 How to create configuration templates
222 * autom4te: (autoconf)autom4te Invocation.
223 The Autoconf executables backbone
224 * configure: (autoconf)configure Invocation. Configuring a package.
225 * autoupdate: (autoconf)autoupdate Invocation.
226 Automatic update of @file{configure.ac}
227 * config.status: (autoconf)config.status Invocation. Recreating configurations.
228 * testsuite: (autoconf)testsuite Invocation. Running an Autotest test suite.
233 @subtitle Creating Automatic Configuration Scripts
234 @subtitle for version @value{VERSION}, @value{UPDATED}
235 @author David MacKenzie
237 @author Akim Demaille
239 @vskip 0pt plus 1filll
252 @c The master menu, created with texinfo-master-menu, goes here.
255 * Introduction:: Autoconf's purpose, strengths, and weaknesses
256 * The GNU Build System:: A set of tools for portable software packages
257 * Making configure Scripts:: How to organize and produce Autoconf scripts
258 * Setup:: Initialization and output
259 * Existing Tests:: Macros that check for particular features
260 * Writing Tests:: How to write new feature checks
261 * Results:: What to do with results from feature checks
262 * Programming in M4:: Layers on top of which Autoconf is written
263 * Writing Autoconf Macros:: Adding new macros to Autoconf
264 * Portable Shell:: Shell script portability pitfalls
265 * Portable Make:: Makefile portability pitfalls
266 * Portable C and C++:: C and C++ portability pitfalls
267 * Manual Configuration:: Selecting features that can't be guessed
268 * Site Configuration:: Local defaults for @command{configure}
269 * Running configure Scripts:: How to use the Autoconf output
270 * config.status Invocation:: Recreating a configuration
271 * Obsolete Constructs:: Kept for backward compatibility
272 * Using Autotest:: Creating portable test suites
273 * FAQ:: Frequent Autoconf Questions, with answers
274 * History:: History of Autoconf
275 * Copying This Manual:: How to make copies of this manual
276 * Indices:: Indices of symbols, concepts, etc.
279 --- The Detailed Node Listing ---
281 The @acronym{GNU} Build System
283 * Automake:: Escaping makefile hell
284 * Gnulib:: The @acronym{GNU} portability library
285 * Libtool:: Building libraries portably
286 * Pointers:: More info on the @acronym{GNU} build system
288 Making @command{configure} Scripts
290 * Writing Autoconf Input:: What to put in an Autoconf input file
291 * autoscan Invocation:: Semi-automatic @file{configure.ac} writing
292 * ifnames Invocation:: Listing the conditionals in source code
293 * autoconf Invocation:: How to create configuration scripts
294 * autoreconf Invocation:: Remaking multiple @command{configure} scripts
296 Writing @file{configure.ac}
298 * Shell Script Compiler:: Autoconf as solution of a problem
299 * Autoconf Language:: Programming in Autoconf
300 * Autoconf Input Layout:: Standard organization of @file{configure.ac}
302 Initialization and Output Files
304 * Initializing configure:: Option processing etc.
305 * Notices:: Copyright, version numbers in @command{configure}
306 * Input:: Where Autoconf should find files
307 * Output:: Outputting results from the configuration
308 * Configuration Actions:: Preparing the output based on results
309 * Configuration Files:: Creating output files
310 * Makefile Substitutions:: Using output variables in makefiles
311 * Configuration Headers:: Creating a configuration header file
312 * Configuration Commands:: Running arbitrary instantiation commands
313 * Configuration Links:: Links depending on the configuration
314 * Subdirectories:: Configuring independent packages together
315 * Default Prefix:: Changing the default installation prefix
317 Substitutions in Makefiles
319 * Preset Output Variables:: Output variables that are always set
320 * Installation Directory Variables:: Other preset output variables
321 * Changed Directory Variables:: Warnings about @file{datarootdir}
322 * Build Directories:: Supporting multiple concurrent compiles
323 * Automatic Remaking:: Makefile rules for configuring
325 Configuration Header Files
327 * Header Templates:: Input for the configuration headers
328 * autoheader Invocation:: How to create configuration templates
329 * Autoheader Macros:: How to specify CPP templates
333 * Common Behavior:: Macros' standard schemes
334 * Alternative Programs:: Selecting between alternative programs
335 * Files:: Checking for the existence of files
336 * Libraries:: Library archives that might be missing
337 * Library Functions:: C library functions that might be missing
338 * Header Files:: Header files that might be missing
339 * Declarations:: Declarations that may be missing
340 * Structures:: Structures or members that might be missing
341 * Types:: Types that might be missing
342 * Compilers and Preprocessors:: Checking for compiling programs
343 * System Services:: Operating system services
344 * Posix Variants:: Special kludges for specific Posix variants
345 * Erlang Libraries:: Checking for the existence of Erlang libraries
349 * Standard Symbols:: Symbols defined by the macros
350 * Default Includes:: Includes used by the generic macros
354 * Particular Programs:: Special handling to find certain programs
355 * Generic Programs:: How to find other programs
359 * Function Portability:: Pitfalls with usual functions
360 * Particular Functions:: Special handling to find certain functions
361 * Generic Functions:: How to find other functions
365 * Header Portability:: Collected knowledge on common headers
366 * Particular Headers:: Special handling to find certain headers
367 * Generic Headers:: How to find other headers
371 * Particular Declarations:: Macros to check for certain declarations
372 * Generic Declarations:: How to find other declarations
376 * Particular Structures:: Macros to check for certain structure members
377 * Generic Structures:: How to find other structure members
381 * Particular Types:: Special handling to find certain types
382 * Generic Types:: How to find other types
384 Compilers and Preprocessors
386 * Specific Compiler Characteristics:: Some portability issues
387 * Generic Compiler Characteristics:: Language independent tests and features
388 * C Compiler:: Checking its characteristics
389 * C++ Compiler:: Likewise
390 * Objective C Compiler:: Likewise
391 * Erlang Compiler and Interpreter:: Likewise
392 * Fortran Compiler:: Likewise
396 * Language Choice:: Selecting which language to use for testing
397 * Writing Test Programs:: Forging source files for compilers
398 * Running the Preprocessor:: Detecting preprocessor symbols
399 * Running the Compiler:: Detecting language or header features
400 * Running the Linker:: Detecting library features
401 * Runtime:: Testing for runtime features
402 * Systemology:: A zoology of operating systems
403 * Multiple Cases:: Tests for several possible values
405 Writing Test Programs
407 * Guidelines:: General rules for writing test programs
408 * Test Functions:: Avoiding pitfalls in test programs
409 * Generating Sources:: Source program boilerplate
413 * Defining Symbols:: Defining C preprocessor symbols
414 * Setting Output Variables:: Replacing variables in output files
415 * Special Chars in Variables:: Characters to beware of in variables
416 * Caching Results:: Speeding up subsequent @command{configure} runs
417 * Printing Messages:: Notifying @command{configure} users
421 * Cache Variable Names:: Shell variables used in caches
422 * Cache Files:: Files @command{configure} uses for caching
423 * Cache Checkpointing:: Loading and saving the cache file
427 * M4 Quotation:: Protecting macros from unwanted expansion
428 * Using autom4te:: The Autoconf executables backbone
429 * Programming in M4sugar:: Convenient pure M4 macros
430 * Programming in M4sh:: Common shell Constructs
431 * File Descriptor Macros:: File descriptor macros for input and output
435 * Active Characters:: Characters that change the behavior of M4
436 * One Macro Call:: Quotation and one macro call
437 * Quotation and Nested Macros:: Macros calling macros
438 * Changequote is Evil:: Worse than INTERCAL: M4 + changequote
439 * Quadrigraphs:: Another way to escape special characters
440 * Quotation Rule Of Thumb:: One parenthesis, one quote
442 Using @command{autom4te}
444 * autom4te Invocation:: A @acronym{GNU} M4 wrapper
445 * Customizing autom4te:: Customizing the Autoconf package
447 Programming in M4sugar
449 * Redefined M4 Macros:: M4 builtins changed in M4sugar
450 * Looping constructs:: Iteration in M4
451 * Evaluation Macros:: More quotation and evaluation control
452 * Text processing Macros:: String manipulation in M4
453 * Forbidden Patterns:: Catching unexpanded macros
455 Writing Autoconf Macros
457 * Macro Definitions:: Basic format of an Autoconf macro
458 * Macro Names:: What to call your new macros
459 * Reporting Messages:: Notifying @command{autoconf} users
460 * Dependencies Between Macros:: What to do when macros depend on other macros
461 * Obsoleting Macros:: Warning about old ways of doing things
462 * Coding Style:: Writing Autoconf macros @`a la Autoconf
464 Dependencies Between Macros
466 * Prerequisite Macros:: Ensuring required information
467 * Suggested Ordering:: Warning about possible ordering problems
468 * One-Shot Macros:: Ensuring a macro is called only once
470 Portable Shell Programming
472 * Shellology:: A zoology of shells
473 * Here-Documents:: Quirks and tricks
474 * File Descriptors:: FDs and redirections
475 * File System Conventions:: File names
476 * Shell Pattern Matching:: Pattern matching
477 * Shell Substitutions:: Variable and command expansions
478 * Assignments:: Varying side effects of assignments
479 * Parentheses:: Parentheses in shell scripts
480 * Slashes:: Slashes in shell scripts
481 * Special Shell Variables:: Variables you should not change
482 * Limitations of Builtins:: Portable use of not so portable /bin/sh
483 * Limitations of Usual Tools:: Portable use of portable tools
485 Portable Make Programming
487 * $< in Ordinary Make Rules:: $< in ordinary rules
488 * Failure in Make Rules:: Failing portably in rules
489 * Special Chars in Names:: Special Characters in Macro Names
490 * Backslash-Newline-Newline:: Empty last lines in macro definitions
491 * Backslash-Newline Comments:: Spanning comments across line boundaries
492 * Long Lines in Makefiles:: Line length limitations
493 * Macros and Submakes:: @code{make macro=value} and submakes
494 * The Make Macro MAKEFLAGS:: @code{$(MAKEFLAGS)} portability issues
495 * The Make Macro SHELL:: @code{$(SHELL)} portability issues
496 * Comments in Make Rules:: Other problems with Make comments
497 * obj/ and Make:: Don't name a subdirectory @file{obj}
498 * make -k Status:: Exit status of @samp{make -k}
499 * VPATH and Make:: @code{VPATH} woes
500 * Single Suffix Rules:: Single suffix rules and separated dependencies
501 * Timestamps and Make:: Subsecond timestamp resolution
503 @code{VPATH} and Make
505 * VPATH and Double-colon:: Problems with @samp{::} on ancient hosts
506 * $< in Explicit Rules:: @code{$<} does not work in ordinary rules
507 * Automatic Rule Rewriting:: @code{VPATH} goes wild on Solaris
508 * Tru64 Directory Magic:: @command{mkdir} goes wild on Tru64
509 * Make Target Lookup:: More details about @code{VPATH} lookup
511 Portable C and C++ Programming
513 * Varieties of Unportability:: How to make your programs unportable
514 * Integer Overflow:: When integers get too large
515 * Null Pointers:: Properties of null pointers
516 * Buffer Overruns:: Subscript errors and the like
517 * Volatile Objects:: @code{volatile} and signals
518 * Floating Point Portability:: Portable floating-point arithmetic
519 * Exiting Portably:: Exiting and the exit status
523 * Specifying Names:: Specifying the system type
524 * Canonicalizing:: Getting the canonical system type
525 * Using System Type:: What to do with the system type
529 * Help Formatting:: Customizing @samp{configure --help}
530 * External Software:: Working with other optional software
531 * Package Options:: Selecting optional features
532 * Pretty Help Strings:: Formatting help string
533 * Option Checking:: Controlling checking of @command{configure} options
534 * Site Details:: Configuring site details
535 * Transforming Names:: Changing program names when installing
536 * Site Defaults:: Giving @command{configure} local defaults
538 Transforming Program Names When Installing
540 * Transformation Options:: @command{configure} options to transform names
541 * Transformation Examples:: Sample uses of transforming names
542 * Transformation Rules:: Makefile uses of transforming names
544 Running @command{configure} Scripts
546 * Basic Installation:: Instructions for typical cases
547 * Compilers and Options:: Selecting compilers and optimization
548 * Multiple Architectures:: Compiling for multiple architectures at once
549 * Installation Names:: Installing in different directories
550 * Optional Features:: Selecting optional features
551 * System Type:: Specifying the system type
552 * Sharing Defaults:: Setting site-wide defaults for @command{configure}
553 * Defining Variables:: Specifying the compiler etc.
554 * configure Invocation:: Changing how @command{configure} runs
558 * Obsolete config.status Use:: Obsolete convention for @command{config.status}
559 * acconfig Header:: Additional entries in @file{config.h.in}
560 * autoupdate Invocation:: Automatic update of @file{configure.ac}
561 * Obsolete Macros:: Backward compatibility macros
562 * Autoconf 1:: Tips for upgrading your files
563 * Autoconf 2.13:: Some fresher tips
565 Upgrading From Version 1
567 * Changed File Names:: Files you might rename
568 * Changed Makefiles:: New things to put in @file{Makefile.in}
569 * Changed Macros:: Macro calls you might replace
570 * Changed Results:: Changes in how to check test results
571 * Changed Macro Writing:: Better ways to write your own macros
573 Upgrading From Version 2.13
575 * Changed Quotation:: Broken code which used to work
576 * New Macros:: Interaction with foreign macros
577 * Hosts and Cross-Compilation:: Bugward compatibility kludges
578 * AC_LIBOBJ vs LIBOBJS:: LIBOBJS is a forbidden token
579 * AC_FOO_IFELSE vs AC_TRY_FOO:: A more generic scheme for testing sources
581 Generating Test Suites with Autotest
583 * Using an Autotest Test Suite:: Autotest and the user
584 * Writing Testsuites:: Autotest macros
585 * testsuite Invocation:: Running @command{testsuite} scripts
586 * Making testsuite Scripts:: Using autom4te to create @command{testsuite}
588 Using an Autotest Test Suite
590 * testsuite Scripts:: The concepts of Autotest
591 * Autotest Logs:: Their contents
593 Frequent Autoconf Questions, with answers
595 * Distributing:: Distributing @command{configure} scripts
596 * Why GNU M4:: Why not use the standard M4?
597 * Bootstrapping:: Autoconf and @acronym{GNU} M4 require each other?
598 * Why Not Imake:: Why @acronym{GNU} uses @command{configure} instead of Imake
599 * Defining Directories:: Passing @code{datadir} to program
600 * Autom4te Cache:: What is it? Can I remove it?
601 * Present But Cannot Be Compiled:: Compiler and Preprocessor Disagree
605 * Genesis:: Prehistory and naming of @command{configure}
606 * Exodus:: The plagues of M4 and Perl
607 * Leviticus:: The priestly code of portability arrives
608 * Numbers:: Growth and contributors
609 * Deuteronomy:: Approaching the promises of easy configuration
613 * GNU Free Documentation License:: License for copying this manual
617 * Environment Variable Index:: Index of environment variables used
618 * Output Variable Index:: Index of variables set in output files
619 * Preprocessor Symbol Index:: Index of C preprocessor symbols defined
620 * Autoconf Macro Index:: Index of Autoconf macros
621 * M4 Macro Index:: Index of M4, M4sugar, and M4sh macros
622 * Autotest Macro Index:: Index of Autotest macros
623 * Program & Function Index:: Index of those with portability problems
624 * Concept Index:: General index
629 @c ============================================================= Introduction.
632 @chapter Introduction
636 A physicist, an engineer, and a computer scientist were discussing the
637 nature of God. ``Surely a Physicist,'' said the physicist, ``because
638 early in the Creation, God made Light; and you know, Maxwell's
639 equations, the dual nature of electromagnetic waves, the relativistic
640 consequences@dots{}'' ``An Engineer!,'' said the engineer, ``because
641 before making Light, God split the Chaos into Land and Water; it takes a
642 hell of an engineer to handle that big amount of mud, and orderly
643 separation of solids from liquids@dots{}'' The computer scientist
644 shouted: ``And the Chaos, where do you think it was coming from, hmm?''
648 @c (via Franc,ois Pinard)
650 Autoconf is a tool for producing shell scripts that automatically
651 configure software source code packages to adapt to many kinds of
652 Posix-like systems. The configuration scripts produced by Autoconf
653 are independent of Autoconf when they are run, so their users do not
654 need to have Autoconf.
656 The configuration scripts produced by Autoconf require no manual user
657 intervention when run; they do not normally even need an argument
658 specifying the system type. Instead, they individually test for the
659 presence of each feature that the software package they are for might need.
660 (Before each check, they print a one-line message stating what they are
661 checking for, so the user doesn't get too bored while waiting for the
662 script to finish.) As a result, they deal well with systems that are
663 hybrids or customized from the more common Posix variants. There is
664 no need to maintain files that list the features supported by each
665 release of each variant of Posix.
667 For each software package that Autoconf is used with, it creates a
668 configuration script from a template file that lists the system features
669 that the package needs or can use. After the shell code to recognize
670 and respond to a system feature has been written, Autoconf allows it to
671 be shared by many software packages that can use (or need) that feature.
672 If it later turns out that the shell code needs adjustment for some
673 reason, it needs to be changed in only one place; all of the
674 configuration scripts can be regenerated automatically to take advantage
677 The Metaconfig package is similar in purpose to Autoconf, but the
678 scripts it produces require manual user intervention, which is quite
679 inconvenient when configuring large source trees. Unlike Metaconfig
680 scripts, Autoconf scripts can support cross-compiling, if some care is
681 taken in writing them.
683 Autoconf does not solve all problems related to making portable
684 software packages---for a more complete solution, it should be used in
685 concert with other @acronym{GNU} build tools like Automake and
686 Libtool. These other tools take on jobs like the creation of a
687 portable, recursive makefile with all of the standard targets,
688 linking of shared libraries, and so on. @xref{The GNU Build System},
689 for more information.
691 Autoconf imposes some restrictions on the names of macros used with
692 @code{#if} in C programs (@pxref{Preprocessor Symbol Index}).
694 Autoconf requires @acronym{GNU} M4 version 1.4.5 or later in order to
695 generate the scripts. It uses features that some versions of M4,
696 including @acronym{GNU} M4 1.3, do not have. Autoconf works better
697 with @acronym{GNU} M4 version 1.4.8 or later, though this is not
700 @xref{Autoconf 1}, for information about upgrading from version 1.
701 @xref{History}, for the story of Autoconf's development. @xref{FAQ},
702 for answers to some common questions about Autoconf.
704 See the @uref{http://www.gnu.org/software/autoconf/,
705 Autoconf web page} for up-to-date information, details on the mailing
706 lists, pointers to a list of known bugs, etc.
708 Mail suggestions to @email{autoconf@@gnu.org, the Autoconf mailing
709 list}. Past suggestions are
710 @uref{http://lists.gnu.org/archive/html/autoconf/, archived}.
712 Mail bug reports to @email{bug-autoconf@@gnu.org, the
713 Autoconf Bugs mailing list}. Past bug reports are
714 @uref{http://lists.gnu.org/archive/html/bug-autoconf/, archived}.
716 If possible, first check that your bug is
717 not already solved in current development versions, and that it has not
718 been reported yet. Be sure to include all the needed information and a
719 short @file{configure.ac} that demonstrates the problem.
721 Autoconf's development tree is accessible via anonymous @acronym{CVS}; see the
722 @uref{http://savannah.gnu.org/projects/autoconf/, Autoconf
723 Summary} for details. Patches relative to the
724 current @acronym{CVS} version can be sent for review to the
725 @email{autoconf-patches@@gnu.org, Autoconf Patches mailing list}.
727 @uref{http://lists.gnu.org/@/archive/@/html/@/autoconf-patches/, archived}.
729 Because of its mission, the Autoconf package itself
730 includes only a set of often-used
731 macros that have already demonstrated their usefulness. Nevertheless,
732 if you wish to share your macros, or find existing ones, see the
733 @uref{http://autoconf-archive.cryp.to/, Autoconf Macro
734 Archive}, which is kindly run by @email{simons@@cryp.to,
738 @c ================================================= The GNU Build System
740 @node The GNU Build System
741 @chapter The @acronym{GNU} Build System
742 @cindex @acronym{GNU} build system
744 Autoconf solves an important problem---reliable discovery of
745 system-specific build and runtime information---but this is only one
746 piece of the puzzle for the development of portable software. To this
747 end, the @acronym{GNU} project has developed a suite of integrated
748 utilities to finish the job Autoconf started: the @acronym{GNU} build
749 system, whose most important components are Autoconf, Automake, and
750 Libtool. In this chapter, we introduce you to those tools, point you
751 to sources of more information, and try to convince you to use the
752 entire @acronym{GNU} build system for your software.
755 * Automake:: Escaping makefile hell
756 * Gnulib:: The @acronym{GNU} portability library
757 * Libtool:: Building libraries portably
758 * Pointers:: More info on the @acronym{GNU} build system
764 The ubiquity of @command{make} means that a makefile is almost the
765 only viable way to distribute automatic build rules for software, but
766 one quickly runs into its numerous limitations. Its lack of
767 support for automatic dependency tracking, recursive builds in
768 subdirectories, reliable timestamps (e.g., for network file systems), and
769 so on, mean that developers must painfully (and often incorrectly)
770 reinvent the wheel for each project. Portability is non-trivial, thanks
771 to the quirks of @command{make} on many systems. On top of all this is the
772 manual labor required to implement the many standard targets that users
773 have come to expect (@code{make install}, @code{make distclean},
774 @code{make uninstall}, etc.). Since you are, of course, using Autoconf,
775 you also have to insert repetitive code in your @code{Makefile.in} to
776 recognize @code{@@CC@@}, @code{@@CFLAGS@@}, and other substitutions
777 provided by @command{configure}. Into this mess steps @dfn{Automake}.
780 Automake allows you to specify your build needs in a @code{Makefile.am}
781 file with a vastly simpler and more powerful syntax than that of a plain
782 makefile, and then generates a portable @code{Makefile.in} for
783 use with Autoconf. For example, the @code{Makefile.am} to build and
784 install a simple ``Hello world'' program might look like:
788 hello_SOURCES = hello.c
792 The resulting @code{Makefile.in} (~400 lines) automatically supports all
793 the standard targets, the substitutions provided by Autoconf, automatic
794 dependency tracking, @code{VPATH} building, and so on. @command{make}
795 builds the @code{hello} program, and @code{make install} installs it
796 in @file{/usr/local/bin} (or whatever prefix was given to
797 @command{configure}, if not @file{/usr/local}).
799 The benefits of Automake increase for larger packages (especially ones
800 with subdirectories), but even for small programs the added convenience
801 and portability can be substantial. And that's not all@enddots{}
806 @acronym{GNU} software has a well-deserved reputation for running on
807 many different types of systems. While our primary goal is to write
808 software for the @acronym{GNU} system, many users and developers have
809 been introduced to us through the systems that they were already using.
812 Gnulib is a central location for common @acronym{GNU} code, intended to
813 be shared among free software packages. Its components are typically
814 shared at the source level, rather than being a library that gets built,
815 installed, and linked against. The idea is to copy files from Gnulib
816 into your own source tree. There is no distribution tarball; developers
817 should just grab source modules from the repository. The source files
818 are available online, under various licenses, mostly @acronym{GNU}
819 @acronym{GPL} or @acronym{GNU} @acronym{LGPL}.
821 Gnulib modules typically contain C source code along with Autoconf
822 macros used to configure the source code. For example, the Gnulib
823 @code{stdbool} module implements a @file{stdbool.h} header that nearly
824 conforms to C99, even on old-fashioned hosts that lack @file{stdbool.h}.
825 This module contains a source file for the replacement header, along
826 with an Autoconf macro that arranges to use the replacement header on
827 old-fashioned systems.
832 Often, one wants to build not only programs, but libraries, so that
833 other programs can benefit from the fruits of your labor. Ideally, one
834 would like to produce @emph{shared} (dynamically linked) libraries,
835 which can be used by multiple programs without duplication on disk or in
836 memory and can be updated independently of the linked programs.
837 Producing shared libraries portably, however, is the stuff of
838 nightmares---each system has its own incompatible tools, compiler flags,
839 and magic incantations. Fortunately, @acronym{GNU} provides a solution:
843 Libtool handles all the requirements of building shared libraries for
844 you, and at this time seems to be the @emph{only} way to do so with any
845 portability. It also handles many other headaches, such as: the
846 interaction of Make rules with the variable suffixes of
847 shared libraries, linking reliably with shared libraries before they are
848 installed by the superuser, and supplying a consistent versioning system
849 (so that different versions of a library can be installed or upgraded
850 without breaking binary compatibility). Although Libtool, like
851 Autoconf, can be used without Automake, it is most simply utilized in
852 conjunction with Automake---there, Libtool is used automatically
853 whenever shared libraries are needed, and you need not know its syntax.
858 Developers who are used to the simplicity of @command{make} for small
859 projects on a single system might be daunted at the prospect of
860 learning to use Automake and Autoconf. As your software is
861 distributed to more and more users, however, you otherwise
862 quickly find yourself putting lots of effort into reinventing the
863 services that the @acronym{GNU} build tools provide, and making the
864 same mistakes that they once made and overcame. (Besides, since
865 you're already learning Autoconf, Automake is a piece of cake.)
867 There are a number of places that you can go to for more information on
868 the @acronym{GNU} build tools.
875 @uref{http://www.gnu.org/@/software/@/autoconf/, Autoconf},
876 @uref{http://www.gnu.org/@/software/@/automake/, Automake},
877 @uref{http://www.gnu.org/@/software/@/gnulib/, Gnulib}, and
878 @uref{http://www.gnu.org/@/software/@/libtool/, Libtool}.
880 @item Automake Manual
882 @xref{Top, , Automake, automake, @acronym{GNU} Automake}, for more
883 information on Automake.
887 The book @cite{@acronym{GNU} Autoconf, Automake and
888 Libtool}@footnote{@cite{@acronym{GNU} Autoconf, Automake and Libtool},
889 by G. V. Vaughan, B. Elliston, T. Tromey, and I. L. Taylor. SAMS (originally
890 New Riders), 2000, ISBN 1578701902.} describes the complete @acronym{GNU}
891 build environment. You can also find
892 @uref{http://sources.redhat.com/@/autobook/, the entire book on-line}.
896 @c ================================================= Making configure Scripts.
898 @node Making configure Scripts
899 @chapter Making @command{configure} Scripts
900 @cindex @file{aclocal.m4}
901 @cindex @command{configure}
903 The configuration scripts that Autoconf produces are by convention
904 called @command{configure}. When run, @command{configure} creates several
905 files, replacing configuration parameters in them with appropriate
906 values. The files that @command{configure} creates are:
910 one or more @file{Makefile} files, usually one in each subdirectory of the
911 package (@pxref{Makefile Substitutions});
914 optionally, a C header file, the name of which is configurable,
915 containing @code{#define} directives (@pxref{Configuration Headers});
918 a shell script called @file{config.status} that, when run, recreates
919 the files listed above (@pxref{config.status Invocation});
922 an optional shell script normally called @file{config.cache}
923 (created when using @samp{configure --config-cache}) that
924 saves the results of running many of the tests (@pxref{Cache Files});
927 a file called @file{config.log} containing any messages produced by
928 compilers, to help debugging if @command{configure} makes a mistake.
931 @cindex @file{configure.in}
932 @cindex @file{configure.ac}
933 To create a @command{configure} script with Autoconf, you need to write an
934 Autoconf input file @file{configure.ac} (or @file{configure.in}) and run
935 @command{autoconf} on it. If you write your own feature tests to
936 supplement those that come with Autoconf, you might also write files
937 called @file{aclocal.m4} and @file{acsite.m4}. If you use a C header
938 file to contain @code{#define} directives, you might also run
939 @command{autoheader}, and you can distribute the generated file
940 @file{config.h.in} with the package.
942 Here is a diagram showing how the files that can be used in
943 configuration are produced. Programs that are executed are suffixed by
944 @samp{*}. Optional files are enclosed in square brackets (@samp{[]}).
945 @command{autoconf} and @command{autoheader} also read the installed Autoconf
946 macro files (by reading @file{autoconf.m4}).
949 Files used in preparing a software package for distribution:
951 your source files --> [autoscan*] --> [configure.scan] --> configure.ac
955 | .------> autoconf* -----> configure
957 | `-----> [autoheader*] --> [config.h.in]
961 Makefile.in -------------------------------> Makefile.in
965 Files used in configuring a software package:
968 .-------------> [config.cache]
969 configure* ------------+-------------> config.log
971 [config.h.in] -. v .-> [config.h] -.
972 +--> config.status* -+ +--> make*
973 Makefile.in ---' `-> Makefile ---'
978 * Writing Autoconf Input:: What to put in an Autoconf input file
979 * autoscan Invocation:: Semi-automatic @file{configure.ac} writing
980 * ifnames Invocation:: Listing the conditionals in source code
981 * autoconf Invocation:: How to create configuration scripts
982 * autoreconf Invocation:: Remaking multiple @command{configure} scripts
985 @node Writing Autoconf Input
986 @section Writing @file{configure.ac}
988 To produce a @command{configure} script for a software package, create a
989 file called @file{configure.ac} that contains invocations of the
990 Autoconf macros that test the system features your package needs or can
991 use. Autoconf macros already exist to check for many features; see
992 @ref{Existing Tests}, for their descriptions. For most other features,
993 you can use Autoconf template macros to produce custom checks; see
994 @ref{Writing Tests}, for information about them. For especially tricky
995 or specialized features, @file{configure.ac} might need to contain some
996 hand-crafted shell commands; see @ref{Portable Shell}. The
997 @command{autoscan} program can give you a good start in writing
998 @file{configure.ac} (@pxref{autoscan Invocation}, for more information).
1000 Previous versions of Autoconf promoted the name @file{configure.in},
1001 which is somewhat ambiguous (the tool needed to process this file is not
1002 described by its extension), and introduces a slight confusion with
1003 @file{config.h.in} and so on (for which @samp{.in} means ``to be
1004 processed by @command{configure}''). Using @file{configure.ac} is now
1008 * Shell Script Compiler:: Autoconf as solution of a problem
1009 * Autoconf Language:: Programming in Autoconf
1010 * Autoconf Input Layout:: Standard organization of @file{configure.ac}
1013 @node Shell Script Compiler
1014 @subsection A Shell Script Compiler
1016 Just as for any other computer language, in order to properly program
1017 @file{configure.ac} in Autoconf you must understand @emph{what} problem
1018 the language tries to address and @emph{how} it does so.
1020 The problem Autoconf addresses is that the world is a mess. After all,
1021 you are using Autoconf in order to have your package compile easily on
1022 all sorts of different systems, some of them being extremely hostile.
1023 Autoconf itself bears the price for these differences: @command{configure}
1024 must run on all those systems, and thus @command{configure} must limit itself
1025 to their lowest common denominator of features.
1027 Naturally, you might then think of shell scripts; who needs
1028 @command{autoconf}? A set of properly written shell functions is enough to
1029 make it easy to write @command{configure} scripts by hand. Sigh!
1030 Unfortunately, shell functions do not belong to the least common
1031 denominator; therefore, where you would like to define a function and
1032 use it ten times, you would instead need to copy its body ten times.
1034 So, what is really needed is some kind of compiler, @command{autoconf},
1035 that takes an Autoconf program, @file{configure.ac}, and transforms it
1036 into a portable shell script, @command{configure}.
1038 How does @command{autoconf} perform this task?
1040 There are two obvious possibilities: creating a brand new language or
1041 extending an existing one. The former option is attractive: all
1042 sorts of optimizations could easily be implemented in the compiler and
1043 many rigorous checks could be performed on the Autoconf program
1044 (e.g., rejecting any non-portable construct). Alternatively, you can
1045 extend an existing language, such as the @code{sh} (Bourne shell)
1048 Autoconf does the latter: it is a layer on top of @code{sh}. It was
1049 therefore most convenient to implement @command{autoconf} as a macro
1050 expander: a program that repeatedly performs @dfn{macro expansions} on
1051 text input, replacing macro calls with macro bodies and producing a pure
1052 @code{sh} script in the end. Instead of implementing a dedicated
1053 Autoconf macro expander, it is natural to use an existing
1054 general-purpose macro language, such as M4, and implement the extensions
1055 as a set of M4 macros.
1058 @node Autoconf Language
1059 @subsection The Autoconf Language
1062 The Autoconf language differs from many other computer
1063 languages because it treats actual code the same as plain text. Whereas
1064 in C, for instance, data and instructions have different syntactic
1065 status, in Autoconf their status is rigorously the same. Therefore, we
1066 need a means to distinguish literal strings from text to be expanded:
1069 When calling macros that take arguments, there must not be any white
1070 space between the macro name and the open parenthesis. Arguments should
1071 be enclosed within the M4 quote characters @samp{[} and @samp{]}, and be
1072 separated by commas. Any leading blanks or newlines in arguments are ignored,
1073 unless they are quoted. You should always quote an argument that
1074 might contain a macro name, comma, parenthesis, or a leading blank or
1075 newline. This rule applies recursively for every macro
1076 call, including macros called from other macros.
1081 AC_CHECK_HEADER([stdio.h],
1082 [AC_DEFINE([HAVE_STDIO_H], [1],
1083 [Define to 1 if you have <stdio.h>.])],
1084 [AC_MSG_ERROR([Sorry, can't do anything for you])])
1088 is quoted properly. You may safely simplify its quotation to:
1091 AC_CHECK_HEADER([stdio.h],
1092 [AC_DEFINE([HAVE_STDIO_H], 1,
1093 [Define to 1 if you have <stdio.h>.])],
1094 [AC_MSG_ERROR([Sorry, can't do anything for you])])
1098 because @samp{1} cannot contain a macro call. Here, the argument of
1099 @code{AC_MSG_ERROR} must be quoted; otherwise, its comma would be
1100 interpreted as an argument separator. Also, the second and third arguments
1101 of @samp{AC_CHECK_HEADER} must be quoted, since they contain
1102 macro calls. The three arguments @samp{HAVE_STDIO_H}, @samp{stdio.h},
1103 and @samp{Define to 1 if you have <stdio.h>.} do not need quoting, but
1104 if you unwisely defined a macro with a name like @samp{Define} or
1105 @samp{stdio} then they would need quoting. Cautious Autoconf users
1106 would keep the quotes, but many Autoconf users find such precautions
1107 annoying, and would rewrite the example as follows:
1110 AC_CHECK_HEADER(stdio.h,
1111 [AC_DEFINE(HAVE_STDIO_H, 1,
1112 [Define to 1 if you have <stdio.h>.])],
1113 [AC_MSG_ERROR([Sorry, can't do anything for you])])
1117 This is safe, so long as you adopt good naming conventions and do not
1118 define macros with names like @samp{HAVE_STDIO_H}, @samp{stdio}, or
1119 @samp{h}. Though it is also safe here to omit the quotes around
1120 @samp{Define to 1 if you have <stdio.h>.} this is not recommended, as
1121 message strings are more likely to inadvertently contain commas.
1123 The following example is wrong and dangerous, as it is underquoted:
1126 AC_CHECK_HEADER(stdio.h,
1127 AC_DEFINE(HAVE_STDIO_H, 1,
1128 Define to 1 if you have <stdio.h>.),
1129 AC_MSG_ERROR([Sorry, can't do anything for you]))
1132 In other cases, you may have to use text that also resembles a macro
1133 call. You must quote that text even when it is not passed as a macro
1137 echo "Hard rock was here! --[AC_DC]"
1144 echo "Hard rock was here! --AC_DC"
1148 When you use the same text in a macro argument, you must therefore have
1149 an extra quotation level (since one is stripped away by the macro
1150 substitution). In general, then, it is a good idea to @emph{use double
1151 quoting for all literal string arguments}:
1154 AC_MSG_WARN([[AC_DC stinks --Iron Maiden]])
1157 You are now able to understand one of the constructs of Autoconf that
1158 has been continually misunderstood@dots{} The rule of thumb is that
1159 @emph{whenever you expect macro expansion, expect quote expansion};
1160 i.e., expect one level of quotes to be lost. For instance:
1163 AC_COMPILE_IFELSE([char b[10];], [], [AC_MSG_ERROR([you lose])])
1167 is incorrect: here, the first argument of @code{AC_COMPILE_IFELSE} is
1168 @samp{char b[10];} and is expanded once, which results in
1169 @samp{char b10;}. (There was an idiom common in Autoconf's past to
1170 address this issue via the M4 @code{changequote} primitive, but do not
1171 use it!) Let's take a closer look: the author meant the first argument
1172 to be understood as a literal, and therefore it must be quoted twice:
1175 AC_COMPILE_IFELSE([[char b[10];]], [], [AC_MSG_ERROR([you lose])])
1179 Voil@`a, you actually produce @samp{char b[10];} this time!
1181 On the other hand, descriptions (e.g., the last parameter of
1182 @code{AC_DEFINE} or @code{AS_HELP_STRING}) are not literals---they
1183 are subject to line breaking, for example---and should not be double quoted.
1184 Even if these descriptions are short and are not actually broken, double
1185 quoting them yields weird results.
1187 Some macros take optional arguments, which this documentation represents
1188 as @ovar{arg} (not to be confused with the quote characters). You may
1189 just leave them empty, or use @samp{[]} to make the emptiness of the
1190 argument explicit, or you may simply omit the trailing commas. The
1191 three lines below are equivalent:
1194 AC_CHECK_HEADERS([stdio.h], [], [], [])
1195 AC_CHECK_HEADERS([stdio.h],,,)
1196 AC_CHECK_HEADERS([stdio.h])
1199 It is best to put each macro call on its own line in
1200 @file{configure.ac}. Most of the macros don't add extra newlines; they
1201 rely on the newline after the macro call to terminate the commands.
1202 This approach makes the generated @command{configure} script a little
1203 easier to read by not inserting lots of blank lines. It is generally
1204 safe to set shell variables on the same line as a macro call, because
1205 the shell allows assignments without intervening newlines.
1207 You can include comments in @file{configure.ac} files by starting them
1208 with the @samp{#}. For example, it is helpful to begin
1209 @file{configure.ac} files with a line like this:
1212 # Process this file with autoconf to produce a configure script.
1215 @node Autoconf Input Layout
1216 @subsection Standard @file{configure.ac} Layout
1218 The order in which @file{configure.ac} calls the Autoconf macros is not
1219 important, with a few exceptions. Every @file{configure.ac} must
1220 contain a call to @code{AC_INIT} before the checks, and a call to
1221 @code{AC_OUTPUT} at the end (@pxref{Output}). Additionally, some macros
1222 rely on other macros having been called first, because they check
1223 previously set values of some variables to decide what to do. These
1224 macros are noted in the individual descriptions (@pxref{Existing
1225 Tests}), and they also warn you when @command{configure} is created if they
1226 are called out of order.
1228 To encourage consistency, here is a suggested order for calling the
1229 Autoconf macros. Generally speaking, the things near the end of this
1230 list are those that could depend on things earlier in it. For example,
1231 library functions could be affected by types and libraries.
1235 Autoconf requirements
1236 @code{AC_INIT(@var{package}, @var{version}, @var{bug-report-address})}
1237 information on the package
1239 checks for libraries
1240 checks for header files
1242 checks for structures
1243 checks for compiler characteristics
1244 checks for library functions
1245 checks for system services
1246 @code{AC_CONFIG_FILES(@r{[}@var{file@dots{}}@r{]})}
1252 @node autoscan Invocation
1253 @section Using @command{autoscan} to Create @file{configure.ac}
1254 @cindex @command{autoscan}
1256 The @command{autoscan} program can help you create and/or maintain a
1257 @file{configure.ac} file for a software package. @command{autoscan}
1258 examines source files in the directory tree rooted at a directory given
1259 as a command line argument, or the current directory if none is given.
1260 It searches the source files for common portability problems and creates
1261 a file @file{configure.scan} which is a preliminary @file{configure.ac}
1262 for that package, and checks a possibly existing @file{configure.ac} for
1265 When using @command{autoscan} to create a @file{configure.ac}, you
1266 should manually examine @file{configure.scan} before renaming it to
1267 @file{configure.ac}; it probably needs some adjustments.
1268 Occasionally, @command{autoscan} outputs a macro in the wrong order
1269 relative to another macro, so that @command{autoconf} produces a warning;
1270 you need to move such macros manually. Also, if you want the package to
1271 use a configuration header file, you must add a call to
1272 @code{AC_CONFIG_HEADERS} (@pxref{Configuration Headers}). You might
1273 also have to change or add some @code{#if} directives to your program in
1274 order to make it work with Autoconf (@pxref{ifnames Invocation}, for
1275 information about a program that can help with that job).
1277 When using @command{autoscan} to maintain a @file{configure.ac}, simply
1278 consider adding its suggestions. The file @file{autoscan.log}
1279 contains detailed information on why a macro is requested.
1281 @command{autoscan} uses several data files (installed along with Autoconf)
1282 to determine which macros to output when it finds particular symbols in
1283 a package's source files. These data files all have the same format:
1284 each line consists of a symbol, one or more blanks, and the Autoconf macro to
1285 output if that symbol is encountered. Lines starting with @samp{#} are
1288 @command{autoscan} accepts the following options:
1293 Print a summary of the command line options and exit.
1297 Print the version number of Autoconf and exit.
1301 Print the names of the files it examines and the potentially interesting
1302 symbols it finds in them. This output can be voluminous.
1304 @item --include=@var{dir}
1306 Append @var{dir} to the include path. Multiple invocations accumulate.
1308 @item --prepend-include=@var{dir}
1310 Prepend @var{dir} to the include path. Multiple invocations accumulate.
1313 @node ifnames Invocation
1314 @section Using @command{ifnames} to List Conditionals
1315 @cindex @command{ifnames}
1317 @command{ifnames} can help you write @file{configure.ac} for a software
1318 package. It prints the identifiers that the package already uses in C
1319 preprocessor conditionals. If a package has already been set up to have
1320 some portability, @command{ifnames} can thus help you figure out what its
1321 @command{configure} needs to check for. It may help fill in some gaps in a
1322 @file{configure.ac} generated by @command{autoscan} (@pxref{autoscan
1325 @command{ifnames} scans all of the C source files named on the command line
1326 (or the standard input, if none are given) and writes to the standard
1327 output a sorted list of all the identifiers that appear in those files
1328 in @code{#if}, @code{#elif}, @code{#ifdef}, or @code{#ifndef}
1329 directives. It prints each identifier on a line, followed by a
1330 space-separated list of the files in which that identifier occurs.
1333 @command{ifnames} accepts the following options:
1338 Print a summary of the command line options and exit.
1342 Print the version number of Autoconf and exit.
1345 @node autoconf Invocation
1346 @section Using @command{autoconf} to Create @command{configure}
1347 @cindex @command{autoconf}
1349 To create @command{configure} from @file{configure.ac}, run the
1350 @command{autoconf} program with no arguments. @command{autoconf} processes
1351 @file{configure.ac} with the M4 macro processor, using the
1352 Autoconf macros. If you give @command{autoconf} an argument, it reads that
1353 file instead of @file{configure.ac} and writes the configuration script
1354 to the standard output instead of to @command{configure}. If you give
1355 @command{autoconf} the argument @option{-}, it reads from the standard
1356 input instead of @file{configure.ac} and writes the configuration script
1357 to the standard output.
1359 The Autoconf macros are defined in several files. Some of the files are
1360 distributed with Autoconf; @command{autoconf} reads them first. Then it
1361 looks for the optional file @file{acsite.m4} in the directory that
1362 contains the distributed Autoconf macro files, and for the optional file
1363 @file{aclocal.m4} in the current directory. Those files can contain
1364 your site's or the package's own Autoconf macro definitions
1365 (@pxref{Writing Autoconf Macros}, for more information). If a macro is
1366 defined in more than one of the files that @command{autoconf} reads, the
1367 last definition it reads overrides the earlier ones.
1369 @command{autoconf} accepts the following options:
1374 Print a summary of the command line options and exit.
1378 Print the version number of Autoconf and exit.
1382 Report processing steps.
1386 Don't remove the temporary files.
1390 Remake @file{configure} even if newer than its input files.
1392 @item --include=@var{dir}
1394 Append @var{dir} to the include path. Multiple invocations accumulate.
1396 @item --prepend-include=@var{dir}
1398 Prepend @var{dir} to the include path. Multiple invocations accumulate.
1400 @item --output=@var{file}
1401 @itemx -o @var{file}
1402 Save output (script or trace) to @var{file}. The file @option{-} stands
1403 for the standard output.
1405 @item --warnings=@var{category}
1406 @itemx -W @var{category}
1408 Report the warnings related to @var{category} (which can actually be a
1409 comma separated list). @xref{Reporting Messages}, macro
1410 @code{AC_DIAGNOSE}, for a comprehensive list of categories. Special
1415 report all the warnings
1421 treats warnings as errors
1423 @item no-@var{category}
1424 disable warnings falling into @var{category}
1427 Warnings about @samp{syntax} are enabled by default, and the environment
1428 variable @env{WARNINGS}, a comma separated list of categories, is
1429 honored as well. Passing @option{-W @var{category}} actually behaves as if
1430 you had passed @option{--warnings=syntax,$WARNINGS,@var{category}}. If
1431 you want to disable the defaults and @env{WARNINGS}, but (for example)
1432 enable the warnings about obsolete constructs, you would use @option{-W
1436 @cindex Macro invocation stack
1437 Because @command{autoconf} uses @command{autom4te} behind the scenes, it
1438 displays a back trace for errors, but not for warnings; if you want
1439 them, just pass @option{-W error}. @xref{autom4te Invocation}, for some
1442 @item --trace=@var{macro}[:@var{format}]
1443 @itemx -t @var{macro}[:@var{format}]
1444 Do not create the @command{configure} script, but list the calls to
1445 @var{macro} according to the @var{format}. Multiple @option{--trace}
1446 arguments can be used to list several macros. Multiple @option{--trace}
1447 arguments for a single macro are not cumulative; instead, you should
1448 just make @var{format} as long as needed.
1450 The @var{format} is a regular string, with newlines if desired, and
1451 several special escape codes. It defaults to @samp{$f:$l:$n:$%}; see
1452 @ref{autom4te Invocation}, for details on the @var{format}.
1454 @item --initialization
1456 By default, @option{--trace} does not trace the initialization of the
1457 Autoconf macros (typically the @code{AC_DEFUN} definitions). This
1458 results in a noticeable speedup, but can be disabled by this option.
1462 It is often necessary to check the content of a @file{configure.ac}
1463 file, but parsing it yourself is extremely fragile and error-prone. It
1464 is suggested that you rely upon @option{--trace} to scan
1465 @file{configure.ac}. For instance, to find the list of variables that
1466 are substituted, use:
1470 $ @kbd{autoconf -t AC_SUBST}
1471 configure.ac:2:AC_SUBST:ECHO_C
1472 configure.ac:2:AC_SUBST:ECHO_N
1473 configure.ac:2:AC_SUBST:ECHO_T
1474 @i{More traces deleted}
1479 The example below highlights the difference between @samp{$@@},
1480 @samp{$*}, and @samp{$%}.
1484 $ @kbd{cat configure.ac}
1485 AC_DEFINE(This, is, [an
1487 $ @kbd{autoconf -t 'AC_DEFINE:@@: $@@}
1494 %: This:is:an [example]
1499 The @var{format} gives you a lot of freedom:
1503 $ @kbd{autoconf -t 'AC_SUBST:$$ac_subst@{"$1"@} = "$f:$l";'}
1504 $ac_subst@{"ECHO_C"@} = "configure.ac:2";
1505 $ac_subst@{"ECHO_N"@} = "configure.ac:2";
1506 $ac_subst@{"ECHO_T"@} = "configure.ac:2";
1507 @i{More traces deleted}
1512 A long @var{separator} can be used to improve the readability of complex
1513 structures, and to ease their parsing (for instance when no single
1514 character is suitable as a separator):
1518 $ @kbd{autoconf -t 'AM_MISSING_PROG:$@{|:::::|@}*'}
1519 ACLOCAL|:::::|aclocal|:::::|$missing_dir
1520 AUTOCONF|:::::|autoconf|:::::|$missing_dir
1521 AUTOMAKE|:::::|automake|:::::|$missing_dir
1522 @i{More traces deleted}
1526 @node autoreconf Invocation
1527 @section Using @command{autoreconf} to Update @command{configure} Scripts
1528 @cindex @command{autoreconf}
1530 Installing the various components of the @acronym{GNU} Build System can be
1531 tedious: running @command{autopoint} for Gettext, @command{automake} for
1532 @file{Makefile.in} etc.@: in each directory. It may be needed either
1533 because some tools such as @command{automake} have been updated on your
1534 system, or because some of the sources such as @file{configure.ac} have
1535 been updated, or finally, simply in order to install the @acronym{GNU} Build
1536 System in a fresh tree.
1538 @command{autoreconf} runs @command{autoconf}, @command{autoheader},
1539 @command{aclocal}, @command{automake}, @command{libtoolize}, and
1540 @command{autopoint} (when appropriate) repeatedly to update the
1541 @acronym{GNU} Build System in the specified directories and their
1542 subdirectories (@pxref{Subdirectories}). By default, it only remakes
1543 those files that are older than their sources.
1545 If you install a new version of some tool, you can make
1546 @command{autoreconf} remake @emph{all} of the files by giving it the
1547 @option{--force} option.
1549 @xref{Automatic Remaking}, for Make rules to automatically
1550 remake @command{configure} scripts when their source files change. That
1551 method handles the timestamps of configuration header templates
1552 properly, but does not pass @option{--autoconf-dir=@var{dir}} or
1553 @option{--localdir=@var{dir}}.
1556 @cindex @command{autopoint}
1557 Gettext supplies the @command{autopoint} command to add translation
1558 infrastructure to a source package. If you use @command{autopoint},
1559 your @file{configure.ac} should invoke both @code{AM_GNU_GETTEXT} and
1560 @code{AM_GNU_GETTEXT_VERSION(@var{gettext-version})}. @xref{autopoint
1561 Invocation, , Invoking the @code{autopoint} Program, gettext,
1562 @acronym{GNU} @code{gettext} utilities}, for further details.
1565 @command{autoreconf} accepts the following options:
1570 Print a summary of the command line options and exit.
1574 Print the version number of Autoconf and exit.
1577 Print the name of each directory @command{autoreconf} examines and the
1578 commands it runs. If given two or more times, pass @option{--verbose}
1579 to subordinate tools that support it.
1583 Don't remove the temporary files.
1587 Remake even @file{configure} scripts and configuration headers that are
1588 newer than their input files (@file{configure.ac} and, if present,
1593 Install the missing auxiliary files in the package. By default, files
1594 are copied; this can be changed with @option{--symlink}.
1596 If deemed appropriate, this option triggers calls to
1597 @samp{automake --add-missing},
1598 @samp{libtoolize}, @samp{autopoint}, etc.
1600 @item --no-recursive
1601 Do not rebuild files in subdirectories to configure (see @ref{Subdirectories},
1602 macro @code{AC_CONFIG_SUBDIRS}).
1606 When used with @option{--install}, install symbolic links to the missing
1607 auxiliary files instead of copying them.
1611 When the directories were configured, update the configuration by
1612 running @samp{./config.status --recheck && ./config.status}, and then
1615 @item --include=@var{dir}
1617 Append @var{dir} to the include path. Multiple invocations accumulate.
1618 Passed on to @command{autoconf} and @command{autoheader} internally.
1620 @item --prepend-include=@var{dir}
1622 Prepend @var{dir} to the include path. Multiple invocations accumulate.
1623 Passed on to @command{autoconf} and @command{autoheader} internally.
1625 @item --warnings=@var{category}
1626 @itemx -W @var{category}
1628 Report the warnings related to @var{category} (which can actually be a
1629 comma separated list).
1633 related to cross compilation issues.
1636 report the uses of obsolete constructs.
1642 dubious syntactic constructs.
1645 report all the warnings
1651 treats warnings as errors
1653 @item no-@var{category}
1654 disable warnings falling into @var{category}
1657 Warnings about @samp{syntax} are enabled by default, and the environment
1658 variable @env{WARNINGS}, a comma separated list of categories, is
1659 honored as well. Passing @option{-W @var{category}} actually behaves as if
1660 you had passed @option{--warnings=syntax,$WARNINGS,@var{category}}. If
1661 you want to disable the defaults and @env{WARNINGS}, but (for example)
1662 enable the warnings about obsolete constructs, you would use @option{-W
1666 If you want @command{autoreconf} to pass flags that are not listed here
1667 on to @command{aclocal}, set @code{ACLOCAL_AMFLAGS} in your @file{Makefile.am}.
1669 @c ========================================= Initialization and Output Files.
1672 @chapter Initialization and Output Files
1674 Autoconf-generated @command{configure} scripts need some information about
1675 how to initialize, such as how to find the package's source files and
1676 about the output files to produce. The following sections describe the
1677 initialization and the creation of output files.
1680 * Initializing configure:: Option processing etc.
1681 * Notices:: Copyright, version numbers in @command{configure}
1682 * Input:: Where Autoconf should find files
1683 * Output:: Outputting results from the configuration
1684 * Configuration Actions:: Preparing the output based on results
1685 * Configuration Files:: Creating output files
1686 * Makefile Substitutions:: Using output variables in makefiles
1687 * Configuration Headers:: Creating a configuration header file
1688 * Configuration Commands:: Running arbitrary instantiation commands
1689 * Configuration Links:: Links depending on the configuration
1690 * Subdirectories:: Configuring independent packages together
1691 * Default Prefix:: Changing the default installation prefix
1694 @node Initializing configure
1695 @section Initializing @command{configure}
1697 Every @command{configure} script must call @code{AC_INIT} before doing
1698 anything else. The only other required macro is @code{AC_OUTPUT}
1701 @defmac AC_INIT (@var{package}, @var{version}, @ovar{bug-report}, @ovar{tarname})
1703 Process any command-line arguments and perform various initializations
1706 Set the name of the @var{package} and its @var{version}. These are
1707 typically used in @option{--version} support, including that of
1708 @command{configure}. The optional argument @var{bug-report} should be
1709 the email to which users should send bug reports. The package
1710 @var{tarname} differs from @var{package}: the latter designates the full
1711 package name (e.g., @samp{GNU Autoconf}), while the former is meant for
1712 distribution tar ball names (e.g., @samp{autoconf}). It defaults to
1713 @var{package} with @samp{GNU } stripped, lower-cased, and all characters
1714 other than alphanumerics and underscores are changed to @samp{-}.
1716 It is preferable that the arguments of @code{AC_INIT} be static, i.e.,
1717 there should not be any shell computation, but they can be computed by
1720 The following M4 macros (e.g., @code{AC_PACKAGE_NAME}), output variables
1721 (e.g., @code{PACKAGE_NAME}), and preprocessor symbols (e.g.,
1722 @code{PACKAGE_NAME}) are defined by @code{AC_INIT}:
1725 @item @code{AC_PACKAGE_NAME}, @code{PACKAGE_NAME}
1726 @acindex{PACKAGE_NAME}
1727 @ovindex PACKAGE_NAME
1728 @cvindex PACKAGE_NAME
1729 Exactly @var{package}.
1731 @item @code{AC_PACKAGE_TARNAME}, @code{PACKAGE_TARNAME}
1732 @acindex{PACKAGE_TARNAME}
1733 @ovindex PACKAGE_TARNAME
1734 @cvindex PACKAGE_TARNAME
1735 Exactly @var{tarname}.
1737 @item @code{AC_PACKAGE_VERSION}, @code{PACKAGE_VERSION}
1738 @acindex{PACKAGE_VERSION}
1739 @ovindex PACKAGE_VERSION
1740 @cvindex PACKAGE_VERSION
1741 Exactly @var{version}.
1743 @item @code{AC_PACKAGE_STRING}, @code{PACKAGE_STRING}
1744 @acindex{PACKAGE_STRING}
1745 @ovindex PACKAGE_STRING
1746 @cvindex PACKAGE_STRING
1747 Exactly @samp{@var{package} @var{version}}.
1749 @item @code{AC_PACKAGE_BUGREPORT}, @code{PACKAGE_BUGREPORT}
1750 @acindex{PACKAGE_BUGREPORT}
1751 @ovindex PACKAGE_BUGREPORT
1752 @cvindex PACKAGE_BUGREPORT
1753 Exactly @var{bug-report}.
1757 If your @command{configure} script does its own option processing, it
1758 should inspect @samp{$@@} or @samp{$*} immediately after calling
1759 @code{AC_INIT}, because other Autoconf macros liberally use the
1760 @command{set} command to process strings, and this has the side effect
1761 of updating @samp{$@@} and @samp{$*}. However, we suggest that you use
1762 standard macros like @code{AC_ARG_ENABLE} instead of attempting to
1763 implement your own option processing. @xref{Site Configuration}.
1767 @section Notices in @command{configure}
1768 @cindex Notices in @command{configure}
1770 The following macros manage version numbers for @command{configure}
1771 scripts. Using them is optional.
1773 @c FIXME: AC_PREREQ should not be here
1774 @defmac AC_PREREQ (@var{version})
1777 Ensure that a recent enough version of Autoconf is being used. If the
1778 version of Autoconf being used to create @command{configure} is
1779 earlier than @var{version}, print an error message to the standard
1780 error output and exit with failure (exit status is 63). For example:
1783 AC_PREREQ([@value{VERSION}])
1786 This macro is the only macro that may be used before @code{AC_INIT}, but
1787 for consistency, you are invited not to do so.
1790 @defmac AC_COPYRIGHT (@var{copyright-notice})
1792 @cindex Copyright Notice
1793 State that, in addition to the Free Software Foundation's copyright on
1794 the Autoconf macros, parts of your @command{configure} are covered by the
1795 @var{copyright-notice}.
1797 The @var{copyright-notice} shows up in both the head of
1798 @command{configure} and in @samp{configure --version}.
1802 @defmac AC_REVISION (@var{revision-info})
1805 Copy revision stamp @var{revision-info} into the @command{configure}
1806 script, with any dollar signs or double-quotes removed. This macro lets
1807 you put a revision stamp from @file{configure.ac} into @command{configure}
1808 without @acronym{RCS} or @acronym{CVS} changing it when you check in
1809 @command{configure}. That way, you can determine easily which revision of
1810 @file{configure.ac} a particular @command{configure} corresponds to.
1812 For example, this line in @file{configure.ac}:
1814 @c The asis prevents RCS from changing the example in the manual.
1816 AC_REVISION([$@asis{Revision: 1.30 }$])
1820 produces this in @command{configure}:
1824 # From configure.ac Revision: 1.30
1830 @section Finding @command{configure} Input
1833 @defmac AC_CONFIG_SRCDIR (@var{unique-file-in-source-dir})
1834 @acindex{CONFIG_SRCDIR}
1835 @var{unique-file-in-source-dir} is some file that is in the package's
1836 source directory; @command{configure} checks for this file's existence to
1837 make sure that the directory that it is told contains the source code in
1838 fact does. Occasionally people accidentally specify the wrong directory
1839 with @option{--srcdir}; this is a safety check. @xref{configure
1840 Invocation}, for more information.
1844 @c FIXME: Remove definitively once --install explained.
1846 @c Small packages may store all their macros in @code{aclocal.m4}. As the
1847 @c set of macros grows, or for maintenance reasons, a maintainer may prefer
1848 @c to split the macros in several files. In this case, Autoconf must be
1849 @c told which files to load, and in which order.
1851 @c @defmac AC_INCLUDE (@var{file}@dots{})
1852 @c @acindex{INCLUDE}
1853 @c @c FIXME: There is no longer shell globbing.
1854 @c Read the macro definitions that appear in the listed files. A list of
1855 @c space-separated file names or shell globbing patterns is expected. The
1856 @c files are read in the order they're listed.
1858 @c Because the order of definition of macros is important (only the last
1859 @c definition of a macro is used), beware that it is @code{AC_INIT} that
1860 @c loads @file{acsite.m4} and @file{aclocal.m4}. Note that
1861 @c @code{AC_INCLUDE}ing a file before @code{AC_INIT} or within
1862 @c @file{aclocal.m4} is different from doing so after @code{AC_INIT}: in
1863 @c the latter case, non-macro lines from included files may end up in the
1864 @c @file{configure} script, whereas in the former case, they'd be discarded
1865 @c just like any text that appear before @code{AC_INIT}.
1868 Packages that do manual configuration or use the @command{install} program
1869 might need to tell @command{configure} where to find some other shell
1870 scripts by calling @code{AC_CONFIG_AUX_DIR}, though the default places
1871 it looks are correct for most cases.
1873 @defmac AC_CONFIG_AUX_DIR (@var{dir})
1874 @acindex{CONFIG_AUX_DIR}
1875 Use the auxiliary build tools (e.g., @file{install-sh},
1876 @file{config.sub}, @file{config.guess}, Cygnus @command{configure},
1877 Automake and Libtool scripts, etc.)@: that are in directory @var{dir}.
1878 These are auxiliary files used in configuration. @var{dir} can be
1879 either absolute or relative to @file{@var{srcdir}}. The default is
1880 @file{@var{srcdir}} or @file{@var{srcdir}/..} or
1881 @file{@var{srcdir}/../..}, whichever is the first that contains
1882 @file{install-sh}. The other files are not checked for, so that using
1883 @code{AC_PROG_INSTALL} does not automatically require distributing the
1884 other auxiliary files. It checks for @file{install.sh} also, but that
1885 name is obsolete because some @code{make} have a rule that creates
1886 @file{install} from it if there is no makefile.
1888 The auxiliary directory is commonly named @file{build-aux}.
1889 If you need portability to @acronym{DOS} variants, do not name the
1890 auxiliary directory @file{aux}. @xref{File System Conventions}.
1893 @defmac AC_REQUIRE_AUX_FILE (@var{file})
1894 @acindex{REQUIRE_AUX_FILE}
1895 Declares that @var{file} is expected in the directory defined above. In
1896 Autoconf proper, this macro does nothing: its sole purpose is to be
1897 traced by third-party tools to produce a list of expected auxiliary
1898 files. For instance it is called by macros like @code{AC_PROG_INSTALL}
1899 (@pxref{Particular Programs}) or @code{AC_CANONICAL_BUILD}
1900 (@pxref{Canonicalizing}) to register the auxiliary files they need.
1903 Similarly, packages that use @command{aclocal} should declare where
1904 local macros can be found using @code{AC_CONFIG_MACRO_DIR}.
1906 @defmac AC_CONFIG_MACRO_DIR (@var{dir})
1907 @acindex{CONFIG_MACRO_DIR}
1908 Specify @var{dir} as the location of additional local Autoconf macros.
1909 This macro is intended for use by future versions of commands like
1910 @command{autoreconf} that trace macro calls. It should be called
1911 directly from @file{configure.ac} so that tools that install macros for
1912 @command{aclocal} can find the macros' declarations.
1917 @section Outputting Files
1918 @cindex Outputting files
1920 Every Autoconf script, e.g., @file{configure.ac}, should finish by
1921 calling @code{AC_OUTPUT}. That is the macro that generates and runs
1922 @file{config.status}, which in turn creates the makefiles and any
1923 other files resulting from configuration. This is the only required
1924 macro besides @code{AC_INIT} (@pxref{Input}).
1928 @cindex Instantiation
1929 Generate @file{config.status} and launch it. Call this macro once, at
1930 the end of @file{configure.ac}.
1932 @file{config.status} performs all the configuration actions: all the
1933 output files (see @ref{Configuration Files}, macro
1934 @code{AC_CONFIG_FILES}), header files (see @ref{Configuration Headers},
1935 macro @code{AC_CONFIG_HEADERS}), commands (see @ref{Configuration
1936 Commands}, macro @code{AC_CONFIG_COMMANDS}), links (see
1937 @ref{Configuration Links}, macro @code{AC_CONFIG_LINKS}), subdirectories
1938 to configure (see @ref{Subdirectories}, macro @code{AC_CONFIG_SUBDIRS})
1941 The location of your @code{AC_OUTPUT} invocation is the exact point
1942 where configuration actions are taken: any code afterwards is
1943 executed by @code{configure} once @command{config.status} was run. If
1944 you want to bind actions to @command{config.status} itself
1945 (independently of whether @command{configure} is being run), see
1946 @ref{Configuration Commands, , Running Arbitrary Configuration
1950 Historically, the usage of @code{AC_OUTPUT} was somewhat different.
1951 @xref{Obsolete Macros}, for a description of the arguments that
1952 @code{AC_OUTPUT} used to support.
1955 If you run @command{make} in subdirectories, you should run it using the
1956 @code{make} variable @code{MAKE}. Most versions of @command{make} set
1957 @code{MAKE} to the name of the @command{make} program plus any options it
1958 was given. (But many do not include in it the values of any variables
1959 set on the command line, so those are not passed on automatically.)
1960 Some old versions of @command{make} do not set this variable. The
1961 following macro allows you to use it even with those versions.
1963 @defmac AC_PROG_MAKE_SET
1964 @acindex{PROG_MAKE_SET}
1966 If the Make command, @code{$MAKE} if set or else @samp{make}, predefines
1967 @code{$(MAKE)}, define output variable @code{SET_MAKE} to be empty.
1968 Otherwise, define @code{SET_MAKE} to a macro definition that sets
1969 @code{$(MAKE)}, such as @samp{MAKE=make}. Calls @code{AC_SUBST} for
1973 If you use this macro, place a line like this in each @file{Makefile.in}
1974 that runs @code{MAKE} on other directories:
1982 @node Configuration Actions
1983 @section Performing Configuration Actions
1984 @cindex Configuration actions
1986 @file{configure} is designed so that it appears to do everything itself,
1987 but there is actually a hidden slave: @file{config.status}.
1988 @file{configure} is in charge of examining your system, but it is
1989 @file{config.status} that actually takes the proper actions based on the
1990 results of @file{configure}. The most typical task of
1991 @file{config.status} is to @emph{instantiate} files.
1993 This section describes the common behavior of the four standard
1994 instantiating macros: @code{AC_CONFIG_FILES}, @code{AC_CONFIG_HEADERS},
1995 @code{AC_CONFIG_COMMANDS} and @code{AC_CONFIG_LINKS}. They all
1996 have this prototype:
1998 @c FIXME: Can't use @ovar here, Texinfo 4.0 goes lunatic and emits something
2001 AC_CONFIG_FOOS(@var{tag}@dots{}, [@var{commands}], [@var{init-cmds}])
2005 where the arguments are:
2009 A blank-or-newline-separated list of tags, which are typically the names of
2010 the files to instantiate.
2012 You are encouraged to use literals as @var{tags}. In particular, you
2016 @dots{} && my_foos="$my_foos fooo"
2017 @dots{} && my_foos="$my_foos foooo"
2018 AC_CONFIG_FOOS([$my_foos])
2022 and use this instead:
2025 @dots{} && AC_CONFIG_FOOS([fooo])
2026 @dots{} && AC_CONFIG_FOOS([foooo])
2029 The macros @code{AC_CONFIG_FILES} and @code{AC_CONFIG_HEADERS} use
2030 special @var{tag} values: they may have the form @samp{@var{output}} or
2031 @samp{@var{output}:@var{inputs}}. The file @var{output} is instantiated
2032 from its templates, @var{inputs} (defaulting to @samp{@var{output}.in}).
2034 @samp{AC_CONFIG_FILES([Makefile:boiler/top.mk:boiler/bot.mk)]},
2035 for example, asks for
2036 the creation of the file @file{Makefile} that contains the expansion of the
2037 output variables in the concatenation of @file{boiler/top.mk} and
2038 @file{boiler/bot.mk}.
2040 The special value @samp{-} might be used to denote the standard output
2041 when used in @var{output}, or the standard input when used in the
2042 @var{inputs}. You most probably don't need to use this in
2043 @file{configure.ac}, but it is convenient when using the command line
2044 interface of @file{./config.status}, see @ref{config.status Invocation},
2047 The @var{inputs} may be absolute or relative file names. In the latter
2048 case they are first looked for in the build tree, and then in the source
2052 Shell commands output literally into @file{config.status}, and
2053 associated with a tag that the user can use to tell @file{config.status}
2054 which the commands to run. The commands are run each time a @var{tag}
2055 request is given to @file{config.status}, typically each time the file
2056 @file{@var{tag}} is created.
2058 The variables set during the execution of @command{configure} are
2059 @emph{not} available here: you first need to set them via the
2060 @var{init-cmds}. Nonetheless the following variables are precomputed:
2064 The name of the top source directory, assuming that the working
2065 directory is the top build directory. This
2066 is what the @command{configure} option @option{--srcdir} sets.
2069 The name of the top source directory, assuming that the working
2070 directory is the current build directory.
2073 @item ac_top_build_prefix
2074 The name of the top build directory, assuming that the working
2075 directory is the current build directory.
2076 It can be empty, or else ends with a slash, so that you may concatenate
2080 The name of the corresponding source directory, assuming that the
2081 working directory is the current build directory.
2085 The @dfn{current} directory refers to the directory (or
2086 pseudo-directory) containing the input part of @var{tags}. For
2090 AC_CONFIG_COMMANDS([deep/dir/out:in/in.in], [@dots{}], [@dots{}])
2094 with @option{--srcdir=../package} produces the following values:
2097 # Argument of --srcdir
2099 # Reversing deep/dir
2100 ac_top_build_prefix='../../'
2101 # Concatenation of $ac_top_build_prefix and srcdir
2102 ac_top_srcdir='../../../package'
2103 # Concatenation of $ac_top_srcdir and deep/dir
2104 ac_srcdir='../../../package/deep/dir'
2108 independently of @samp{in/in.in}.
2111 Shell commands output @emph{unquoted} near the beginning of
2112 @file{config.status}, and executed each time @file{config.status} runs
2113 (regardless of the tag). Because they are unquoted, for example,
2114 @samp{$var} is output as the value of @code{var}. @var{init-cmds}
2115 is typically used by @file{configure} to give @file{config.status} some
2116 variables it needs to run the @var{commands}.
2118 You should be extremely cautious in your variable names: all the
2119 @var{init-cmds} share the same name space and may overwrite each other
2120 in unpredictable ways. Sorry@enddots{}
2123 All these macros can be called multiple times, with different
2124 @var{tag} values, of course!
2127 @node Configuration Files
2128 @section Creating Configuration Files
2129 @cindex Creating configuration files
2130 @cindex Configuration file creation
2132 Be sure to read the previous section, @ref{Configuration Actions}.
2134 @defmac AC_CONFIG_FILES (@var{file}@dots{}, @ovar{cmds}, @ovar{init-cmds})
2135 @acindex{CONFIG_FILES}
2136 Make @code{AC_OUTPUT} create each @file{@var{file}} by copying an input
2137 file (by default @file{@var{file}.in}), substituting the output variable
2139 @c Before we used to have this feature, which was later rejected
2140 @c because it complicates the writing of makefiles:
2141 @c If the file would be unchanged, it is left untouched, to preserve
2143 This macro is one of the instantiating macros; see @ref{Configuration
2144 Actions}. @xref{Makefile Substitutions}, for more information on using
2145 output variables. @xref{Setting Output Variables}, for more information
2146 on creating them. This macro creates the directory that the file is in
2147 if it doesn't exist. Usually, makefiles are created this way,
2148 but other files, such as @file{.gdbinit}, can be specified as well.
2150 Typical calls to @code{AC_CONFIG_FILES} look like this:
2153 AC_CONFIG_FILES([Makefile src/Makefile man/Makefile X/Imakefile])
2154 AC_CONFIG_FILES([autoconf], [chmod +x autoconf])
2157 You can override an input file name by appending to @var{file} a
2158 colon-separated list of input files. Examples:
2161 AC_CONFIG_FILES([Makefile:boiler/top.mk:boiler/bot.mk]
2162 [lib/Makefile:boiler/lib.mk])
2166 Doing this allows you to keep your file names acceptable to
2167 @acronym{DOS} variants, or
2168 to prepend and/or append boilerplate to the file.
2173 @node Makefile Substitutions
2174 @section Substitutions in Makefiles
2175 @cindex Substitutions in makefiles
2176 @cindex Makefile substitutions
2178 Each subdirectory in a distribution that contains something to be
2179 compiled or installed should come with a file @file{Makefile.in}, from
2180 which @command{configure} creates a file @file{Makefile} in that directory.
2181 To create @file{Makefile}, @command{configure} performs a simple variable
2182 substitution, replacing occurrences of @samp{@@@var{variable}@@} in
2183 @file{Makefile.in} with the value that @command{configure} has determined
2184 for that variable. Variables that are substituted into output files in
2185 this way are called @dfn{output variables}. They are ordinary shell
2186 variables that are set in @command{configure}. To make @command{configure}
2187 substitute a particular variable into the output files, the macro
2188 @code{AC_SUBST} must be called with that variable name as an argument.
2189 Any occurrences of @samp{@@@var{variable}@@} for other variables are
2190 left unchanged. @xref{Setting Output Variables}, for more information
2191 on creating output variables with @code{AC_SUBST}.
2193 A software package that uses a @command{configure} script should be
2194 distributed with a file @file{Makefile.in}, but no makefile; that
2195 way, the user has to properly configure the package for the local system
2196 before compiling it.
2198 @xref{Makefile Conventions, , Makefile Conventions, standards, The
2199 @acronym{GNU} Coding Standards}, for more information on what to put in
2203 * Preset Output Variables:: Output variables that are always set
2204 * Installation Directory Variables:: Other preset output variables
2205 * Changed Directory Variables:: Warnings about @file{datarootdir}
2206 * Build Directories:: Supporting multiple concurrent compiles
2207 * Automatic Remaking:: Makefile rules for configuring
2210 @node Preset Output Variables
2211 @subsection Preset Output Variables
2212 @cindex Output variables
2214 Some output variables are preset by the Autoconf macros. Some of the
2215 Autoconf macros set additional output variables, which are mentioned in
2216 the descriptions for those macros. @xref{Output Variable Index}, for a
2217 complete list of output variables. @xref{Installation Directory
2218 Variables}, for the list of the preset ones related to installation
2219 directories. Below are listed the other preset ones. They all are
2220 precious variables (@pxref{Setting Output Variables},
2223 @c Just say no to ASCII sorting! We're humans, not computers.
2224 @c These variables are listed as they would be in a dictionary:
2231 Debugging and optimization options for the C compiler. If it is not set
2232 in the environment when @command{configure} runs, the default value is set
2233 when you call @code{AC_PROG_CC} (or empty if you don't). @command{configure}
2234 uses this variable when compiling or linking programs to test for C features.
2236 If a compiler option affects only the behavior of the preprocessor
2237 (e.g., @option{-D @var{name}}), it should be put into @code{CPPFLAGS}
2238 instead. If it affects only the linker (e.g., @option{-L
2239 @var{directory}}), it should be put into @code{LDFLAGS} instead. If it
2240 affects only the compiler proper, @code{CFLAGS} is the natural home for
2241 it. If an option affects multiple phases of the compiler, though,
2242 matters get tricky. One approach to put such options directly into
2243 @code{CC}, e.g., @code{CC='gcc -m64'}. Another is to put them into both
2244 @code{CPPFLAGS} and @code{LDFLAGS}, but not into @code{CFLAGS}.
2248 @defvar configure_input
2249 @ovindex configure_input
2250 A comment saying that the file was generated automatically by
2251 @command{configure} and giving the name of the input file.
2252 @code{AC_OUTPUT} adds a comment line containing this variable to the top
2253 of every makefile it creates. For other files, you should
2254 reference this variable in a comment at the top of each input file. For
2255 example, an input shell script should begin like this:
2259 # @@configure_input@@
2263 The presence of that line also reminds people editing the file that it
2264 needs to be processed by @command{configure} in order to be used.
2269 Preprocessor options for the C, C++, and Objective C preprocessors and
2271 it is not set in the environment when @command{configure} runs, the default
2272 value is empty. @command{configure} uses this variable when preprocessing
2273 or compiling programs to test for C, C++, and Objective C features.
2275 This variable's contents should contain options like @option{-I},
2276 @option{-D}, and @option{-U} that affect only the behavior of the
2277 preprocessor. Please see the explanation of @code{CFLAGS} for what you
2278 can do if an option affects other phases of the compiler as well.
2280 Currently, @command{configure} always links as part of a single
2281 invocation of the compiler that also preprocesses and compiles, so it
2282 uses this variable also when linking programs. However, it is unwise to
2283 depend on this behavior because the @acronym{GNU} coding standards do
2284 not require it and many packages do not use @code{CPPFLAGS} when linking
2287 @xref{Special Chars in Variables}, for limitations that @code{CPPFLAGS}
2293 Debugging and optimization options for the C++ compiler. It acts like
2294 @code{CFLAGS}, but for C++ instead of C.
2299 @option{-D} options to pass to the C compiler. If @code{AC_CONFIG_HEADERS}
2300 is called, @command{configure} replaces @samp{@@DEFS@@} with
2301 @option{-DHAVE_CONFIG_H} instead (@pxref{Configuration Headers}). This
2302 variable is not defined while @command{configure} is performing its tests,
2303 only when creating the output files. @xref{Setting Output Variables}, for
2304 how to check the results of previous tests.
2313 How does one suppress the trailing newline from @command{echo} for
2314 question-answer message pairs? These variables provide a way:
2317 echo $ECHO_N "And the winner is... $ECHO_C"
2319 echo "$@{ECHO_T@}dead."
2323 Some old and uncommon @command{echo} implementations offer no means to
2324 achieve this, in which case @code{ECHO_T} is set to tab. You might not
2330 Debugging and optimization options for the Erlang compiler. If it is not set
2331 in the environment when @command{configure} runs, the default value is empty.
2332 @command{configure} uses this variable when compiling
2333 programs to test for Erlang features.
2338 Debugging and optimization options for the Fortran compiler. If it
2339 is not set in the environment when @command{configure} runs, the default
2340 value is set when you call @code{AC_PROG_FC} (or empty if you don't).
2341 @command{configure} uses this variable when compiling or linking
2342 programs to test for Fortran features.
2347 Debugging and optimization options for the Fortran 77 compiler. If it
2348 is not set in the environment when @command{configure} runs, the default
2349 value is set when you call @code{AC_PROG_F77} (or empty if you don't).
2350 @command{configure} uses this variable when compiling or linking
2351 programs to test for Fortran 77 features.
2356 Options for the linker. If it is not set
2357 in the environment when @command{configure} runs, the default value is empty.
2358 @command{configure} uses this variable when linking programs to test for
2359 C, C++, Objective C, and Fortran features.
2361 This variable's contents should contain options like @option{-s} and
2362 @option{-L} that affect only the behavior of the linker. Please see the
2363 explanation of @code{CFLAGS} for what you can do if an option also
2364 affects other phases of the compiler.
2366 Don't use this variable to pass library names
2367 (@option{-l}) to the linker; use @code{LIBS} instead.
2372 @option{-l} options to pass to the linker. The default value is empty,
2373 but some Autoconf macros may prepend extra libraries to this variable if
2374 those libraries are found and provide necessary functions, see
2375 @ref{Libraries}. @command{configure} uses this variable when linking
2376 programs to test for C, C++, and Fortran features.
2381 Debugging and optimization options for the Objective C compiler. It
2382 acts like @code{CFLAGS}, but for Objective C instead of C.
2387 Rigorously equal to @samp{.}. Added for symmetry only.
2390 @defvar abs_builddir
2391 @ovindex abs_builddir
2392 Absolute name of @code{builddir}.
2395 @defvar top_builddir
2396 @ovindex top_builddir
2397 The relative name of the top level of the current build tree. In the
2398 top-level directory, this is the same as @code{builddir}.
2401 @defvar abs_top_builddir
2402 @ovindex abs_top_builddir
2403 Absolute name of @code{top_builddir}.
2408 The name of the directory that contains the source code for
2414 Absolute name of @code{srcdir}.
2419 The name of the top-level source code directory for the
2420 package. In the top-level directory, this is the same as @code{srcdir}.
2423 @defvar abs_top_srcdir
2424 @ovindex abs_top_srcdir
2425 Absolute name of @code{top_srcdir}.
2428 @node Installation Directory Variables
2429 @subsection Installation Directory Variables
2430 @cindex Installation directories
2431 @cindex Directories, installation
2433 The following variables specify the directories for
2434 package installation, see @ref{Directory Variables, , Variables for
2435 Installation Directories, standards, The @acronym{GNU} Coding
2436 Standards}, for more information. See the end of this section for
2437 details on when and how to use these variables.
2441 The directory for installing executables that users run.
2446 The directory for installing idiosyncratic read-only
2447 architecture-independent data.
2451 @ovindex datarootdir
2452 The root of the directory tree for read-only architecture-independent
2458 The directory for installing documentation files (other than Info and
2464 The directory for installing documentation files in DVI format.
2468 @ovindex exec_prefix
2469 The installation prefix for architecture-dependent files. By default
2470 it's the same as @var{prefix}. You should avoid installing anything
2471 directly to @var{exec_prefix}. However, the default value for
2472 directories containing architecture-dependent files should be relative
2473 to @var{exec_prefix}.
2478 The directory for installing HTML documentation.
2483 The directory for installing C header files.
2488 The directory for installing documentation in Info format.
2493 The directory for installing object code libraries.
2498 The directory for installing executables that other programs run.
2503 The directory for installing locale-dependent but
2504 architecture-independent data, such as message catalogs. This directory
2505 usually has a subdirectory per locale.
2508 @defvar localstatedir
2509 @ovindex localstatedir
2510 The directory for installing modifiable single-machine data.
2515 The top-level directory for installing documentation in man format.
2518 @defvar oldincludedir
2519 @ovindex oldincludedir
2520 The directory for installing C header files for non-@acronym{GCC} compilers.
2525 The directory for installing PDF documentation.
2530 The common installation prefix for all files. If @var{exec_prefix}
2531 is defined to a different value, @var{prefix} is used only for
2532 architecture-independent files.
2537 The directory for installing PostScript documentation.
2542 The directory for installing executables that system
2546 @defvar sharedstatedir
2547 @ovindex sharedstatedir
2548 The directory for installing modifiable architecture-independent data.
2553 The directory for installing read-only single-machine data.
2557 Most of these variables have values that rely on @code{prefix} or
2558 @code{exec_prefix}. It is deliberate that the directory output
2559 variables keep them unexpanded: typically @samp{@@datarootdir@@} is
2560 replaced by @samp{$@{prefix@}/share}, not @samp{/usr/local/share}, and
2561 @samp{@@datadir@@} is replaced by @samp{$@{datarootdir@}}.
2563 This behavior is mandated by the @acronym{GNU} coding standards, so that when
2568 she can still specify a different prefix from the one specified to
2569 @command{configure}, in which case, if needed, the package should hard
2570 code dependencies corresponding to the make-specified prefix.
2573 she can specify a different installation location, in which case the
2574 package @emph{must} still depend on the location which was compiled in
2575 (i.e., never recompile when @samp{make install} is run). This is an
2576 extremely important feature, as many people may decide to install all
2577 the files of a package grouped together, and then install links from
2578 the final locations to there.
2581 In order to support these features, it is essential that
2582 @code{datarootdir} remains being defined as @samp{$@{prefix@}/share} to
2583 depend upon the current value of @code{prefix}.
2585 A corollary is that you should not use these variables except in
2586 makefiles. For instance, instead of trying to evaluate @code{datadir}
2587 in @file{configure} and hard-coding it in makefiles using
2588 e.g., @samp{AC_DEFINE_UNQUOTED([DATADIR], ["$datadir"], [Data directory.])},
2590 @option{-DDATADIR='$(datadir)'} to your makefile's definition of
2591 @code{CPPFLAGS} (@code{AM_CPPFLAGS} if you are also using Automake).
2593 Similarly, you should not rely on @code{AC_CONFIG_FILES} to replace
2594 @code{datadir} and friends in your shell scripts and other files; instead,
2595 let @command{make} manage their replacement. For instance Autoconf
2596 ships templates of its shell scripts ending with @samp{.in}, and uses a
2597 makefile snippet similar to the following to build scripts like
2598 @command{autoheader} and @command{autom4te}:
2603 -e 's|@@datadir[@@]|$(pkgdatadir)|g' \
2604 -e 's|@@prefix[@@]|$(prefix)|g'
2608 autoheader autom4te: Makefile
2610 $(edit) '$(srcdir)/$@@.in' >$@@.tmp
2617 autoheader: $(srcdir)/autoheader.in
2618 autom4te: $(srcdir)/autom4te.in
2622 Some details are noteworthy:
2625 @item @samp{@@datadir[@@]}
2626 The brackets prevent @command{configure} from replacing
2627 @samp{@@datadir@@} in the Sed expression itself.
2628 Brackets are preferable to a backslash here, since
2629 Posix says @samp{\@@} is not portable.
2631 @item @samp{$(pkgdatadir)}
2632 Don't use @samp{@@pkgdatadir@@}! Use the matching makefile variable
2636 Don't use @samp{/} in the Sed expressions that replace file names since
2638 variables you use, such as @samp{$(pkgdatadir)}, contain @samp{/}.
2639 Use a shell metacharacter instead, such as @samp{|}.
2641 @item special characters
2642 File names, file name components, and the value of @code{VPATH} should
2643 not contain shell metacharacters or white
2644 space. @xref{Special Chars in Variables}.
2646 @item dependency on @file{Makefile}
2647 Since @code{edit} uses values that depend on the configuration specific
2648 values (@code{prefix}, etc.)@: and not only on @code{VERSION} and so forth,
2649 the output depends on @file{Makefile}, not @file{configure.ac}.
2652 The main rule is generic, and uses @samp{$@@} extensively to
2653 avoid the need for multiple copies of the rule.
2655 @item Separated dependencies and single suffix rules
2656 You can't use them! The above snippet cannot be (portably) rewritten
2660 autoconf autoheader: Makefile
2670 @xref{Single Suffix Rules}, for details.
2672 @item @samp{$(srcdir)}
2673 Be sure to specify the name of the source directory,
2674 otherwise the package won't support separated builds.
2677 For the more specific installation of Erlang libraries, the following variables
2680 @defvar ERLANG_INSTALL_LIB_DIR
2681 @ovindex ERLANG_INSTALL_LIB_DIR
2682 @acindex{ERLANG_SUBST_INSTALL_LIB_DIR}
2683 The common parent directory of Erlang library installation directories.
2684 This variable is set by calling the @code{AC_ERLANG_SUBST_INSTALL_LIB_DIR}
2685 macro in @file{configure.ac}.
2688 @defvar ERLANG_INSTALL_LIB_DIR_@var{library}
2689 @ovindex ERLANG_INSTALL_LIB_DIR_@var{library}
2690 @acindex{ERLANG_SUBST_INSTALL_LIB_SUBDIR}
2691 The installation directory for Erlang library @var{library}.
2692 This variable is set by calling the
2693 @samp{AC_ERLANG_SUBST_INSTALL_LIB_SUBDIR(@var{library}, @var{version}}
2694 macro in @file{configure.ac}.
2697 @xref{Erlang Libraries}, for details.
2700 @node Changed Directory Variables
2701 @subsection Changed Directory Variables
2702 @cindex @file{datarootdir}
2704 In Autoconf 2.60, the set of directory variables has changed, and the
2705 defaults of some variables have been adjusted
2706 (@pxref{Installation Directory Variables}) to changes in the
2707 @acronym{GNU} Coding Standards. Notably, @file{datadir}, @file{infodir}, and
2708 @file{mandir} are now expressed in terms of @file{datarootdir}. If you are
2709 upgrading from an earlier Autoconf version, you may need to adjust your files
2710 to ensure that the directory variables are substituted correctly
2711 (@pxref{Defining Directories}), and that a definition of @file{datarootdir} is
2712 in place. For example, in a @file{Makefile.in}, adding
2715 datarootdir = @@datarootdir@@
2719 is usually sufficient. If you use Automake to create @file{Makefile.in},
2720 it will add this for you.
2722 To help with the transition, Autoconf warns about files that seem to use
2723 @code{datarootdir} without defining it. In some cases, it then expands
2724 the value of @code{$datarootdir} in substitutions of the directory
2725 variables. The following example shows such a warning:
2728 $ @kbd{cat configure.ac}
2730 AC_CONFIG_FILES([Makefile])
2732 $ @kbd{cat Makefile.in}
2734 datadir = @@datadir@@
2737 configure: creating ./config.status
2738 config.status: creating Makefile
2739 config.status: WARNING:
2740 Makefile.in seems to ignore the --datarootdir setting
2741 $ @kbd{cat Makefile}
2743 datadir = $@{prefix@}/share
2746 Usually one can easily change the file to accommodate both older and newer
2750 $ @kbd{cat Makefile.in}
2752 datarootdir = @@datarootdir@@
2753 datadir = @@datadir@@
2755 configure: creating ./config.status
2756 config.status: creating Makefile
2757 $ @kbd{cat Makefile}
2759 datarootdir = $@{prefix@}/share
2760 datadir = $@{datarootdir@}
2763 @acindex{DATAROOTDIR_CHECKED}
2764 In some cases, however, the checks may not be able to detect that a suitable
2765 initialization of @code{datarootdir} is in place, or they may fail to detect
2766 that such an initialization is necessary in the output file. If, after
2767 auditing your package, there are still spurious @file{configure} warnings about
2768 @code{datarootdir}, you may add the line
2771 AC_DEFUN([AC_DATAROOTDIR_CHECKED])
2775 to your @file{configure.ac} to disable the warnings. This is an exception
2776 to the usual rule that you should not define a macro whose name begins with
2777 @code{AC_} (@pxref{Macro Names}).
2781 @node Build Directories
2782 @subsection Build Directories
2783 @cindex Build directories
2784 @cindex Directories, build
2786 You can support compiling a software package for several architectures
2787 simultaneously from the same copy of the source code. The object files
2788 for each architecture are kept in their own directory.
2790 To support doing this, @command{make} uses the @code{VPATH} variable to
2791 find the files that are in the source directory. @acronym{GNU} Make
2792 can do this. Most other recent @command{make} programs can do this as
2793 well, though they may have difficulties and it is often simpler to
2794 recommend @acronym{GNU} @command{make} (@pxref{VPATH and Make}). Older
2795 @command{make} programs do not support @code{VPATH}; when using them, the
2796 source code must be in the same directory as the object files.
2798 To support @code{VPATH}, each @file{Makefile.in} should contain two
2799 lines that look like:
2806 Do not set @code{VPATH} to the value of another variable, for example
2807 @samp{VPATH = $(srcdir)}, because some versions of @command{make} do not do
2808 variable substitutions on the value of @code{VPATH}.
2810 @command{configure} substitutes the correct value for @code{srcdir} when
2811 it produces @file{Makefile}.
2813 Do not use the @code{make} variable @code{$<}, which expands to the
2814 file name of the file in the source directory (found with @code{VPATH}),
2815 except in implicit rules. (An implicit rule is one such as @samp{.c.o},
2816 which tells how to create a @file{.o} file from a @file{.c} file.) Some
2817 versions of @command{make} do not set @code{$<} in explicit rules; they
2818 expand it to an empty value.
2820 Instead, Make command lines should always refer to source
2821 files by prefixing them with @samp{$(srcdir)/}. For example:
2824 time.info: time.texinfo
2825 $(MAKEINFO) '$(srcdir)/time.texinfo'
2828 @node Automatic Remaking
2829 @subsection Automatic Remaking
2830 @cindex Automatic remaking
2831 @cindex Remaking automatically
2833 You can put rules like the following in the top-level @file{Makefile.in}
2834 for a package to automatically update the configuration information when
2835 you change the configuration files. This example includes all of the
2836 optional files, such as @file{aclocal.m4} and those related to
2837 configuration header files. Omit from the @file{Makefile.in} rules for
2838 any of these files that your package does not use.
2840 The @samp{$(srcdir)/} prefix is included because of limitations in the
2841 @code{VPATH} mechanism.
2843 The @file{stamp-} files are necessary because the timestamps of
2844 @file{config.h.in} and @file{config.h} are not changed if remaking
2845 them does not change their contents. This feature avoids unnecessary
2846 recompilation. You should include the file @file{stamp-h.in} your
2847 package's distribution, so that @command{make} considers
2848 @file{config.h.in} up to date. Don't use @command{touch}
2849 (@pxref{Limitations of Usual Tools}); instead, use @command{echo} (using
2850 @command{date} would cause needless differences, hence @acronym{CVS}
2855 $(srcdir)/configure: configure.ac aclocal.m4
2856 cd '$(srcdir)' && autoconf
2858 # autoheader might not change config.h.in, so touch a stamp file.
2859 $(srcdir)/config.h.in: stamp-h.in
2860 $(srcdir)/stamp-h.in: configure.ac aclocal.m4
2861 cd '$(srcdir)' && autoheader
2862 echo timestamp > '$(srcdir)/stamp-h.in'
2865 stamp-h: config.h.in config.status
2868 Makefile: Makefile.in config.status
2871 config.status: configure
2872 ./config.status --recheck
2877 (Be careful if you copy these lines directly into your makefile, as you
2878 need to convert the indented lines to start with the tab character.)
2880 In addition, you should use
2883 AC_CONFIG_FILES([stamp-h], [echo timestamp > stamp-h])
2887 so @file{config.status} ensures that @file{config.h} is considered up to
2888 date. @xref{Output}, for more information about @code{AC_OUTPUT}.
2890 @xref{config.status Invocation}, for more examples of handling
2891 configuration-related dependencies.
2893 @node Configuration Headers
2894 @section Configuration Header Files
2895 @cindex Configuration Header
2896 @cindex @file{config.h}
2898 When a package contains more than a few tests that define C preprocessor
2899 symbols, the command lines to pass @option{-D} options to the compiler
2900 can get quite long. This causes two problems. One is that the
2901 @command{make} output is hard to visually scan for errors. More
2902 seriously, the command lines can exceed the length limits of some
2903 operating systems. As an alternative to passing @option{-D} options to
2904 the compiler, @command{configure} scripts can create a C header file
2905 containing @samp{#define} directives. The @code{AC_CONFIG_HEADERS}
2906 macro selects this kind of output. Though it can be called anywhere
2907 between @code{AC_INIT} and @code{AC_OUTPUT}, it is customary to call
2908 it right after @code{AC_INIT}.
2910 The package should @samp{#include} the configuration header file before
2911 any other header files, to prevent inconsistencies in declarations (for
2912 example, if it redefines @code{const}).
2914 To provide for VPATH builds, remember to pass the C compiler a @option{-I.}
2915 option (or @option{-I..}; whichever directory contains @file{config.h}).
2916 Even if you use @samp{#include "config.h"}, the preprocessor searches only
2917 the directory of the currently read file, i.e., the source directory, not
2918 the build directory.
2920 With the appropriate @option{-I} option, you can use
2921 @samp{#include <config.h>}. Actually, it's a good habit to use it,
2922 because in the rare case when the source directory contains another
2923 @file{config.h}, the build directory should be searched first.
2926 @defmac AC_CONFIG_HEADERS (@var{header} @dots{}, @ovar{cmds}, @ovar{init-cmds})
2927 @acindex{CONFIG_HEADERS}
2928 @cvindex HAVE_CONFIG_H
2929 This macro is one of the instantiating macros; see @ref{Configuration
2930 Actions}. Make @code{AC_OUTPUT} create the file(s) in the
2931 blank-or-newline-separated list @var{header} containing C preprocessor
2932 @code{#define} statements, and replace @samp{@@DEFS@@} in generated
2933 files with @option{-DHAVE_CONFIG_H} instead of the value of @code{DEFS}.
2934 The usual name for @var{header} is @file{config.h}.
2936 If @var{header} already exists and its contents are identical to what
2937 @code{AC_OUTPUT} would put in it, it is left alone. Doing this allows
2938 making some changes in the configuration without needlessly causing
2939 object files that depend on the header file to be recompiled.
2941 Usually the input file is named @file{@var{header}.in}; however, you can
2942 override the input file name by appending to @var{header} a
2943 colon-separated list of input files. For example, you might need to make
2944 the input file name acceptable to @acronym{DOS} variants:
2947 AC_CONFIG_HEADERS([config.h:config.hin])
2954 This macro is defined as the name of the first declared config header
2955 and undefined if no config headers have been declared up to this point.
2956 A third-party macro may, for example, require use of a config header
2957 without invoking AC_CONFIG_HEADERS twice, like this:
2960 AC_CONFIG_COMMANDS_PRE(
2961 [m4_ifndef([AH_HEADER], [AC_CONFIG_HEADERS([config.h])])])
2966 @xref{Configuration Actions}, for more details on @var{header}.
2969 * Header Templates:: Input for the configuration headers
2970 * autoheader Invocation:: How to create configuration templates
2971 * Autoheader Macros:: How to specify CPP templates
2974 @node Header Templates
2975 @subsection Configuration Header Templates
2976 @cindex Configuration Header Template
2977 @cindex Header templates
2978 @cindex @file{config.h.in}
2980 Your distribution should contain a template file that looks as you want
2981 the final header file to look, including comments, with @code{#undef}
2982 statements which are used as hooks. For example, suppose your
2983 @file{configure.ac} makes these calls:
2986 AC_CONFIG_HEADERS([conf.h])
2987 AC_CHECK_HEADERS([unistd.h])
2991 Then you could have code like the following in @file{conf.h.in}. On
2992 systems that have @file{unistd.h}, @command{configure} defines
2993 @samp{HAVE_UNISTD_H} to 1. On other systems, the whole line is
2994 commented out (in case the system predefines that symbol).
2998 /* Define as 1 if you have unistd.h. */
2999 #undef HAVE_UNISTD_H
3003 Pay attention that @samp{#undef} is in the first column, and there is
3004 nothing after @samp{HAVE_UNISTD_H}, not even white space. You can
3005 then decode the configuration header using the preprocessor directives:
3011 #ifdef HAVE_UNISTD_H
3012 # include <unistd.h>
3014 /* We are in trouble. */
3019 The use of old form templates, with @samp{#define} instead of
3020 @samp{#undef} is strongly discouraged. Similarly with old templates
3021 with comments on the same line as the @samp{#undef}. Anyway, putting
3022 comments in preprocessor macros has never been a good idea.
3024 Since it is a tedious task to keep a template header up to date, you may
3025 use @command{autoheader} to generate it, see @ref{autoheader Invocation}.
3028 @node autoheader Invocation
3029 @subsection Using @command{autoheader} to Create @file{config.h.in}
3030 @cindex @command{autoheader}
3032 The @command{autoheader} program can create a template file of C
3033 @samp{#define} statements for @command{configure} to use.
3034 It searches for the first invocation of @code{AC_CONFIG_HEADERS} in
3035 @file{configure} sources to determine the name of the template.
3036 (If the first call of @code{AC_CONFIG_HEADERS} specifies more than one
3037 input file name, @command{autoheader} uses the first one.)
3039 It is recommended that only one input file is used. If you want to append
3040 a boilerplate code, it is preferable to use
3041 @samp{AH_BOTTOM([#include <conf_post.h>])}.
3042 File @file{conf_post.h} is not processed during the configuration then,
3043 which make things clearer. Analogically, @code{AH_TOP} can be used to
3044 prepend a boilerplate code.
3046 In order to do its job, @command{autoheader} needs you to document all
3047 of the symbols that you might use. Typically this is done via an
3048 @code{AC_DEFINE} or @code{AC_DEFINE_UNQUOTED} call whose first argument
3049 is a literal symbol and whose third argument describes the symbol
3050 (@pxref{Defining Symbols}). Alternatively, you can use
3051 @code{AH_TEMPLATE} (@pxref{Autoheader Macros}), or you can supply a
3052 suitable input file for a subsequent configuration header file.
3053 Symbols defined by Autoconf's builtin tests are already documented properly;
3054 you need to document only those that you
3057 You might wonder why @command{autoheader} is needed: after all, why
3058 would @command{configure} need to ``patch'' a @file{config.h.in} to
3059 produce a @file{config.h} instead of just creating @file{config.h} from
3060 scratch? Well, when everything rocks, the answer is just that we are
3061 wasting our time maintaining @command{autoheader}: generating
3062 @file{config.h} directly is all that is needed. When things go wrong,
3063 however, you'll be thankful for the existence of @command{autoheader}.
3065 The fact that the symbols are documented is important in order to
3066 @emph{check} that @file{config.h} makes sense. The fact that there is a
3067 well-defined list of symbols that should be defined (or not) is
3068 also important for people who are porting packages to environments where
3069 @command{configure} cannot be run: they just have to @emph{fill in the
3072 But let's come back to the point: the invocation of @command{autoheader}@dots{}
3074 If you give @command{autoheader} an argument, it uses that file instead
3075 of @file{configure.ac} and writes the header file to the standard output
3076 instead of to @file{config.h.in}. If you give @command{autoheader} an
3077 argument of @option{-}, it reads the standard input instead of
3078 @file{configure.ac} and writes the header file to the standard output.
3080 @command{autoheader} accepts the following options:
3085 Print a summary of the command line options and exit.
3089 Print the version number of Autoconf and exit.
3093 Report processing steps.
3097 Don't remove the temporary files.
3101 Remake the template file even if newer than its input files.
3103 @item --include=@var{dir}
3105 Append @var{dir} to the include path. Multiple invocations accumulate.
3107 @item --prepend-include=@var{dir}
3109 Prepend @var{dir} to the include path. Multiple invocations accumulate.
3111 @item --warnings=@var{category}
3112 @itemx -W @var{category}
3114 Report the warnings related to @var{category} (which can actually be a
3115 comma separated list). Current categories include:
3119 report the uses of obsolete constructs
3122 report all the warnings
3128 treats warnings as errors
3130 @item no-@var{category}
3131 disable warnings falling into @var{category}
3138 @node Autoheader Macros
3139 @subsection Autoheader Macros
3140 @cindex Autoheader macros
3142 @command{autoheader} scans @file{configure.ac} and figures out which C
3143 preprocessor symbols it might define. It knows how to generate
3144 templates for symbols defined by @code{AC_CHECK_HEADERS},
3145 @code{AC_CHECK_FUNCS} etc., but if you @code{AC_DEFINE} any additional
3146 symbol, you must define a template for it. If there are missing
3147 templates, @command{autoheader} fails with an error message.
3149 The template for a @var{symbol} is created
3150 by @command{autoheader} from
3151 the @var{description} argument to an @code{AC_DEFINE};
3152 see @ref{Defining Symbols}.
3154 For special needs, you can use the following macros.
3157 @defmac AH_TEMPLATE (@var{key}, @var{description})
3159 Tell @command{autoheader} to generate a template for @var{key}. This macro
3160 generates standard templates just like @code{AC_DEFINE} when a
3161 @var{description} is given.
3166 AH_TEMPLATE([CRAY_STACKSEG_END],
3167 [Define to one of _getb67, GETB67, getb67
3168 for Cray-2 and Cray-YMP systems. This
3169 function is required for alloca.c support
3174 generates the following template, with the description properly
3178 /* Define to one of _getb67, GETB67, getb67 for Cray-2 and
3179 Cray-YMP systems. This function is required for alloca.c
3180 support on those systems. */
3181 #undef CRAY_STACKSEG_END
3186 @defmac AH_VERBATIM (@var{key}, @var{template})
3188 Tell @command{autoheader} to include the @var{template} as-is in the header
3189 template file. This @var{template} is associated with the @var{key},
3190 which is used to sort all the different templates and guarantee their
3191 uniqueness. It should be a symbol that can be defined via @code{AC_DEFINE}.
3195 @defmac AH_TOP (@var{text})
3197 Include @var{text} at the top of the header template file.
3201 @defmac AH_BOTTOM (@var{text})
3203 Include @var{text} at the bottom of the header template file.
3207 Please note that @var{text} gets included ``verbatim'' to the template file,
3208 not to the resulting config header, so it can easily get mangled when the
3209 template is processed. There is rarely a need for something other than
3212 AH_BOTTOM([#include <custom.h>])
3217 @node Configuration Commands
3218 @section Running Arbitrary Configuration Commands
3219 @cindex Configuration commands
3220 @cindex Commands for configuration
3222 You can execute arbitrary commands before, during, and after
3223 @file{config.status} is run. The three following macros accumulate the
3224 commands to run when they are called multiple times.
3225 @code{AC_CONFIG_COMMANDS} replaces the obsolete macro
3226 @code{AC_OUTPUT_COMMANDS}; see @ref{Obsolete Macros}, for details.
3228 @defmac AC_CONFIG_COMMANDS (@var{tag}@dots{}, @ovar{cmds}, @ovar{init-cmds})
3229 @acindex{CONFIG_COMMANDS}
3230 Specify additional shell commands to run at the end of
3231 @file{config.status}, and shell commands to initialize any variables
3232 from @command{configure}. Associate the commands with @var{tag}.
3233 Since typically the @var{cmds} create a file, @var{tag} should
3234 naturally be the name of that file. If needed, the directory hosting
3235 @var{tag} is created. This macro is one of the instantiating macros;
3236 see @ref{Configuration Actions}.
3238 Here is an unrealistic example:
3241 AC_CONFIG_COMMANDS([fubar],
3242 [echo this is extra $fubar, and so on.],
3246 Here is a better one:
3248 AC_CONFIG_COMMANDS([timestamp], [date >timestamp])
3252 The following two macros look similar, but in fact they are not of the same
3253 breed: they are executed directly by @file{configure}, so you cannot use
3254 @file{config.status} to rerun them.
3256 @c Yet it is good to leave them here. The user sees them together and
3257 @c decides which best fits their needs.
3259 @defmac AC_CONFIG_COMMANDS_PRE (@var{cmds})
3260 @acindex{CONFIG_COMMANDS_PRE}
3261 Execute the @var{cmds} right before creating @file{config.status}.
3263 This macro presents the last opportunity to call @code{AC_SUBST},
3264 @code{AC_DEFINE}, or @code{AC_CONFIG_FOOS} macros.
3267 @defmac AC_CONFIG_COMMANDS_POST (@var{cmds})
3268 @acindex{CONFIG_COMMANDS_POST}
3269 Execute the @var{cmds} right after creating @file{config.status}.
3275 @node Configuration Links
3276 @section Creating Configuration Links
3277 @cindex Configuration links
3278 @cindex Links for configuration
3280 You may find it convenient to create links whose destinations depend upon
3281 results of tests. One can use @code{AC_CONFIG_COMMANDS} but the
3282 creation of relative symbolic links can be delicate when the package is
3283 built in a directory different from the source directory.
3285 @defmac AC_CONFIG_LINKS (@var{dest}:@var{source}@dots{}, @ovar{cmds}, @ovar{init-cmds})
3286 @acindex{CONFIG_LINKS}
3288 Make @code{AC_OUTPUT} link each of the existing files @var{source} to
3289 the corresponding link name @var{dest}. Makes a symbolic link if
3290 possible, otherwise a hard link if possible, otherwise a copy. The
3291 @var{dest} and @var{source} names should be relative to the top level
3292 source or build directory. This macro is one of the instantiating
3293 macros; see @ref{Configuration Actions}.
3295 For example, this call:
3298 AC_CONFIG_LINKS([host.h:config/$machine.h
3299 object.h:config/$obj_format.h])
3303 creates in the current directory @file{host.h} as a link to
3304 @file{@var{srcdir}/config/$machine.h}, and @file{object.h} as a
3305 link to @file{@var{srcdir}/config/$obj_format.h}.
3307 The tempting value @samp{.} for @var{dest} is invalid: it makes it
3308 impossible for @samp{config.status} to guess the links to establish.
3312 ./config.status host.h object.h
3315 to create the links.
3320 @node Subdirectories
3321 @section Configuring Other Packages in Subdirectories
3322 @cindex Configure subdirectories
3323 @cindex Subdirectory configure
3325 In most situations, calling @code{AC_OUTPUT} is sufficient to produce
3326 makefiles in subdirectories. However, @command{configure} scripts
3327 that control more than one independent package can use
3328 @code{AC_CONFIG_SUBDIRS} to run @command{configure} scripts for other
3329 packages in subdirectories.
3331 @defmac AC_CONFIG_SUBDIRS (@var{dir} @dots{})
3332 @acindex{CONFIG_SUBDIRS}
3334 Make @code{AC_OUTPUT} run @command{configure} in each subdirectory
3335 @var{dir} in the given blank-or-newline-separated list. Each @var{dir} should
3336 be a literal, i.e., please do not use:
3339 if test "$package_foo_enabled" = yes; then
3340 $my_subdirs="$my_subdirs foo"
3342 AC_CONFIG_SUBDIRS([$my_subdirs])
3346 because this prevents @samp{./configure --help=recursive} from
3347 displaying the options of the package @code{foo}. Instead, you should
3351 if test "$package_foo_enabled" = yes; then
3352 AC_CONFIG_SUBDIRS([foo])
3356 If a given @var{dir} is not found, an error is reported: if the
3357 subdirectory is optional, write:
3360 if test -d "$srcdir/foo"; then
3361 AC_CONFIG_SUBDIRS([foo])
3365 @c NB: Yes, below we mean configure.in, not configure.ac.
3366 If a given @var{dir} contains @command{configure.gnu}, it is run instead
3367 of @command{configure}. This is for packages that might use a
3368 non-Autoconf script @command{Configure}, which can't be called through a
3369 wrapper @command{configure} since it would be the same file on
3370 case-insensitive file systems. Likewise, if a @var{dir} contains
3371 @file{configure.in} but no @command{configure}, the Cygnus
3372 @command{configure} script found by @code{AC_CONFIG_AUX_DIR} is used.
3374 The subdirectory @command{configure} scripts are given the same command
3375 line options that were given to this @command{configure} script, with minor
3376 changes if needed, which include:
3380 adjusting a relative name for the cache file;
3383 adjusting a relative name for the source directory;
3386 propagating the current value of @code{$prefix}, including if it was
3387 defaulted, and if the default values of the top level and of the subdirectory
3388 @file{configure} differ.
3391 This macro also sets the output variable @code{subdirs} to the list of
3392 directories @samp{@var{dir} @dots{}}. Make rules can use
3393 this variable to determine which subdirectories to recurse into.
3395 This macro may be called multiple times.
3398 @node Default Prefix
3399 @section Default Prefix
3400 @cindex Install prefix
3401 @cindex Prefix for install
3403 By default, @command{configure} sets the prefix for files it installs to
3404 @file{/usr/local}. The user of @command{configure} can select a different
3405 prefix using the @option{--prefix} and @option{--exec-prefix} options.
3406 There are two ways to change the default: when creating
3407 @command{configure}, and when running it.
3409 Some software packages might want to install in a directory other than
3410 @file{/usr/local} by default. To accomplish that, use the
3411 @code{AC_PREFIX_DEFAULT} macro.
3413 @defmac AC_PREFIX_DEFAULT (@var{prefix})
3414 @acindex{PREFIX_DEFAULT}
3415 Set the default installation prefix to @var{prefix} instead of
3419 It may be convenient for users to have @command{configure} guess the
3420 installation prefix from the location of a related program that they
3421 have already installed. If you wish to do that, you can call
3422 @code{AC_PREFIX_PROGRAM}.
3424 @defmac AC_PREFIX_PROGRAM (@var{program})
3425 @acindex{PREFIX_PROGRAM}
3426 If the user did not specify an installation prefix (using the
3427 @option{--prefix} option), guess a value for it by looking for
3428 @var{program} in @env{PATH}, the way the shell does. If @var{program}
3429 is found, set the prefix to the parent of the directory containing
3430 @var{program}, else default the prefix as described above
3431 (@file{/usr/local} or @code{AC_PREFIX_DEFAULT}). For example, if
3432 @var{program} is @code{gcc} and the @env{PATH} contains
3433 @file{/usr/local/gnu/bin/gcc}, set the prefix to @file{/usr/local/gnu}.
3438 @c ======================================================== Existing tests
3440 @node Existing Tests
3441 @chapter Existing Tests
3443 These macros test for particular system features that packages might
3444 need or want to use. If you need to test for a kind of feature that
3445 none of these macros check for, you can probably do it by calling
3446 primitive test macros with appropriate arguments (@pxref{Writing
3449 These tests print messages telling the user which feature they're
3450 checking for, and what they find. They cache their results for future
3451 @command{configure} runs (@pxref{Caching Results}).
3453 Some of these macros set output variables. @xref{Makefile
3454 Substitutions}, for how to get their values. The phrase ``define
3455 @var{name}'' is used below as a shorthand to mean ``define the C
3456 preprocessor symbol @var{name} to the value 1''. @xref{Defining
3457 Symbols}, for how to get those symbol definitions into your program.
3460 * Common Behavior:: Macros' standard schemes
3461 * Alternative Programs:: Selecting between alternative programs
3462 * Files:: Checking for the existence of files
3463 * Libraries:: Library archives that might be missing
3464 * Library Functions:: C library functions that might be missing
3465 * Header Files:: Header files that might be missing
3466 * Declarations:: Declarations that may be missing
3467 * Structures:: Structures or members that might be missing
3468 * Types:: Types that might be missing
3469 * Compilers and Preprocessors:: Checking for compiling programs
3470 * System Services:: Operating system services
3471 * Posix Variants:: Special kludges for specific Posix variants
3472 * Erlang Libraries:: Checking for the existence of Erlang libraries
3475 @node Common Behavior
3476 @section Common Behavior
3477 @cindex Common autoconf behavior
3479 Much effort has been expended to make Autoconf easy to learn. The most
3480 obvious way to reach this goal is simply to enforce standard interfaces
3481 and behaviors, avoiding exceptions as much as possible. Because of
3482 history and inertia, unfortunately, there are still too many exceptions
3483 in Autoconf; nevertheless, this section describes some of the common
3487 * Standard Symbols:: Symbols defined by the macros
3488 * Default Includes:: Includes used by the generic macros
3491 @node Standard Symbols
3492 @subsection Standard Symbols
3493 @cindex Standard symbols
3495 All the generic macros that @code{AC_DEFINE} a symbol as a result of
3496 their test transform their @var{argument} values to a standard alphabet.
3497 First, @var{argument} is converted to upper case and any asterisks
3498 (@samp{*}) are each converted to @samp{P}. Any remaining characters
3499 that are not alphanumeric are converted to underscores.
3504 AC_CHECK_TYPES([struct $Expensive*])
3508 defines the symbol @samp{HAVE_STRUCT__EXPENSIVEP} if the check
3512 @node Default Includes
3513 @subsection Default Includes
3514 @cindex Default includes
3515 @cindex Includes, default
3517 Several tests depend upon a set of header files. Since these headers
3518 are not universally available, tests actually have to provide a set of
3519 protected includes, such as:
3523 #ifdef TIME_WITH_SYS_TIME
3524 # include <sys/time.h>
3527 # ifdef HAVE_SYS_TIME_H
3528 # include <sys/time.h>
3537 Unless you know exactly what you are doing, you should avoid using
3538 unconditional includes, and check the existence of the headers you
3539 include beforehand (@pxref{Header Files}).
3541 Most generic macros use the following macro to provide the default set
3544 @defmac AC_INCLUDES_DEFAULT (@ovar{include-directives})
3545 @acindex{INCLUDES_DEFAULT}
3546 Expand to @var{include-directives} if defined, otherwise to:
3551 #ifdef HAVE_SYS_TYPES_H
3552 # include <sys/types.h>
3554 #ifdef HAVE_SYS_STAT_H
3555 # include <sys/stat.h>
3558 # include <stdlib.h>
3559 # include <stddef.h>
3561 # ifdef HAVE_STDLIB_H
3562 # include <stdlib.h>
3565 #ifdef HAVE_STRING_H
3566 # if !defined STDC_HEADERS && defined HAVE_MEMORY_H
3567 # include <memory.h>
3569 # include <string.h>
3571 #ifdef HAVE_STRINGS_H
3572 # include <strings.h>
3574 #ifdef HAVE_INTTYPES_H
3575 # include <inttypes.h>
3577 #ifdef HAVE_STDINT_H
3578 # include <stdint.h>
3580 #ifdef HAVE_UNISTD_H
3581 # include <unistd.h>
3586 If the default includes are used, then check for the presence of these
3587 headers and their compatibility, i.e., you don't need to run
3588 @code{AC_HEADER_STDC}, nor check for @file{stdlib.h} etc.
3590 These headers are checked for in the same order as they are included.
3591 For instance, on some systems @file{string.h} and @file{strings.h} both
3592 exist, but conflict. Then @code{HAVE_STRING_H} is defined, not
3593 @code{HAVE_STRINGS_H}.
3596 @node Alternative Programs
3597 @section Alternative Programs
3598 @cindex Programs, checking
3600 These macros check for the presence or behavior of particular programs.
3601 They are used to choose between several alternative programs and to
3602 decide what to do once one has been chosen. If there is no macro
3603 specifically defined to check for a program you need, and you don't need
3604 to check for any special properties of it, then you can use one of the
3605 general program-check macros.
3608 * Particular Programs:: Special handling to find certain programs
3609 * Generic Programs:: How to find other programs
3612 @node Particular Programs
3613 @subsection Particular Program Checks
3615 These macros check for particular programs---whether they exist, and
3616 in some cases whether they support certain features.
3621 Check for @code{gawk}, @code{mawk}, @code{nawk}, and @code{awk}, in that
3622 order, and set output variable @code{AWK} to the first one that is found.
3623 It tries @code{gawk} first because that is reported to be the
3624 best implementation.
3627 @defmac AC_PROG_GREP
3630 Look for the best available @code{grep} or @code{ggrep} that accepts the
3631 longest input lines possible, and that supports multiple @option{-e} options.
3632 Set the output variable @code{GREP} to whatever is chosen.
3633 @xref{Limitations of Usual Tools}, for more information about
3634 portability problems with the @command{grep} command family.
3637 @defmac AC_PROG_EGREP
3638 @acindex{PROG_EGREP}
3640 Check whether @code{$GREP -E} works, or else look for the best available
3641 @code{egrep} or @code{gegrep} that accepts the longest input lines possible.
3642 Set the output variable @code{EGREP} to whatever is chosen.
3645 @defmac AC_PROG_FGREP
3646 @acindex{PROG_FGREP}
3648 Check whether @code{$GREP -F} works, or else look for the best available
3649 @code{fgrep} or @code{gfgrep} that accepts the longest input lines possible.
3650 Set the output variable @code{FGREP} to whatever is chosen.
3653 @defmac AC_PROG_INSTALL
3654 @acindex{PROG_INSTALL}
3656 @ovindex INSTALL_PROGRAM
3657 @ovindex INSTALL_DATA
3658 @ovindex INSTALL_SCRIPT
3659 Set output variable @code{INSTALL} to the name of a @acronym{BSD}-compatible
3660 @command{install} program, if one is found in the current @env{PATH}.
3661 Otherwise, set @code{INSTALL} to @samp{@var{dir}/install-sh -c},
3662 checking the directories specified to @code{AC_CONFIG_AUX_DIR} (or its
3663 default directories) to determine @var{dir} (@pxref{Output}). Also set
3664 the variables @code{INSTALL_PROGRAM} and @code{INSTALL_SCRIPT} to
3665 @samp{$@{INSTALL@}} and @code{INSTALL_DATA} to @samp{$@{INSTALL@} -m 644}.
3667 @samp{@@INSTALL@@} is special, as its value may vary for different
3668 configuration files.
3670 This macro screens out various instances of @command{install} known not to
3671 work. It prefers to find a C program rather than a shell script, for
3672 speed. Instead of @file{install-sh}, it can also use @file{install.sh},
3673 but that name is obsolete because some @command{make} programs have a rule
3674 that creates @file{install} from it if there is no makefile.
3676 Autoconf comes with a copy of @file{install-sh} that you can use. If
3677 you use @code{AC_PROG_INSTALL}, you must include either
3678 @file{install-sh} or @file{install.sh} in your distribution; otherwise
3679 @command{configure} produces an error message saying it can't find
3680 them---even if the system you're on has a good @command{install} program.
3681 This check is a safety measure to prevent you from accidentally leaving
3682 that file out, which would prevent your package from installing on
3683 systems that don't have a @acronym{BSD}-compatible @command{install} program.
3685 If you need to use your own installation program because it has features
3686 not found in standard @command{install} programs, there is no reason to use
3687 @code{AC_PROG_INSTALL}; just put the file name of your program into your
3688 @file{Makefile.in} files.
3691 @defmac AC_PROG_MKDIR_P
3692 @acindex{PROG_MKDIR_P}
3694 Set output variable @code{MKDIR_P} to a program that ensures that for
3695 each argument, a directory named by this argument exists, creating it
3696 and its parent directories if needed, and without race conditions when
3697 two instances of the program attempt to make the same directory at
3698 nearly the same time.
3700 This macro uses the @samp{mkdir -p} command if possible. Otherwise, it
3701 falls back on invoking @command{install-sh} with the @option{-d} option,
3702 so your package should
3703 contain @file{install-sh} as described under @code{AC_PROG_INSTALL}.
3704 An @file{install-sh} file that predates Autoconf 2.60 or Automake 1.10
3705 is vulnerable to race conditions, so if you want to support parallel
3707 different packages into the same directory you need to make sure you
3708 have an up-to-date @file{install-sh}. In particular, be careful about
3709 using @samp{autoreconf -if} if your Automake predates Automake 1.10.
3711 This macro is related to the @code{AS_MKDIR_P} macro (@pxref{Programming
3712 in M4sh}), but it sets an output variable intended for use in other
3713 files, whereas @code{AS_MKDIR_P} is intended for use in scripts like
3714 @command{configure}. Also, @code{AS_MKDIR_P} does not accept options,
3715 but @code{MKDIR_P} supports the @option{-m} option, e.g., a makefile
3716 might invoke @code{$(MKDIR_P) -m 0 dir} to create an inaccessible
3717 directory, and conversely a makefile should use @code{$(MKDIR_P) --
3718 $(FOO)} if @var{FOO} might yield a value that begins with @samp{-}.
3719 Finally, @code{AS_MKDIR_P} does not check for race condition
3720 vulnerability, whereas @code{AC_PROG_MKDIR_P} does.
3722 @samp{@@MKDIR_P@@} is special, as its value may vary for different
3723 configuration files.
3730 @cvindex YYTEXT_POINTER
3731 @ovindex LEX_OUTPUT_ROOT
3732 If @code{flex} is found, set output variable @code{LEX} to @samp{flex}
3733 and @code{LEXLIB} to @option{-lfl}, if that library is in a standard
3734 place. Otherwise set @code{LEX} to @samp{lex} and @code{LEXLIB} to
3737 Define @code{YYTEXT_POINTER} if @code{yytext} defaults to @samp{char *} instead
3738 of to @samp{char []}. Also set output variable @code{LEX_OUTPUT_ROOT} to
3739 the base of the file name that the lexer generates; usually
3740 @file{lex.yy}, but sometimes something else. These results vary
3741 according to whether @code{lex} or @code{flex} is being used.
3743 You are encouraged to use Flex in your sources, since it is both more
3744 pleasant to use than plain Lex and the C source it produces is portable.
3745 In order to ensure portability, however, you must either provide a
3746 function @code{yywrap} or, if you don't use it (e.g., your scanner has
3747 no @samp{#include}-like feature), simply include a @samp{%noyywrap}
3748 statement in the scanner's source. Once this done, the scanner is
3749 portable (unless @emph{you} felt free to use nonportable constructs) and
3750 does not depend on any library. In this case, and in this case only, it
3751 is suggested that you use this Autoconf snippet:
3755 if test "$LEX" != flex; then
3756 LEX="$SHELL $missing_dir/missing flex"
3757 AC_SUBST([LEX_OUTPUT_ROOT], [lex.yy])
3758 AC_SUBST([LEXLIB], [''])
3762 The shell script @command{missing} can be found in the Automake
3765 To ensure backward compatibility, Automake's @code{AM_PROG_LEX} invokes
3766 (indirectly) this macro twice, which causes an annoying but benign
3767 ``@code{AC_PROG_LEX} invoked multiple times'' warning. Future versions
3768 of Automake will fix this issue; meanwhile, just ignore this message.
3770 As part of running the test, this macro may delete any file in the
3771 configuration directory named @file{lex.yy.c} or @file{lexyy.c}.
3774 @defmac AC_PROG_LN_S
3777 If @samp{ln -s} works on the current file system (the operating system
3778 and file system support symbolic links), set the output variable
3779 @code{LN_S} to @samp{ln -s}; otherwise, if @samp{ln} works, set
3780 @code{LN_S} to @samp{ln}, and otherwise set it to @samp{cp -p}.
3782 If you make a link in a directory other than the current directory, its
3783 meaning depends on whether @samp{ln} or @samp{ln -s} is used. To safely
3784 create links using @samp{$(LN_S)}, either find out which form is used
3785 and adjust the arguments, or always invoke @code{ln} in the directory
3786 where the link is to be created.
3788 In other words, it does not work to do:
3796 (cd /x && $(LN_S) foo bar)
3800 @defmac AC_PROG_RANLIB
3801 @acindex{PROG_RANLIB}
3803 Set output variable @code{RANLIB} to @samp{ranlib} if @code{ranlib}
3804 is found, and otherwise to @samp{:} (do nothing).
3810 Set output variable @code{SED} to a Sed implementation that conforms to
3811 Posix and does not have arbitrary length limits. Report an error if no
3812 acceptable Sed is found. @xref{Limitations of Usual Tools}, for more
3813 information about portability problems with Sed.
3816 @defmac AC_PROG_YACC
3819 If @code{bison} is found, set output variable @code{YACC} to @samp{bison
3820 -y}. Otherwise, if @code{byacc} is found, set @code{YACC} to
3821 @samp{byacc}. Otherwise set @code{YACC} to @samp{yacc}.
3824 @node Generic Programs
3825 @subsection Generic Program and File Checks
3827 These macros are used to find programs not covered by the ``particular''
3828 test macros. If you need to check the behavior of a program as well as
3829 find out whether it is present, you have to write your own test for it
3830 (@pxref{Writing Tests}). By default, these macros use the environment
3831 variable @env{PATH}. If you need to check for a program that might not
3832 be in the user's @env{PATH}, you can pass a modified path to use
3836 AC_PATH_PROG([INETD], [inetd], [/usr/libexec/inetd],
3837 [$PATH:/usr/libexec:/usr/sbin:/usr/etc:/etc])
3840 You are strongly encouraged to declare the @var{variable} passed to
3841 @code{AC_CHECK_PROG} etc.@: as precious, @xref{Setting Output Variables},
3842 @code{AC_ARG_VAR}, for more details.
3844 @defmac AC_CHECK_PROG (@var{variable}, @var{prog-to-check-for}, @var{value-if-found}, @ovar{value-if-not-found}, @ovar{path}, @ovar{reject})
3845 @acindex{CHECK_PROG}
3846 Check whether program @var{prog-to-check-for} exists in @env{PATH}. If
3847 it is found, set @var{variable} to @var{value-if-found}, otherwise to
3848 @var{value-if-not-found}, if given. Always pass over @var{reject} (an
3849 absolute file name) even if it is the first found in the search path; in
3850 that case, set @var{variable} using the absolute file name of the
3851 @var{prog-to-check-for} found that is not @var{reject}. If
3852 @var{variable} was already set, do nothing. Calls @code{AC_SUBST} for
3856 @defmac AC_CHECK_PROGS (@var{variable}, @var{progs-to-check-for}, @ovar{value-if-not-found}, @ovar{path})
3857 @acindex{CHECK_PROGS}
3858 Check for each program in the blank-separated list
3859 @var{progs-to-check-for} existing in the @env{PATH}. If one is found, set
3860 @var{variable} to the name of that program. Otherwise, continue
3861 checking the next program in the list. If none of the programs in the
3862 list are found, set @var{variable} to @var{value-if-not-found}; if
3863 @var{value-if-not-found} is not specified, the value of @var{variable}
3864 is not changed. Calls @code{AC_SUBST} for @var{variable}.
3867 @defmac AC_CHECK_TARGET_TOOL (@var{variable}, @var{prog-to-check-for}, @ovar{value-if-not-found}, @ovar{path})
3868 @acindex{CHECK_TARGET_TOOL}
3869 Like @code{AC_CHECK_PROG}, but first looks for @var{prog-to-check-for}
3870 with a prefix of the target type as determined by
3871 @code{AC_CANONICAL_TARGET}, followed by a dash (@pxref{Canonicalizing}).
3872 If the tool cannot be found with a prefix, and if the build and target
3873 types are equal, then it is also searched for without a prefix.
3875 As noted in @ref{Specifying Names, , Specifying the system type}, the
3876 target is rarely specified, because most of the time it is the same
3877 as the host: it is the type of system for which any compiler tool in
3878 the package produces code. What this macro looks for is,
3879 for example, @emph{a tool @r{(assembler, linker, etc.)}@: that the
3880 compiler driver @r{(@command{gcc} for the @acronym{GNU} C Compiler)}
3881 uses to produce objects, archives or executables}.
3884 @defmac AC_CHECK_TOOL (@var{variable}, @var{prog-to-check-for}, @ovar{value-if-not-found}, @ovar{path})
3885 @acindex{CHECK_TOOL}
3886 Like @code{AC_CHECK_PROG}, but first looks for @var{prog-to-check-for}
3887 with a prefix of the host type as determined by
3888 @code{AC_CANONICAL_HOST}, followed by a dash (@pxref{Canonicalizing}).
3889 For example, if the user runs @samp{configure --host=i386-gnu}, then
3892 AC_CHECK_TOOL([RANLIB], [ranlib], [:])
3895 sets @code{RANLIB} to @file{i386-gnu-ranlib} if that program exists in
3896 @env{PATH}, or otherwise to @samp{ranlib} if that program exists in
3897 @env{PATH}, or to @samp{:} if neither program exists.
3899 In the future, when cross-compiling this macro will @emph{only}
3900 accept program names that are prefixed with the host type.
3901 For more information, see @ref{Specifying Names, , Specifying the
3905 @defmac AC_CHECK_TARGET_TOOLS (@var{variable}, @var{progs-to-check-for}, @ovar{value-if-not-found}, @ovar{path})
3906 @acindex{CHECK_TARGET_TOOLS}
3907 Like @code{AC_CHECK_TARGET_TOOL}, each of the tools in the list
3908 @var{progs-to-check-for} are checked with a prefix of the target type as
3909 determined by @code{AC_CANONICAL_TARGET}, followed by a dash
3910 (@pxref{Canonicalizing}). If none of the tools can be found with a
3911 prefix, and if the build and target types are equal, then the first one
3912 without a prefix is used. If a tool is found, set @var{variable} to
3913 the name of that program. If none of the tools in the list are found,
3914 set @var{variable} to @var{value-if-not-found}; if @var{value-if-not-found}
3915 is not specified, the value of @var{variable} is not changed. Calls
3916 @code{AC_SUBST} for @var{variable}.
3919 @defmac AC_CHECK_TOOLS (@var{variable}, @var{progs-to-check-for}, @ovar{value-if-not-found}, @ovar{path})
3920 @acindex{CHECK_TOOLS}
3921 Like @code{AC_CHECK_TOOL}, each of the tools in the list
3922 @var{progs-to-check-for} are checked with a prefix of the host type as
3923 determined by @code{AC_CANONICAL_HOST}, followed by a dash
3924 (@pxref{Canonicalizing}). If none of the tools can be found with a
3925 prefix, then the first one without a prefix is used. If a tool is found,
3926 set @var{variable} to the name of that program. If none of the tools in
3927 the list are found, set @var{variable} to @var{value-if-not-found}; if
3928 @var{value-if-not-found} is not specified, the value of @var{variable}
3929 is not changed. Calls @code{AC_SUBST} for @var{variable}.
3931 In the future, when cross-compiling this macro will @emph{not}
3932 accept program names that are not prefixed with the host type.
3935 @defmac AC_PATH_PROG (@var{variable}, @var{prog-to-check-for}, @ovar{value-if-not-found}, @ovar{path})
3937 Like @code{AC_CHECK_PROG}, but set @var{variable} to the absolute
3938 name of @var{prog-to-check-for} if found.
3941 @defmac AC_PATH_PROGS (@var{variable}, @var{progs-to-check-for}, @ovar{value-if-not-found}, @ovar{path})
3942 @acindex{PATH_PROGS}
3943 Like @code{AC_CHECK_PROGS}, but if any of @var{progs-to-check-for}
3944 are found, set @var{variable} to the absolute name of the program
3948 @defmac AC_PATH_TARGET_TOOL (@var{variable}, @var{prog-to-check-for}, @ovar{value-if-not-found}, @ovar{path})
3949 @acindex{PATH_TARGET_TOOL}
3950 Like @code{AC_CHECK_TARGET_TOOL}, but set @var{variable} to the absolute
3951 name of the program if it is found.
3954 @defmac AC_PATH_TOOL (@var{variable}, @var{prog-to-check-for}, @ovar{value-if-not-found}, @ovar{path})
3956 Like @code{AC_CHECK_TOOL}, but set @var{variable} to the absolute
3957 name of the program if it is found.
3959 In the future, when cross-compiling this macro will @emph{not}
3960 accept program names that are not prefixed with the host type.
3966 @cindex File, checking
3968 You might also need to check for the existence of files. Before using
3969 these macros, ask yourself whether a runtime test might not be a better
3970 solution. Be aware that, like most Autoconf macros, they test a feature
3971 of the host machine, and therefore, they die when cross-compiling.
3973 @defmac AC_CHECK_FILE (@var{file}, @ovar{action-if-found}, @ovar{action-if-not-found})
3974 @acindex{CHECK_FILE}
3975 Check whether file @var{file} exists on the native system. If it is
3976 found, execute @var{action-if-found}, otherwise do
3977 @var{action-if-not-found}, if given.
3980 @defmac AC_CHECK_FILES (@var{files}, @ovar{action-if-found}, @ovar{action-if-not-found})
3981 @acindex{CHECK_FILES}
3982 Executes @code{AC_CHECK_FILE} once for each file listed in @var{files}.
3983 Additionally, defines @samp{HAVE_@var{file}} (@pxref{Standard Symbols})
3984 for each file found.
3989 @section Library Files
3990 @cindex Library, checking
3992 The following macros check for the presence of certain C, C++, or Fortran
3993 library archive files.
3995 @defmac AC_CHECK_LIB (@var{library}, @var{function}, @ovar{action-if-found}, @ovar{action-if-not-found}, @ovar{other-libraries})
3997 Test whether the library @var{library} is available by trying to link
3998 a test program that calls function @var{function} with the library.
3999 @var{function} should be a function provided by the library.
4001 name of the library; e.g., to check for @option{-lmp}, use @samp{mp} as
4002 the @var{library} argument.
4004 @var{action-if-found} is a list of shell commands to run if the link
4005 with the library succeeds; @var{action-if-not-found} is a list of shell
4006 commands to run if the link fails. If @var{action-if-found} is not
4007 specified, the default action prepends @option{-l@var{library}} to
4008 @code{LIBS} and defines @samp{HAVE_LIB@var{library}} (in all
4009 capitals). This macro is intended to support building @code{LIBS} in
4010 a right-to-left (least-dependent to most-dependent) fashion such that
4011 library dependencies are satisfied as a natural side effect of
4012 consecutive tests. Linkers are sensitive to library ordering
4013 so the order in which @code{LIBS} is generated is important to reliable
4014 detection of libraries.
4016 If linking with @var{library} results in unresolved symbols that would
4017 be resolved by linking with additional libraries, give those libraries
4018 as the @var{other-libraries} argument, separated by spaces:
4019 e.g., @option{-lXt -lX11}. Otherwise, this macro fails to detect
4020 that @var{library} is present, because linking the test program
4021 always fails with unresolved symbols. The @var{other-libraries} argument
4022 should be limited to cases where it is desirable to test for one library
4023 in the presence of another that is not already in @code{LIBS}.
4025 @code{AC_CHECK_LIB} requires some care in usage, and should be avoided
4026 in some common cases. Many standard functions like @code{gethostbyname}
4027 appear in the standard C library on some hosts, and in special libraries
4028 like @code{nsl} on other hosts. On some hosts the special libraries
4029 contain variant implementations that you may not want to use. These
4030 days it is normally better to use @code{AC_SEARCH_LIBS([gethostbyname],
4031 [nsl])} instead of @code{AC_CHECK_LIB([nsl], [gethostbyname])}.
4035 @defmac AC_SEARCH_LIBS (@var{function}, @var{search-libs}, @ovar{action-if-found}, @ovar{action-if-not-found}, @ovar{other-libraries})
4036 @acindex{SEARCH_LIBS}
4037 Search for a library defining @var{function} if it's not already
4038 available. This equates to calling
4039 @samp{AC_LINK_IFELSE([AC_LANG_CALL([], [@var{function}])])} first with
4040 no libraries, then for each library listed in @var{search-libs}.
4042 Add @option{-l@var{library}} to @code{LIBS} for the first library found
4043 to contain @var{function}, and run @var{action-if-found}. If the
4044 function is not found, run @var{action-if-not-found}.
4046 If linking with @var{library} results in unresolved symbols that would
4047 be resolved by linking with additional libraries, give those libraries
4048 as the @var{other-libraries} argument, separated by spaces:
4049 e.g., @option{-lXt -lX11}. Otherwise, this macro fails to detect
4050 that @var{function} is present, because linking the test program
4051 always fails with unresolved symbols.
4056 @node Library Functions
4057 @section Library Functions
4059 The following macros check for particular C library functions.
4060 If there is no macro specifically defined to check for a function you need,
4061 and you don't need to check for any special properties of
4062 it, then you can use one of the general function-check macros.
4065 * Function Portability:: Pitfalls with usual functions
4066 * Particular Functions:: Special handling to find certain functions
4067 * Generic Functions:: How to find other functions
4070 @node Function Portability
4071 @subsection Portability of C Functions
4072 @cindex Portability of C functions
4073 @cindex C function portability
4075 Most usual functions can either be missing, or be buggy, or be limited
4076 on some architectures. This section tries to make an inventory of these
4077 portability issues. By definition, this list always requires
4078 additions. Please help us keeping it as complete as possible.
4083 @prindex @code{exit}
4084 On ancient hosts, @code{exit} returned @code{int}.
4085 This is because @code{exit} predates @code{void}, and there was a long
4086 tradition of it returning @code{int}.
4088 On current hosts, the problem more likely is that @code{exit} is not
4089 declared, due to C++ problems of some sort or another. For this reason
4090 we suggest that test programs not invoke @code{exit}, but return from
4091 @code{main} instead.
4095 @prindex @code{free}
4096 The C standard says a call @code{free (NULL)} does nothing, but
4097 some old systems don't support this (e.g., NextStep).
4103 @prindex @code{isinf}
4104 @prindex @code{isnan}
4105 The C99 standard says that @code{isinf} and @code{isnan} are
4106 macros. On some systems just macros are available
4107 (e.g., @acronym{HP-UX} and Solaris 10), on
4108 some systems both macros and functions (e.g., glibc 2.3.2), and on some
4109 systems only functions (e.g., IRIX 6 and Solaris 9). In some cases
4110 these functions are declared in nonstandard headers like
4111 @code{<sunmath.h>} and defined in non-default libraries like
4112 @option{-lm} or @option{-lsunmath}.
4114 The C99 @code{isinf} and @code{isnan} macros work correctly with
4115 @code{long double} arguments, but pre-C99 systems that use functions
4116 typically assume @code{double} arguments. On such a system,
4117 @code{isinf} incorrectly returns true for a finite @code{long double}
4118 argument that is outside the range of @code{double}.
4120 To work around this porting mess, you can use code like the following.
4127 (sizeof (x) == sizeof (long double) ? isnan_ld (x) \
4128 : sizeof (x) == sizeof (double) ? isnan_d (x) \
4130 static inline int isnan_f (float x) @{ return x != x; @}
4131 static inline int isnan_d (double x) @{ return x != x; @}
4132 static inline int isnan_ld (long double x) @{ return x != x; @}
4137 (sizeof (x) == sizeof (long double) ? isinf_ld (x) \
4138 : sizeof (x) == sizeof (double) ? isinf_d (x) \
4140 static inline int isinf_f (float x) @{ return isnan (x - x); @}
4141 static inline int isinf_d (double x) @{ return isnan (x - x); @}
4142 static inline int isinf_ld (long double x) @{ return isnan (x - x); @}
4146 Use @code{AC_C_INLINE} (@pxref{C Compiler}) so that this code works on
4147 compilers that lack the @code{inline} keyword. Some optimizing
4148 compilers mishandle these definitions, but systems with that bug
4149 typically have missing or broken @code{isnan} functions anyway, so it's
4150 probably not worth worrying about.
4154 @prindex @code{malloc}
4155 The C standard says a call @code{malloc (0)} is implementation
4156 dependent. It can return either @code{NULL} or a new non-null pointer.
4157 The latter is more common (e.g., the @acronym{GNU} C Library) but is by
4158 no means universal. @code{AC_FUNC_MALLOC}
4159 can be used to insist on non-@code{NULL} (@pxref{Particular Functions}).
4163 @prindex @code{putenv}
4164 Posix prefers @code{setenv} to @code{putenv}; among other things,
4165 @code{putenv} is not required of all Posix implementations, but
4168 Posix specifies that @code{putenv} puts the given string directly in
4169 @code{environ}, but some systems make a copy of it instead (e.g.,
4170 glibc 2.0, or @acronym{BSD}). And when a copy is made, @code{unsetenv} might
4171 not free it, causing a memory leak (e.g., Free@acronym{BSD} 4).
4173 On some systems @code{putenv ("FOO")} removes @samp{FOO} from the
4174 environment, but this is not standard usage and it dumps core
4175 on some systems (e.g., AIX).
4177 On MinGW, a call @code{putenv ("FOO=")} removes @samp{FOO} from the
4178 environment, rather than inserting it with an empty value.
4180 @item @code{realloc}
4182 @prindex @code{realloc}
4183 The C standard says a call @code{realloc (NULL, size)} is equivalent
4184 to @code{malloc (size)}, but some old systems don't support this (e.g.,
4187 @item @code{signal} handler
4189 @prindex @code{signal}
4190 Normally @code{signal} takes a handler function with a return type of
4191 @code{void}, but some old systems required @code{int} instead. Any
4192 actual @code{int} value returned is not used; this is only a
4193 difference in the function prototype demanded.
4195 All systems we know of in current use return @code{void}. The
4196 @code{int} was to support K&R C, where of course @code{void} is not
4197 available. @code{AC_TYPE_SIGNAL} (@pxref{Particular Types}) can be
4198 used to establish the correct type in all cases.
4200 @item @code{snprintf}
4201 @c @fuindex snprintf
4202 @prindex @code{snprintf}
4203 @c @fuindex vsnprintf
4204 @prindex @code{vsnprintf}
4205 The C99 standard says that if the output array isn't big enough
4206 and if no other errors occur, @code{snprintf} and @code{vsnprintf}
4207 truncate the output and return the number of bytes that ought to have
4208 been produced. Some older systems return the truncated length (e.g.,
4209 @acronym{GNU} C Library 2.0.x or @sc{irix} 6.5), some a negative value
4210 (e.g., earlier @acronym{GNU} C Library versions), and some the buffer
4211 length without truncation (e.g., 32-bit Solaris 7). Also, some buggy
4212 older systems ignore the length and overrun the buffer (e.g., 64-bit
4215 @item @code{sprintf}
4217 @prindex @code{sprintf}
4218 @c @fuindex vsprintf
4219 @prindex @code{vsprintf}
4220 The C standard says @code{sprintf} and @code{vsprintf} return the
4221 number of bytes written. On some ancient systems (SunOS 4 for
4222 instance) they return the buffer pointer instead, but these no
4223 longer need to be worried about.
4227 @prindex @code{sscanf}
4228 On various old systems, e.g., @acronym{HP-UX} 9, @code{sscanf} requires that its
4229 input string be writable (though it doesn't actually change it). This
4230 can be a problem when using @command{gcc} since it normally puts
4231 constant strings in read-only memory (@pxref{Incompatibilities,
4232 Incompatibilities of @acronym{GCC}, , gcc, Using and
4233 Porting the @acronym{GNU} Compiler Collection}). Apparently in some cases even
4234 having format strings read-only can be a problem.
4236 @item @code{strerror_r}
4237 @c @fuindex strerror_r
4238 @prindex @code{strerror_r}
4239 Posix specifies that @code{strerror_r} returns an @code{int}, but many
4240 systems (e.g., @acronym{GNU} C Library version 2.2.4) provide a
4241 different version returning a @code{char *}. @code{AC_FUNC_STRERROR_R}
4242 can detect which is in use (@pxref{Particular Functions}).
4244 @item @code{strnlen}
4246 @prindex @code{strnlen}
4247 @acronym{AIX} 4.3 provides a broken version which produces the
4251 strnlen ("foobar", 0) = 0
4252 strnlen ("foobar", 1) = 3
4253 strnlen ("foobar", 2) = 2
4254 strnlen ("foobar", 3) = 1
4255 strnlen ("foobar", 4) = 0
4256 strnlen ("foobar", 5) = 6
4257 strnlen ("foobar", 6) = 6
4258 strnlen ("foobar", 7) = 6
4259 strnlen ("foobar", 8) = 6
4260 strnlen ("foobar", 9) = 6
4263 @item @code{sysconf}
4265 @prindex @code{sysconf}
4266 @code{_SC_PAGESIZE} is standard, but some older systems (e.g., @acronym{HP-UX}
4267 9) have @code{_SC_PAGE_SIZE} instead. This can be tested with
4272 @prindex @code{unlink}
4273 The Posix spec says that @code{unlink} causes the given file to be
4274 removed only after there are no more open file handles for it. Some
4275 non-Posix hosts have trouble with this requirement, though,
4276 and some @acronym{DOS} variants even corrupt the file system.
4278 @item @code{unsetenv}
4279 @c @fuindex unsetenv
4280 @prindex @code{unsetenv}
4281 On MinGW, @code{unsetenv} is not available, but a variable @samp{FOO}
4282 can be removed with a call @code{putenv ("FOO=")}, as described under
4283 @code{putenv} above.
4285 @item @code{va_copy}
4287 @prindex @code{va_copy}
4288 The C99 standard provides @code{va_copy} for copying
4289 @code{va_list} variables. It may be available in older environments
4290 too, though possibly as @code{__va_copy} (e.g., @command{gcc} in strict
4291 pre-C99 mode). These can be tested with @code{#ifdef}. A fallback to
4292 @code{memcpy (&dst, &src, sizeof (va_list))} gives maximum
4295 @item @code{va_list}
4297 @prindex @code{va_list}
4298 @code{va_list} is not necessarily just a pointer. It can be a
4299 @code{struct} (e.g., @command{gcc} on Alpha), which means @code{NULL} is
4300 not portable. Or it can be an array (e.g., @command{gcc} in some
4301 PowerPC configurations), which means as a function parameter it can be
4302 effectively call-by-reference and library routines might modify the
4303 value back in the caller (e.g., @code{vsnprintf} in the @acronym{GNU} C Library
4306 @item Signed @code{>>}
4307 Normally the C @code{>>} right shift of a signed type replicates the
4308 high bit, giving a so-called ``arithmetic'' shift. But care should be
4309 taken since Standard C doesn't require that behavior. On those
4310 few processors without a native arithmetic shift (for instance Cray
4311 vector systems) zero bits may be shifted in, the same as a shift of an
4314 @item Integer @code{/}
4315 C divides signed integers by truncating their quotient toward zero,
4316 yielding the same result as Fortran. However, before C99 the standard
4317 allowed C implementations to take the floor or ceiling of the quotient
4318 in some cases. Hardly any implementations took advantage of this
4319 freedom, though, and it's probably not worth worrying about this issue
4324 @node Particular Functions
4325 @subsection Particular Function Checks
4326 @cindex Function, checking
4328 These macros check for particular C functions---whether they exist, and
4329 in some cases how they respond when given certain arguments.
4331 @defmac AC_FUNC_ALLOCA
4332 @acindex{FUNC_ALLOCA}
4334 @cvindex HAVE_ALLOCA_H
4337 @prindex @code{alloca}
4339 Check how to get @code{alloca}. Tries to get a builtin version by
4340 checking for @file{alloca.h} or the predefined C preprocessor macros
4341 @code{__GNUC__} and @code{_AIX}. If this macro finds @file{alloca.h},
4342 it defines @code{HAVE_ALLOCA_H}.
4344 If those attempts fail, it looks for the function in the standard C
4345 library. If any of those methods succeed, it defines
4346 @code{HAVE_ALLOCA}. Otherwise, it sets the output variable
4347 @code{ALLOCA} to @samp{$@{LIBOBJDIR@}alloca.o} and defines
4348 @code{C_ALLOCA} (so programs can periodically call @samp{alloca (0)} to
4349 garbage collect). This variable is separate from @code{LIBOBJS} so
4350 multiple programs can share the value of @code{ALLOCA} without needing
4351 to create an actual library, in case only some of them use the code in
4352 @code{LIBOBJS}. The @samp{$@{LIBOBJDIR@}} prefix serves the same
4353 purpose as in @code{LIBOBJS} (@pxref{AC_LIBOBJ vs LIBOBJS}).
4355 This macro does not try to get @code{alloca} from the System V R3
4356 @file{libPW} or the System V R4 @file{libucb} because those libraries
4357 contain some incompatible functions that cause trouble. Some versions
4358 do not even contain @code{alloca} or contain a buggy version. If you
4359 still want to use their @code{alloca}, use @code{ar} to extract
4360 @file{alloca.o} from them instead of compiling @file{alloca.c}.
4362 Source files that use @code{alloca} should start with a piece of code
4363 like the following, to declare it properly.
4367 #ifdef HAVE_ALLOCA_H
4368 # include <alloca.h>
4369 #elif defined __GNUC__
4370 # define alloca __builtin_alloca
4372 # define alloca __alloca
4373 #elif defined _MSC_VER
4374 # include <malloc.h>
4375 # define alloca _alloca
4377 # include <stddef.h>
4381 void *alloca (size_t);
4387 @defmac AC_FUNC_CHOWN
4388 @acindex{FUNC_CHOWN}
4390 @prindex @code{chown}
4391 If the @code{chown} function is available and works (in particular, it
4392 should accept @option{-1} for @code{uid} and @code{gid}), define
4397 @defmac AC_FUNC_CLOSEDIR_VOID
4398 @acindex{FUNC_CLOSEDIR_VOID}
4399 @cvindex CLOSEDIR_VOID
4400 @c @fuindex closedir
4401 @prindex @code{closedir}
4402 If the @code{closedir} function does not return a meaningful value,
4403 define @code{CLOSEDIR_VOID}. Otherwise, callers ought to check its
4404 return value for an error indicator.
4406 Currently this test is implemented by running a test program. When
4407 cross compiling the pessimistic assumption that @code{closedir} does not
4408 return a meaningful value is made.
4410 This macro is obsolescent, as @code{closedir} returns a meaningful value
4411 on current systems. New programs need not use this macro.
4414 @defmac AC_FUNC_ERROR_AT_LINE
4415 @acindex{FUNC_ERROR_AT_LINE}
4416 @c @fuindex error_at_line
4417 @prindex @code{error_at_line}
4418 If the @code{error_at_line} function is not found, require an
4419 @code{AC_LIBOBJ} replacement of @samp{error}.
4422 @defmac AC_FUNC_FNMATCH
4423 @acindex{FUNC_FNMATCH}
4425 @prindex @code{fnmatch}
4426 If the @code{fnmatch} function conforms to Posix, define
4427 @code{HAVE_FNMATCH}. Detect common implementation bugs, for example,
4428 the bugs in Solaris 2.4.
4430 Unlike the other specific
4431 @code{AC_FUNC} macros, @code{AC_FUNC_FNMATCH} does not replace a
4432 broken/missing @code{fnmatch}. This is for historical reasons.
4433 See @code{AC_REPLACE_FNMATCH} below.
4435 This macro is obsolescent. New programs should use Gnulib's
4436 @code{fnmatch-posix} module. @xref{Gnulib}.
4439 @defmac AC_FUNC_FNMATCH_GNU
4440 @acindex{FUNC_FNMATCH_GNU}
4442 @prindex @code{fnmatch}
4443 Behave like @code{AC_REPLACE_FNMATCH} (@emph{replace}) but also test
4444 whether @code{fnmatch} supports @acronym{GNU} extensions. Detect common
4445 implementation bugs, for example, the bugs in the @acronym{GNU} C
4448 This macro is obsolescent. New programs should use Gnulib's
4449 @code{fnmatch-gnu} module. @xref{Gnulib}.
4452 @defmac AC_FUNC_FORK
4454 @cvindex HAVE_VFORK_H
4455 @cvindex HAVE_WORKING_FORK
4456 @cvindex HAVE_WORKING_VFORK
4459 @prindex @code{fork}
4461 @prindex @code{vfork}
4463 This macro checks for the @code{fork} and @code{vfork} functions. If a
4464 working @code{fork} is found, define @code{HAVE_WORKING_FORK}. This macro
4465 checks whether @code{fork} is just a stub by trying to run it.
4467 If @file{vfork.h} is found, define @code{HAVE_VFORK_H}. If a working
4468 @code{vfork} is found, define @code{HAVE_WORKING_VFORK}. Otherwise,
4469 define @code{vfork} to be @code{fork} for backward compatibility with
4470 previous versions of @command{autoconf}. This macro checks for several known
4471 errors in implementations of @code{vfork} and considers the system to not
4472 have a working @code{vfork} if it detects any of them. It is not considered
4473 to be an implementation error if a child's invocation of @code{signal}
4474 modifies the parent's signal handler, since child processes rarely change
4475 their signal handlers.
4477 Since this macro defines @code{vfork} only for backward compatibility with
4478 previous versions of @command{autoconf} you're encouraged to define it
4479 yourself in new code:
4482 #ifndef HAVE_WORKING_VFORK
4489 @defmac AC_FUNC_FSEEKO
4490 @acindex{FUNC_FSEEKO}
4491 @cvindex _LARGEFILE_SOURCE
4493 @prindex @code{fseeko}
4494 If the @code{fseeko} function is available, define @code{HAVE_FSEEKO}.
4495 Define @code{_LARGEFILE_SOURCE} if necessary to make the prototype
4496 visible on some systems (e.g., glibc 2.2). Otherwise linkage problems
4497 may occur when compiling with @code{AC_SYS_LARGEFILE} on
4498 largefile-sensitive systems where @code{off_t} does not default to a
4502 @defmac AC_FUNC_GETGROUPS
4503 @acindex{FUNC_GETGROUPS}
4504 @ovindex GETGROUPS_LIBS
4505 @c @fuindex getgroups
4506 @prindex @code{getgroups}
4507 If the @code{getgroups} function is available and works (unlike on
4508 Ultrix 4.3, where @samp{getgroups (0, 0)} always fails), define
4509 @code{HAVE_GETGROUPS}. Set @code{GETGROUPS_LIBS} to any libraries
4510 needed to get that function. This macro runs @code{AC_TYPE_GETGROUPS}.
4513 @defmac AC_FUNC_GETLOADAVG
4514 @acindex{FUNC_GETLOADAVG}
4519 @cvindex HAVE_NLIST_H
4520 @cvindex NLIST_NAME_UNION
4521 @cvindex GETLOADAVG_PRIVILEGED
4522 @cvindex NEED_SETGID
4523 @cvindex C_GETLOADAVG
4525 @ovindex NEED_SETGID
4527 @ovindex GETLOADAVG_LIBS
4528 @c @fuindex getloadavg
4529 @prindex @code{getloadavg}
4530 Check how to get the system load averages. To perform its tests
4531 properly, this macro needs the file @file{getloadavg.c}; therefore, be
4532 sure to set the @code{AC_LIBOBJ} replacement directory properly (see
4533 @ref{Generic Functions}, @code{AC_CONFIG_LIBOBJ_DIR}).
4535 If the system has the @code{getloadavg} function, define
4536 @code{HAVE_GETLOADAVG}, and set @code{GETLOADAVG_LIBS} to any libraries
4537 necessary to get that function. Also add @code{GETLOADAVG_LIBS} to
4538 @code{LIBS}. Otherwise, require an @code{AC_LIBOBJ} replacement for
4539 @samp{getloadavg} with source code in @file{@var{dir}/getloadavg.c}, and
4540 possibly define several other C preprocessor macros and output
4545 Define @code{C_GETLOADAVG}.
4548 Define @code{SVR4}, @code{DGUX}, @code{UMAX}, or @code{UMAX4_3} if on
4553 If @file{nlist.h} is found, define @code{HAVE_NLIST_H}.
4556 If @samp{struct nlist} has an @samp{n_un.n_name} member, define
4557 @code{HAVE_STRUCT_NLIST_N_UN_N_NAME}. The obsolete symbol
4558 @code{NLIST_NAME_UNION} is still defined, but do not depend upon it.
4561 Programs may need to be installed set-group-ID (or set-user-ID) for
4562 @code{getloadavg} to work. In this case, define
4563 @code{GETLOADAVG_PRIVILEGED}, set the output variable @code{NEED_SETGID}
4564 to @samp{true} (and otherwise to @samp{false}), and set
4565 @code{KMEM_GROUP} to the name of the group that should own the installed
4569 The @code{AC_FUNC_GETLOADAVG} macro is obsolescent. New programs should
4570 use Gnulib's @code{getloadavg} module. @xref{Gnulib}.
4573 @defmac AC_FUNC_GETMNTENT
4574 @acindex{FUNC_GETMNTENT}
4575 @cvindex HAVE_GETMNTENT
4576 @c @fuindex getmntent
4577 @prindex @code{getmntent}
4578 Check for @code{getmntent} in the standard C library, and then in the
4579 @file{sun}, @file{seq}, and @file{gen} libraries, for @sc{unicos},
4580 @sc{irix} 4, @sc{ptx}, and UnixWare, respectively. Then, if
4581 @code{getmntent} is available, define @code{HAVE_GETMNTENT}.
4584 @defmac AC_FUNC_GETPGRP
4585 @acindex{FUNC_GETPGRP}
4586 @cvindex GETPGRP_VOID
4589 @prindex @code{getpgid}
4590 @prindex @code{getpgrp}
4591 Define @code{GETPGRP_VOID} if it is an error to pass 0 to
4592 @code{getpgrp}; this is the Posix behavior. On older @acronym{BSD}
4593 systems, you must pass 0 to @code{getpgrp}, as it takes an argument and
4594 behaves like Posix's @code{getpgid}.
4604 This macro does not check whether
4605 @code{getpgrp} exists at all; if you need to work in that situation,
4606 first call @code{AC_CHECK_FUNC} for @code{getpgrp}.
4608 This macro is obsolescent, as current systems have a @code{getpgrp}
4609 whose signature conforms to Posix. New programs need not use this macro.
4612 @defmac AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK
4613 @acindex{FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK}
4614 @cvindex LSTAT_FOLLOWS_SLASHED_SYMLINK
4616 @prindex @code{lstat}
4617 If @file{link} is a symbolic link, then @code{lstat} should treat
4618 @file{link/} the same as @file{link/.}. However, many older
4619 @code{lstat} implementations incorrectly ignore trailing slashes.
4621 It is safe to assume that if @code{lstat} incorrectly ignores
4622 trailing slashes, then other symbolic-link-aware functions like
4623 @code{unlink} also incorrectly ignore trailing slashes.
4625 If @code{lstat} behaves properly, define
4626 @code{LSTAT_FOLLOWS_SLASHED_SYMLINK}, otherwise require an
4627 @code{AC_LIBOBJ} replacement of @code{lstat}.
4630 @defmac AC_FUNC_MALLOC
4631 @acindex{FUNC_MALLOC}
4632 @cvindex HAVE_MALLOC
4635 @prindex @code{malloc}
4636 If the @code{malloc} function is compatible with the @acronym{GNU} C
4637 library @code{malloc} (i.e., @samp{malloc (0)} returns a valid
4638 pointer), define @code{HAVE_MALLOC} to 1. Otherwise define
4639 @code{HAVE_MALLOC} to 0, ask for an @code{AC_LIBOBJ} replacement for
4640 @samp{malloc}, and define @code{malloc} to @code{rpl_malloc} so that the
4641 native @code{malloc} is not used in the main project.
4643 Typically, the replacement file @file{malloc.c} should look like (note
4644 the @samp{#undef malloc}):
4647 #ifdef HAVE_CONFIG_H
4648 # include <config.h>
4652 #include <sys/types.h>
4656 /* Allocate an N-byte block of memory from the heap.
4657 If N is zero, allocate a 1-byte block. */
4660 rpl_malloc (size_t n)
4669 @defmac AC_FUNC_MEMCMP
4670 @acindex{FUNC_MEMCMP}
4673 @prindex @code{memcmp}
4674 If the @code{memcmp} function is not available, or does not work on
4675 8-bit data (like the one on SunOS 4.1.3), or fails when comparing 16
4676 bytes or more and with at least one buffer not starting on a 4-byte
4677 boundary (such as the one on NeXT x86 OpenStep), require an
4678 @code{AC_LIBOBJ} replacement for @samp{memcmp}.
4680 This macro is obsolescent, as current systems have a working
4681 @code{memcmp}. New programs need not use this macro.
4684 @defmac AC_FUNC_MBRTOWC
4685 @acindex{FUNC_MBRTOWC}
4686 @cvindex HAVE_MBRTOWC
4688 @prindex @code{mbrtowc}
4689 Define @code{HAVE_MBRTOWC} to 1 if the function @code{mbrtowc} and the
4690 type @code{mbstate_t} are properly declared.
4693 @defmac AC_FUNC_MKTIME
4694 @acindex{FUNC_MKTIME}
4697 @prindex @code{mktime}
4698 If the @code{mktime} function is not available, or does not work
4699 correctly, require an @code{AC_LIBOBJ} replacement for @samp{mktime}.
4700 For the purposes of this test, @code{mktime} should conform to the
4701 Posix standard and should be the inverse of
4705 @defmac AC_FUNC_MMAP
4709 @prindex @code{mmap}
4710 If the @code{mmap} function exists and works correctly, define
4711 @code{HAVE_MMAP}. This checks only private fixed mapping of already-mapped
4715 @defmac AC_FUNC_OBSTACK
4716 @acindex{FUNC_OBSTACK}
4717 @cvindex HAVE_OBSTACK
4719 If the obstacks are found, define @code{HAVE_OBSTACK}, else require an
4720 @code{AC_LIBOBJ} replacement for @samp{obstack}.
4723 @defmac AC_FUNC_REALLOC
4724 @acindex{FUNC_REALLOC}
4725 @cvindex HAVE_REALLOC
4728 @prindex @code{realloc}
4729 If the @code{realloc} function is compatible with the @acronym{GNU} C
4730 library @code{realloc} (i.e., @samp{realloc (NULL, 0)} returns a
4731 valid pointer), define @code{HAVE_REALLOC} to 1. Otherwise define
4732 @code{HAVE_REALLOC} to 0, ask for an @code{AC_LIBOBJ} replacement for
4733 @samp{realloc}, and define @code{realloc} to @code{rpl_realloc} so that
4734 the native @code{realloc} is not used in the main project. See
4735 @code{AC_FUNC_MALLOC} for details.
4738 @defmac AC_FUNC_SELECT_ARGTYPES
4739 @acindex{FUNC_SELECT_ARGTYPES}
4740 @cvindex SELECT_TYPE_ARG1
4741 @cvindex SELECT_TYPE_ARG234
4742 @cvindex SELECT_TYPE_ARG5
4744 @prindex @code{select}
4745 Determines the correct type to be passed for each of the
4746 @code{select} function's arguments, and defines those types
4747 in @code{SELECT_TYPE_ARG1}, @code{SELECT_TYPE_ARG234}, and
4748 @code{SELECT_TYPE_ARG5} respectively. @code{SELECT_TYPE_ARG1} defaults
4749 to @samp{int}, @code{SELECT_TYPE_ARG234} defaults to @samp{int *},
4750 and @code{SELECT_TYPE_ARG5} defaults to @samp{struct timeval *}.
4752 This macro is obsolescent, as current systems have a @code{select} whose
4753 signature conforms to Posix. New programs need not use this macro.
4756 @defmac AC_FUNC_SETPGRP
4757 @acindex{FUNC_SETPGRP}
4758 @cvindex SETPGRP_VOID
4760 @prindex @code{setpgrp}
4761 If @code{setpgrp} takes no argument (the Posix version), define
4762 @code{SETPGRP_VOID}. Otherwise, it is the @acronym{BSD} version, which takes
4763 two process IDs as arguments. This macro does not check whether
4764 @code{setpgrp} exists at all; if you need to work in that situation,
4765 first call @code{AC_CHECK_FUNC} for @code{setpgrp}.
4767 This macro is obsolescent, as current systems have a @code{setpgrp}
4768 whose signature conforms to Posix. New programs need not use this macro.
4771 @defmac AC_FUNC_STAT
4772 @defmacx AC_FUNC_LSTAT
4774 @acindex{FUNC_LSTAT}
4775 @cvindex HAVE_STAT_EMPTY_STRING_BUG
4776 @cvindex HAVE_LSTAT_EMPTY_STRING_BUG
4778 @prindex @code{stat}
4780 @prindex @code{lstat}
4781 Determine whether @code{stat} or @code{lstat} have the bug that it
4782 succeeds when given the zero-length file name as argument. The @code{stat}
4783 and @code{lstat} from SunOS 4.1.4 and the Hurd (as of 1998-11-01) do
4786 If it does, then define @code{HAVE_STAT_EMPTY_STRING_BUG} (or
4787 @code{HAVE_LSTAT_EMPTY_STRING_BUG}) and ask for an @code{AC_LIBOBJ}
4790 These macros are obsolescent, as no current systems have the bug.
4791 New programs need not use these macros.
4794 @defmac AC_FUNC_STRCOLL
4795 @acindex{FUNC_STRCOLL}
4796 @cvindex HAVE_STRCOLL
4798 @prindex @code{strcoll}
4799 If the @code{strcoll} function exists and works correctly, define
4800 @code{HAVE_STRCOLL}. This does a bit more than
4801 @samp{AC_CHECK_FUNCS(strcoll)}, because some systems have incorrect
4802 definitions of @code{strcoll} that should not be used.
4805 @defmac AC_FUNC_STRERROR_R
4806 @acindex{FUNC_STRERROR_R}
4807 @cvindex HAVE_STRERROR_R
4808 @cvindex HAVE_DECL_STRERROR_R
4809 @cvindex STRERROR_R_CHAR_P
4810 @c @fuindex strerror_r
4811 @prindex @code{strerror_r}
4812 If @code{strerror_r} is available, define @code{HAVE_STRERROR_R}, and if
4813 it is declared, define @code{HAVE_DECL_STRERROR_R}. If it returns a
4814 @code{char *} message, define @code{STRERROR_R_CHAR_P}; otherwise it
4815 returns an @code{int} error number. The Thread-Safe Functions option of
4816 Posix requires @code{strerror_r} to return @code{int}, but
4817 many systems (including, for example, version 2.2.4 of the @acronym{GNU} C
4818 Library) return a @code{char *} value that is not necessarily equal to
4819 the buffer argument.
4822 @defmac AC_FUNC_STRFTIME
4823 @acindex{FUNC_STRFTIME}
4824 @cvindex HAVE_STRFTIME
4825 @c @fuindex strftime
4826 @prindex @code{strftime}
4827 Check for @code{strftime} in the @file{intl} library, for SCO Unix.
4828 Then, if @code{strftime} is available, define @code{HAVE_STRFTIME}.
4830 This macro is obsolescent, as no current systems require the @file{intl}
4831 library for @code{strftime}. New programs need not use this macro.
4834 @defmac AC_FUNC_STRTOD
4835 @acindex{FUNC_STRTOD}
4838 @prindex @code{strtod}
4839 If the @code{strtod} function does not exist or doesn't work correctly,
4840 ask for an @code{AC_LIBOBJ} replacement of @samp{strtod}. In this case,
4841 because @file{strtod.c} is likely to need @samp{pow}, set the output
4842 variable @code{POW_LIB} to the extra library needed.
4845 @defmac AC_FUNC_STRTOLD
4846 @acindex{FUNC_STRTOLD}
4847 @prindex @code{strtold}
4848 If the @code{strtold} function exists and conforms to C99, define
4849 @code{HAVE_STRTOLD}.
4852 @defmac AC_FUNC_STRNLEN
4853 @acindex{FUNC_STRNLEN}
4854 @cvindex HAVE_STRNLEN
4856 @prindex @code{strnlen}
4857 If the @code{strnlen} function is not available, or is buggy (like the one
4858 from @acronym{AIX} 4.3), require an @code{AC_LIBOBJ} replacement for it.
4861 @defmac AC_FUNC_UTIME_NULL
4862 @acindex{FUNC_UTIME_NULL}
4863 @cvindex HAVE_UTIME_NULL
4865 @prindex @code{utime}
4866 If @samp{utime (@var{file}, NULL)} sets @var{file}'s timestamp to
4867 the present, define @code{HAVE_UTIME_NULL}.
4869 This macro is obsolescent, as all current systems have a @code{utime}
4870 that behaves this way. New programs need not use this macro.
4873 @defmac AC_FUNC_VPRINTF
4874 @acindex{FUNC_VPRINTF}
4875 @cvindex HAVE_VPRINTF
4876 @cvindex HAVE_DOPRNT
4878 @prindex @code{vprintf}
4879 If @code{vprintf} is found, define @code{HAVE_VPRINTF}. Otherwise, if
4880 @code{_doprnt} is found, define @code{HAVE_DOPRNT}. (If @code{vprintf}
4881 is available, you may assume that @code{vfprintf} and @code{vsprintf}
4882 are also available.)
4884 This macro is obsolescent, as all current systems have @code{vprintf}.
4885 New programs need not use this macro.
4888 @defmac AC_REPLACE_FNMATCH
4889 @acindex{REPLACE_FNMATCH}
4891 @prindex @code{fnmatch}
4892 @hdrindex{fnmatch.h}
4893 If the @code{fnmatch} function does not conform to Posix (see
4894 @code{AC_FUNC_FNMATCH}), ask for its @code{AC_LIBOBJ} replacement.
4896 The files @file{fnmatch.c}, @file{fnmatch_loop.c}, and @file{fnmatch_.h}
4897 in the @code{AC_LIBOBJ} replacement directory are assumed to contain a
4898 copy of the source code of @acronym{GNU} @code{fnmatch}. If necessary,
4899 this source code is compiled as an @code{AC_LIBOBJ} replacement, and the
4900 @file{fnmatch_.h} file is linked to @file{fnmatch.h} so that it can be
4901 included in place of the system @code{<fnmatch.h>}.
4903 This macro is obsolescent, as it assumes the use of particular source
4904 files. New programs should use Gnulib's @code{fnmatch-posix} module,
4905 which provides this macro along with the source files. @xref{Gnulib}.
4910 @node Generic Functions
4911 @subsection Generic Function Checks
4913 These macros are used to find functions not covered by the ``particular''
4914 test macros. If the functions might be in libraries other than the
4915 default C library, first call @code{AC_CHECK_LIB} for those libraries.
4916 If you need to check the behavior of a function as well as find out
4917 whether it is present, you have to write your own test for
4918 it (@pxref{Writing Tests}).
4920 @defmac AC_CHECK_FUNC (@var{function}, @ovar{action-if-found}, @ovar{action-if-not-found})
4921 @acindex{CHECK_FUNC}
4922 If C function @var{function} is available, run shell commands
4923 @var{action-if-found}, otherwise @var{action-if-not-found}. If you just
4924 want to define a symbol if the function is available, consider using
4925 @code{AC_CHECK_FUNCS} instead. This macro checks for functions with C
4926 linkage even when @code{AC_LANG(C++)} has been called, since C is more
4927 standardized than C++. (@pxref{Language Choice}, for more information
4928 about selecting the language for checks.)
4931 @defmac AC_CHECK_FUNCS (@var{function}@dots{}, @ovar{action-if-found}, @ovar{action-if-not-found})
4932 @acindex{CHECK_FUNCS}
4933 @cvindex HAVE_@var{function}
4934 For each @var{function} enumerated in the blank-or-newline-separated argument
4935 list, define @code{HAVE_@var{function}} (in all capitals) if it is available.
4936 If @var{action-if-found} is given, it is additional shell code to
4937 execute when one of the functions is found. You can give it a value of
4938 @samp{break} to break out of the loop on the first match. If
4939 @var{action-if-not-found} is given, it is executed when one of the
4940 functions is not found.
4943 @defmac AC_CHECK_FUNCS_ONCE (@var{function}@dots{})
4944 @acindex{CHECK_FUNCS_ONCE}
4945 @cvindex HAVE_@var{function}
4946 For each @var{function} enumerated in the blank-or-newline-separated argument
4947 list, define @code{HAVE_@var{function}} (in all capitals) if it is available.
4948 This is a once-only variant of @code{AC_CHECK_FUNCS}. It generates the
4949 checking code at most once, so that @command{configure} is smaller and
4950 faster; but the checks cannot be conditionalized and are always done once,
4951 early during the @command{configure} run.
4956 Autoconf follows a philosophy that was formed over the years by those
4957 who have struggled for portability: isolate the portability issues in
4958 specific files, and then program as if you were in a Posix
4959 environment. Some functions may be missing or unfixable, and your
4960 package must be ready to replace them.
4962 Suitable replacements for many such problem functions are available from
4963 Gnulib (@pxref{Gnulib}).
4965 @defmac AC_LIBOBJ (@var{function})
4968 Specify that @samp{@var{function}.c} must be included in the executables
4969 to replace a missing or broken implementation of @var{function}.
4971 Technically, it adds @samp{@var{function}.$ac_objext} to the output
4972 variable @code{LIBOBJS} if it is not already in, and calls
4973 @code{AC_LIBSOURCE} for @samp{@var{function}.c}. You should not
4974 directly change @code{LIBOBJS}, since this is not traceable.
4977 @defmac AC_LIBSOURCE (@var{file})
4979 Specify that @var{file} might be needed to compile the project. If you
4980 need to know what files might be needed by a @file{configure.ac}, you
4981 should trace @code{AC_LIBSOURCE}. @var{file} must be a literal.
4983 This macro is called automatically from @code{AC_LIBOBJ}, but you must
4984 call it explicitly if you pass a shell variable to @code{AC_LIBOBJ}. In
4985 that case, since shell variables cannot be traced statically, you must
4986 pass to @code{AC_LIBSOURCE} any possible files that the shell variable
4987 might cause @code{AC_LIBOBJ} to need. For example, if you want to pass
4988 a variable @code{$foo_or_bar} to @code{AC_LIBOBJ} that holds either
4989 @code{"foo"} or @code{"bar"}, you should do:
4992 AC_LIBSOURCE([foo.c])
4993 AC_LIBSOURCE([bar.c])
4994 AC_LIBOBJ([$foo_or_bar])
4998 There is usually a way to avoid this, however, and you are encouraged to
4999 simply call @code{AC_LIBOBJ} with literal arguments.
5001 Note that this macro replaces the obsolete @code{AC_LIBOBJ_DECL}, with
5002 slightly different semantics: the old macro took the function name,
5003 e.g., @code{foo}, as its argument rather than the file name.
5006 @defmac AC_LIBSOURCES (@var{files})
5007 @acindex{LIBSOURCES}
5008 Like @code{AC_LIBSOURCE}, but accepts one or more @var{files} in a
5009 comma-separated M4 list. Thus, the above example might be rewritten:
5012 AC_LIBSOURCES([foo.c, bar.c])
5013 AC_LIBOBJ([$foo_or_bar])
5017 @defmac AC_CONFIG_LIBOBJ_DIR (@var{directory})
5018 @acindex{CONFIG_LIBOBJ_DIR}
5019 Specify that @code{AC_LIBOBJ} replacement files are to be found in
5020 @var{directory}, a name relative to the top level of the
5021 source tree. The replacement directory defaults to @file{.}, the top
5022 level directory, and the most typical value is @file{lib}, corresponding
5023 to @samp{AC_CONFIG_LIBOBJ_DIR([lib])}.
5025 @command{configure} might need to know the replacement directory for the
5026 following reasons: (i) some checks use the replacement files, (ii) some
5027 macros bypass broken system headers by installing links to the
5028 replacement headers (iii) when used in conjunction with Automake,
5029 within each makefile, @var{directory} is used as a relative path
5030 from @code{$(top_srcdir)} to each object named in @code{LIBOBJS} and
5031 @code{LTLIBOBJS}, etc.
5036 It is common to merely check for the existence of a function, and ask
5037 for its @code{AC_LIBOBJ} replacement if missing. The following macro is
5038 a convenient shorthand.
5040 @defmac AC_REPLACE_FUNCS (@var{function}@dots{})
5041 @acindex{REPLACE_FUNCS}
5043 Like @code{AC_CHECK_FUNCS}, but uses @samp{AC_LIBOBJ(@var{function})} as
5044 @var{action-if-not-found}. You can declare your replacement function by
5045 enclosing the prototype in @samp{#ifndef HAVE_@var{function}}. If the
5046 system has the function, it probably declares it in a header file you
5047 should be including, so you shouldn't redeclare it lest your declaration
5052 @section Header Files
5053 @cindex Header, checking
5055 The following macros check for the presence of certain C header files.
5056 If there is no macro specifically defined to check for a header file you need,
5057 and you don't need to check for any special properties of
5058 it, then you can use one of the general header-file check macros.
5061 * Header Portability:: Collected knowledge on common headers
5062 * Particular Headers:: Special handling to find certain headers
5063 * Generic Headers:: How to find other headers
5066 @node Header Portability
5067 @subsection Portability of Headers
5068 @cindex Portability of headers
5069 @cindex Header portability
5071 This section tries to collect knowledge about common headers, and the
5072 problems they cause. By definition, this list always requires
5073 additions. Please help us keeping it as complete as possible.
5077 @item @file{limits.h}
5078 C99 says that @file{limits.h} defines @code{LLONG_MIN},
5079 @code{LLONG_MAX}, and @code{ULLONG_MAX}, but many almost-C99
5080 environments (e.g., default @acronym{GCC} 4.0.2 + glibc 2.4) do not
5083 @item @file{inttypes.h} vs.@: @file{stdint.h}
5084 @hdrindex{inttypes.h}
5086 The C99 standard says that @file{inttypes.h} includes
5087 @file{stdint.h}, so there's no need to include @file{stdint.h}
5088 separately in a standard environment. Some implementations have
5089 @file{inttypes.h} but not @file{stdint.h} (e.g., Solaris 7), but we don't
5090 know of any implementation that has @file{stdint.h} but not
5093 @item @file{linux/irda.h}
5094 @hdrindex{linux/irda.h}
5095 It requires @file{linux/types.h} and @file{sys/socket.h}.
5097 @item @file{linux/random.h}
5098 @hdrindex{linux/random.h}
5099 It requires @file{linux/types.h}.
5101 @item @file{net/if.h}
5103 On Darwin, this file requires that @file{sys/socket.h} be included
5104 beforehand. One should run:
5107 AC_CHECK_HEADERS([sys/socket.h])
5108 AC_CHECK_HEADERS([net/if.h], [], [],
5111 # include <stdlib.h>
5112 # include <stddef.h>
5114 # ifdef HAVE_STDLIB_H
5115 # include <stdlib.h>
5118 #ifdef HAVE_SYS_SOCKET_H
5119 # include <sys/socket.h>
5124 @item @file{netinet/if_ether.h}
5125 @hdrindex{netinet/if_ether.h}
5126 On Darwin, this file requires that @file{stdio.h} and
5127 @file{sys/socket.h} be included beforehand. One should run:
5130 AC_CHECK_HEADERS([sys/socket.h])
5131 AC_CHECK_HEADERS([netinet/if_ether.h], [], [],
5134 # include <stdlib.h>
5135 # include <stddef.h>
5137 # ifdef HAVE_STDLIB_H
5138 # include <stdlib.h>
5141 #ifdef HAVE_SYS_SOCKET_H
5142 # include <sys/socket.h>
5147 @item @file{stdint.h}
5148 See above, item @file{inttypes.h} vs.@: @file{stdint.h}.
5150 @item @file{stdlib.h}
5152 On many systems (e.g., Darwin), @file{stdio.h} is a prerequisite.
5154 @item @file{sys/mount.h}
5155 @hdrindex{sys/mount.h}
5156 On Free@acronym{BSD} 4.8 on ia32 and using gcc version 2.95.4,
5157 @file{sys/params.h} is a prerequisite.
5159 @item @file{sys/ptem.h}
5160 @hdrindex{sys/ptem.h}
5161 On Solaris 8, @file{sys/stream.h} is a prerequisite.
5163 @item @file{sys/socket.h}
5164 @hdrindex{sys/socket.h}
5165 On Darwin, @file{stdlib.h} is a prerequisite.
5167 @item @file{sys/ucred.h}
5168 @hdrindex{sys/ucred.h}
5169 On Tru64 5.1, @file{sys/types.h} is a prerequisite.
5171 @item @file{X11/extensions/scrnsaver.h}
5172 @hdrindex{X11/extensions/scrnsaver.h}
5173 Using XFree86, this header requires @file{X11/Xlib.h}, which is probably
5174 so required that you might not even consider looking for it.
5177 AC_CHECK_HEADERS([X11/extensions/scrnsaver.h], [], [],
5178 [[#include <X11/Xlib.h>
5184 @node Particular Headers
5185 @subsection Particular Header Checks
5187 These macros check for particular system header files---whether they
5188 exist, and in some cases whether they declare certain symbols.
5190 @defmac AC_HEADER_ASSERT
5191 @acindex{HEADER_ASSERT}
5194 Check whether to enable assertions in the style of @file{assert.h}.
5195 Assertions are enabled by default, but the user can override this by
5196 invoking @command{configure} with the @option{--disable-assert} option.
5199 @defmac AC_HEADER_DIRENT
5200 @acindex{HEADER_DIRENT}
5201 @cvindex HAVE_DIRENT_H
5202 @cvindex HAVE_NDIR_H
5203 @cvindex HAVE_SYS_DIR_H
5204 @cvindex HAVE_SYS_NDIR_H
5206 @hdrindex{sys/ndir.h}
5207 @hdrindex{sys/dir.h}
5209 Check for the following header files. For the first one that is
5210 found and defines @samp{DIR}, define the listed C preprocessor macro:
5212 @multitable {@file{sys/ndir.h}} {@code{HAVE_SYS_NDIR_H}}
5213 @item @file{dirent.h} @tab @code{HAVE_DIRENT_H}
5214 @item @file{sys/ndir.h} @tab @code{HAVE_SYS_NDIR_H}
5215 @item @file{sys/dir.h} @tab @code{HAVE_SYS_DIR_H}
5216 @item @file{ndir.h} @tab @code{HAVE_NDIR_H}
5219 The directory-library declarations in your source code should look
5220 something like the following:
5224 #include <sys/types.h>
5225 #ifdef HAVE_DIRENT_H
5226 # include <dirent.h>
5227 # define NAMLEN(dirent) strlen ((dirent)->d_name)
5229 # define dirent direct
5230 # define NAMLEN(dirent) ((dirent)->d_namlen)
5231 # ifdef HAVE_SYS_NDIR_H
5232 # include <sys/ndir.h>
5234 # ifdef HAVE_SYS_DIR_H
5235 # include <sys/dir.h>
5244 Using the above declarations, the program would declare variables to be
5245 of type @code{struct dirent}, not @code{struct direct}, and would access
5246 the length of a directory entry name by passing a pointer to a
5247 @code{struct dirent} to the @code{NAMLEN} macro.
5249 This macro also checks for the SCO Xenix @file{dir} and @file{x} libraries.
5251 This macro is obsolescent, as all current systems with directory
5252 libraries have @code{<dirent.h>}. New programs need not use this macro.
5254 Also see @code{AC_STRUCT_DIRENT_D_INO} and
5255 @code{AC_STRUCT_DIRENT_D_TYPE} (@pxref{Particular Structures}).
5258 @defmac AC_HEADER_MAJOR
5259 @acindex{HEADER_MAJOR}
5260 @cvindex MAJOR_IN_MKDEV
5261 @cvindex MAJOR_IN_SYSMACROS
5262 @hdrindex{sys/mkdev.h}
5263 @hdrindex{sys/sysmacros.h}
5264 If @file{sys/types.h} does not define @code{major}, @code{minor}, and
5265 @code{makedev}, but @file{sys/mkdev.h} does, define
5266 @code{MAJOR_IN_MKDEV}; otherwise, if @file{sys/sysmacros.h} does, define
5267 @code{MAJOR_IN_SYSMACROS}.
5270 @defmac AC_HEADER_RESOLV
5271 @acindex{HEADER_RESOLV}
5272 @cvindex HAVE_RESOLV_H
5274 Checks for header @file{resolv.h}, checking for prerequisites first.
5275 To properly use @file{resolv.h}, your code should contain something like
5279 #ifdef HAVE_SYS_TYPES_H
5280 # include <sys/types.h>
5282 #ifdef HAVE_NETINET_IN_H
5283 # include <netinet/in.h> /* inet_ functions / structs */
5285 #ifdef HAVE_ARPA_NAMESER_H
5286 # include <arpa/nameser.h> /* DNS HEADER struct */
5295 @defmac AC_HEADER_STAT
5296 @acindex{HEADER_STAT}
5297 @cvindex STAT_MACROS_BROKEN
5298 @hdrindex{sys/stat.h}
5299 If the macros @code{S_ISDIR}, @code{S_ISREG}, etc.@: defined in
5300 @file{sys/stat.h} do not work properly (returning false positives),
5301 define @code{STAT_MACROS_BROKEN}. This is the case on Tektronix UTekV,
5302 Amdahl UTS and Motorola System V/88.
5304 This macro is obsolescent, as no current systems have the bug.
5305 New programs need not use this macro.
5308 @defmac AC_HEADER_STDBOOL
5309 @acindex{HEADER_STDBOOL}
5310 @cvindex HAVE_STDBOOL_H
5312 @hdrindex{stdbool.h}
5314 If @file{stdbool.h} exists and conforms to C99, define
5315 @code{HAVE_STDBOOL_H} to 1; if the type @code{_Bool} is defined, define
5316 @code{HAVE__BOOL} to 1. To fulfill the C99 requirements, your
5317 @file{system.h} could contain the following code:
5320 #ifdef HAVE_STDBOOL_H
5321 # include <stdbool.h>
5327 # define _Bool signed char
5333 # define __bool_true_false_are_defined 1
5337 Alternatively you can use the @samp{stdbool} package of Gnulib
5338 (@pxref{Gnulib}); it packages the above code into a replacement header
5339 and contains a few other bells and whistles.
5344 @defmac AC_HEADER_STDC
5345 @acindex{HEADER_STDC}
5346 @cvindex STDC_HEADERS
5352 Define @code{STDC_HEADERS} if the system has C header files
5353 conforming to @acronym{ANSI} C89 (@acronym{ISO} C90).
5354 Specifically, this macro checks for @file{stdlib.h}, @file{stdarg.h},
5355 @file{string.h}, and @file{float.h}; if the system has those, it
5356 probably has the rest of the C89 header files. This macro also
5357 checks whether @file{string.h} declares @code{memchr} (and thus
5358 presumably the other @code{mem} functions), whether @file{stdlib.h}
5359 declare @code{free} (and thus presumably @code{malloc} and other related
5360 functions), and whether the @file{ctype.h} macros work on characters
5361 with the high bit set, as the C standard requires.
5363 If you use this macro, your code can refer to @code{STDC_HEADERS} to
5364 determine whether the system has conforming header files (and probably C
5367 This macro is obsolescent, as current systems have conforming header
5368 files. New programs need not use this macro.
5371 @hdrindex{strings.h}
5372 Nowadays @file{string.h} is part of the C standard and declares functions like
5373 @code{strcpy}, and @file{strings.h} is standardized by Posix and declares
5374 @acronym{BSD} functions like @code{bcopy}; but
5375 historically, string functions were a major sticking point in this area.
5376 If you still want to worry about portability to ancient systems without
5377 standard headers, there is so much variation
5378 that it is probably easier to declare the functions you use than to
5379 figure out exactly what the system header files declare. Some ancient systems
5380 contained a mix of functions from the C standard and from @acronym{BSD};
5381 some were mostly standard but lacked @samp{memmove}; some defined the
5382 @acronym{BSD} functions as macros in @file{string.h} or
5383 @file{strings.h}; some had only the @acronym{BSD} functions but
5384 @file{string.h}; some declared the memory functions in @file{memory.h},
5385 some in @file{string.h}; etc. It is probably sufficient to check for
5386 one string function and one memory function; if the library had the
5387 standard versions of those then it probably had most of the others.
5388 If you put the following in @file{configure.ac}:
5391 # This example is obsolescent.
5392 # Nowadays you can omit these macro calls.
5394 AC_CHECK_FUNCS([strchr memcpy])
5398 then, in your code, you can use declarations like this:
5402 /* This example is obsolescent.
5403 Nowadays you can just #include <string.h>. */
5405 # include <string.h>
5407 # ifndef HAVE_STRCHR
5408 # define strchr index
5409 # define strrchr rindex
5411 char *strchr (), *strrchr ();
5412 # ifndef HAVE_MEMCPY
5413 # define memcpy(d, s, n) bcopy ((s), (d), (n))
5414 # define memmove(d, s, n) bcopy ((s), (d), (n))
5421 If you use a function like @code{memchr}, @code{memset}, @code{strtok},
5422 or @code{strspn}, which have no @acronym{BSD} equivalent, then macros don't
5423 suffice to port to ancient hosts; you must provide an implementation of
5424 each function. An easy
5425 way to incorporate your implementations only when needed (since the ones
5426 in system C libraries may be hand optimized) is to, taking @code{memchr}
5427 for example, put it in @file{memchr.c} and use
5428 @samp{AC_REPLACE_FUNCS([memchr])}.
5431 @defmac AC_HEADER_SYS_WAIT
5432 @acindex{HEADER_SYS_WAIT}
5433 @cvindex HAVE_SYS_WAIT_H
5434 @hdrindex{sys/wait.h}
5435 If @file{sys/wait.h} exists and is compatible with Posix, define
5436 @code{HAVE_SYS_WAIT_H}. Incompatibility can occur if @file{sys/wait.h}
5437 does not exist, or if it uses the old @acronym{BSD} @code{union wait} instead
5438 of @code{int} to store a status value. If @file{sys/wait.h} is not
5439 Posix compatible, then instead of including it, define the
5440 Posix macros with their usual interpretations. Here is an
5445 #include <sys/types.h>
5446 #ifdef HAVE_SYS_WAIT_H
5447 # include <sys/wait.h>
5450 # define WEXITSTATUS(stat_val) ((unsigned int) (stat_val) >> 8)
5453 # define WIFEXITED(stat_val) (((stat_val) & 255) == 0)
5459 This macro is obsolescent, as current systems are compatible with Posix.
5460 New programs need not use this macro.
5463 @cvindex _POSIX_VERSION
5465 @code{_POSIX_VERSION} is defined when @file{unistd.h} is included on
5466 Posix systems. If there is no @file{unistd.h}, it is definitely
5467 not a Posix system. However, some non-Posix systems do
5468 have @file{unistd.h}.
5470 The way to check whether the system supports Posix is:
5474 #ifdef HAVE_UNISTD_H
5475 # include <sys/types.h>
5476 # include <unistd.h>
5479 #ifdef _POSIX_VERSION
5480 /* Code for Posix systems. */
5485 @defmac AC_HEADER_TIME
5486 @acindex{HEADER_TIME}
5487 @cvindex TIME_WITH_SYS_TIME
5489 @hdrindex{sys/time.h}
5490 If a program may include both @file{time.h} and @file{sys/time.h},
5491 define @code{TIME_WITH_SYS_TIME}. On some ancient systems,
5492 @file{sys/time.h} included @file{time.h}, but @file{time.h} was not
5493 protected against multiple inclusion, so programs could not explicitly
5494 include both files. This macro is useful in programs that use, for
5495 example, @code{struct timeval} as well as
5496 @code{struct tm}. It is best used in conjunction with
5497 @code{HAVE_SYS_TIME_H}, which can be checked for using
5498 @code{AC_CHECK_HEADERS([sys/time.h])}.
5502 #ifdef TIME_WITH_SYS_TIME
5503 # include <sys/time.h>
5506 # ifdef HAVE_SYS_TIME_H
5507 # include <sys/time.h>
5516 This macro is obsolescent, as current systems can include both files
5517 when they exist. New programs need not use this macro.
5521 @defmac AC_HEADER_TIOCGWINSZ
5522 @acindex{HEADER_TIOCGWINSZ}
5523 @cvindex GWINSZ_IN_SYS_IOCTL
5524 @hdrindex{sys/ioctl.h}
5525 @hdrindex{termios.h}
5526 @c FIXME: I need clarifications from Jim.
5527 If the use of @code{TIOCGWINSZ} requires @file{<sys/ioctl.h>}, then
5528 define @code{GWINSZ_IN_SYS_IOCTL}. Otherwise @code{TIOCGWINSZ} can be
5529 found in @file{<termios.h>}.
5535 #ifdef HAVE_TERMIOS_H
5536 # include <termios.h>
5539 #ifdef GWINSZ_IN_SYS_IOCTL
5540 # include <sys/ioctl.h>
5546 @node Generic Headers
5547 @subsection Generic Header Checks
5549 These macros are used to find system header files not covered by the
5550 ``particular'' test macros. If you need to check the contents of a header
5551 as well as find out whether it is present, you have to write your own
5552 test for it (@pxref{Writing Tests}).
5554 @defmac AC_CHECK_HEADER (@var{header-file}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes})
5555 @acindex{CHECK_HEADER}
5556 If the system header file @var{header-file} is compilable, execute shell
5557 commands @var{action-if-found}, otherwise execute
5558 @var{action-if-not-found}. If you just want to define a symbol if the
5559 header file is available, consider using @code{AC_CHECK_HEADERS}
5562 For compatibility issues with older versions of Autoconf, please read
5566 @defmac AC_CHECK_HEADERS (@var{header-file}@dots{}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes})
5567 @acindex{CHECK_HEADERS}
5568 @cvindex HAVE_@var{header}
5569 For each given system header file @var{header-file} in the
5570 blank-separated argument list that exists, define
5571 @code{HAVE_@var{header-file}} (in all capitals). If @var{action-if-found}
5572 is given, it is additional shell code to execute when one of the header
5573 files is found. You can give it a value of @samp{break} to break out of
5574 the loop on the first match. If @var{action-if-not-found} is given, it
5575 is executed when one of the header files is not found.
5577 For compatibility issues with older versions of Autoconf, please read
5581 Previous versions of Autoconf merely checked whether the header was
5582 accepted by the preprocessor. This was changed because the old test was
5583 inappropriate for typical uses. Headers are typically used to compile,
5584 not merely to preprocess, and the old behavior sometimes accepted
5585 headers that clashed at compile-time. If you need to check whether a
5586 header is preprocessable, you can use @code{AC_PREPROC_IFELSE}
5587 (@pxref{Running the Preprocessor}).
5589 This scheme, which improves the robustness of the test, also requires
5590 that you make sure that headers that must be included before the
5591 @var{header-file} be part of the @var{includes}, (@pxref{Default
5592 Includes}). If looking for @file{bar.h}, which requires that
5593 @file{foo.h} be included before if it exists, we suggest the following
5597 AC_CHECK_HEADERS([foo.h])
5598 AC_CHECK_HEADERS([bar.h], [], [],
5605 The following variant generates smaller, faster @command{configure}
5606 files if you do not need the full power of @code{AC_CHECK_HEADERS}.
5608 @defmac AC_CHECK_HEADERS_ONCE (@var{header-file}@dots{})
5609 @acindex{CHECK_HEADERS_ONCE}
5610 @cvindex HAVE_@var{header}
5611 For each given system header file @var{header-file} in the
5612 blank-separated argument list that exists, define
5613 @code{HAVE_@var{header-file}} (in all capitals).
5614 This is a once-only variant of @code{AC_CHECK_HEADERS}. It generates the
5615 checking code at most once, so that @command{configure} is smaller and
5616 faster; but the checks cannot be conditionalized and are always done once,
5617 early during the @command{configure} run.
5621 @section Declarations
5622 @cindex Declaration, checking
5624 The following macros check for the declaration of variables and
5625 functions. If there is no macro specifically defined to check for a
5626 symbol you need, then you can use the general macros (@pxref{Generic
5627 Declarations}) or, for more complex tests, you may use
5628 @code{AC_COMPILE_IFELSE} (@pxref{Running the Compiler}).
5631 * Particular Declarations:: Macros to check for certain declarations
5632 * Generic Declarations:: How to find other declarations
5635 @node Particular Declarations
5636 @subsection Particular Declaration Checks
5638 There are no specific macros for declarations.
5640 @node Generic Declarations
5641 @subsection Generic Declaration Checks
5643 These macros are used to find declarations not covered by the ``particular''
5646 @defmac AC_CHECK_DECL (@var{symbol}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes})
5647 @acindex{CHECK_DECL}
5648 If @var{symbol} (a function, variable, or constant) is not declared in
5649 @var{includes} and a declaration is needed, run the shell commands
5650 @var{action-if-not-found}, otherwise @var{action-if-found}. If no
5651 @var{includes} are specified, the default includes are used
5652 (@pxref{Default Includes}).
5654 This macro actually tests whether @var{symbol} is defined as a macro or
5655 can be used as an r-value, not whether it is really declared, because it
5656 is much safer to avoid
5657 introducing extra declarations when they are not needed.
5660 @defmac AC_CHECK_DECLS (@var{symbols}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes})
5661 @acindex{CHECK_DECLS}
5662 @cvindex HAVE_DECL_@var{symbol}
5663 For each of the @var{symbols} (@emph{comma}-separated list), define
5664 @code{HAVE_DECL_@var{symbol}} (in all capitals) to @samp{1} if
5665 @var{symbol} is declared, otherwise to @samp{0}. If
5666 @var{action-if-not-found} is given, it is additional shell code to
5667 execute when one of the function declarations is needed, otherwise
5668 @var{action-if-found} is executed.
5670 This macro uses an M4 list as first argument:
5672 AC_CHECK_DECLS([strdup])
5673 AC_CHECK_DECLS([strlen])
5674 AC_CHECK_DECLS([malloc, realloc, calloc, free])
5677 Unlike the other @samp{AC_CHECK_*S} macros, when a @var{symbol} is not
5678 declared, @code{HAVE_DECL_@var{symbol}} is defined to @samp{0} instead
5679 of leaving @code{HAVE_DECL_@var{symbol}} undeclared. When you are
5680 @emph{sure} that the check was performed, use
5681 @code{HAVE_DECL_@var{symbol}} in @code{#if}:
5684 #if !HAVE_DECL_SYMBOL
5685 extern char *symbol;
5690 If the test may have not been performed, however, because it is safer
5691 @emph{not} to declare a symbol than to use a declaration that conflicts
5692 with the system's one, you should use:
5695 #if defined HAVE_DECL_MALLOC && !HAVE_DECL_MALLOC
5696 void *malloc (size_t *s);
5701 You fall into the second category only in extreme situations: either
5702 your files may be used without being configured, or they are used during
5703 the configuration. In most cases the traditional approach is enough.
5706 @defmac AC_CHECK_DECLS_ONCE (@var{symbols})
5707 @acindex{CHECK_DECLS_ONCE}
5708 @cvindex HAVE_DECL_@var{symbol}
5709 For each of the @var{symbols} (@emph{comma}-separated list), define
5710 @code{HAVE_DECL_@var{symbol}} (in all capitals) to @samp{1} if
5711 @var{symbol} is declared in the default include files, otherwise to
5712 @samp{0}. This is a once-only variant of @code{AC_CHECK_DECLS}. It
5713 generates the checking code at most once, so that @command{configure} is
5714 smaller and faster; but the checks cannot be conditionalized and are
5715 always done once, early during the @command{configure} run.
5721 @cindex Structure, checking
5723 The following macros check for the presence of certain members in C
5724 structures. If there is no macro specifically defined to check for a
5725 member you need, then you can use the general structure-member macros
5726 (@pxref{Generic Structures}) or, for more complex tests, you may use
5727 @code{AC_COMPILE_IFELSE} (@pxref{Running the Compiler}).
5730 * Particular Structures:: Macros to check for certain structure members
5731 * Generic Structures:: How to find other structure members
5734 @node Particular Structures
5735 @subsection Particular Structure Checks
5737 The following macros check for certain structures or structure members.
5739 @defmac AC_STRUCT_DIRENT_D_INO
5740 @acindex{STRUCT_DIRENT_D_INO}
5741 @cvindex HAVE_STRUCT_DIRENT_D_INO
5742 Perform all the actions of @code{AC_HEADER_DIRENT} (@pxref{Particular
5743 Headers}). Then, if @code{struct dirent} contains a @code{d_ino}
5744 member, define @code{HAVE_STRUCT_DIRENT_D_INO}.
5746 @code{HAVE_STRUCT_DIRENT_D_INO} indicates only the presence of
5747 @code{d_ino}, not whether its contents are always reliable.
5748 Traditionally, a zero @code{d_ino} indicated a deleted directory entry,
5749 though current systems hide this detail from the user and never return
5750 zero @code{d_ino} values.
5751 Many current systems report an incorrect @code{d_ino} for a directory
5752 entry that is a mount point.
5755 @defmac AC_STRUCT_DIRENT_D_TYPE
5756 @acindex{STRUCT_DIRENT_D_TYPE}
5757 @cvindex HAVE_STRUCT_DIRENT_D_TYPE
5758 Perform all the actions of @code{AC_HEADER_DIRENT} (@pxref{Particular
5759 Headers}). Then, if @code{struct dirent} contains a @code{d_type}
5760 member, define @code{HAVE_STRUCT_DIRENT_D_TYPE}.
5763 @defmac AC_STRUCT_ST_BLKSIZE
5764 @acindex{STRUCT_ST_BLKSIZE}
5765 @cvindex HAVE_STRUCT_STAT_ST_BLKSIZE
5766 @cvindex HAVE_ST_BLKSIZE
5767 If @code{struct stat} contains an @code{st_blksize} member, define
5768 @code{HAVE_STRUCT_STAT_ST_BLKSIZE}. The former name,
5769 @code{HAVE_ST_BLKSIZE} is to be avoided, as its support will cease in
5770 the future. This macro is obsoleted, and should be replaced by
5773 AC_CHECK_MEMBERS([struct stat.st_blksize])
5777 @defmac AC_STRUCT_ST_BLOCKS
5778 @acindex{STRUCT_ST_BLOCKS}
5779 @cvindex HAVE_STRUCT_STAT_ST_BLOCKS
5780 @cvindex HAVE_ST_BLOCKS
5782 If @code{struct stat} contains an @code{st_blocks} member, define
5783 @code{HAVE_STRUCT_STAT_ST_BLOCKS}. Otherwise, require an
5784 @code{AC_LIBOBJ} replacement of @samp{fileblocks}. The former name,
5785 @code{HAVE_ST_BLOCKS} is to be avoided, as its support will cease in the
5789 @defmac AC_STRUCT_ST_RDEV
5790 @acindex{STRUCT_ST_RDEV}
5791 @cvindex HAVE_ST_RDEV
5792 @cvindex HAVE_STRUCT_STAT_ST_RDEV
5793 If @code{struct stat} contains an @code{st_rdev} member, define
5794 @code{HAVE_STRUCT_STAT_ST_RDEV}. The former name for this macro,
5795 @code{HAVE_ST_RDEV}, is to be avoided as it will cease to be supported
5796 in the future. Actually, even the new macro is obsolete and should be
5799 AC_CHECK_MEMBERS([struct stat.st_rdev])
5803 @defmac AC_STRUCT_TM
5805 @cvindex TM_IN_SYS_TIME
5807 @hdrindex{sys/time.h}
5808 If @file{time.h} does not define @code{struct tm}, define
5809 @code{TM_IN_SYS_TIME}, which means that including @file{sys/time.h}
5810 had better define @code{struct tm}.
5812 This macro is obsolescent, as @file{time.h} defines @code{struct tm} in
5813 current systems. New programs need not use this macro.
5816 @defmac AC_STRUCT_TIMEZONE
5817 @acindex{STRUCT_TIMEZONE}
5818 @cvindex HAVE_TM_ZONE
5819 @cvindex HAVE_TZNAME
5820 Figure out how to get the current timezone. If @code{struct tm} has a
5821 @code{tm_zone} member, define @code{HAVE_STRUCT_TM_TM_ZONE} (and the
5822 obsoleted @code{HAVE_TM_ZONE}). Otherwise, if the external array
5823 @code{tzname} is found, define @code{HAVE_TZNAME}; if it is declared,
5824 define @code{HAVE_DECL_TZNAME}.
5827 @node Generic Structures
5828 @subsection Generic Structure Checks
5830 These macros are used to find structure members not covered by the
5831 ``particular'' test macros.
5833 @defmac AC_CHECK_MEMBER (@var{aggregate}.@var{member}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes})
5834 @acindex{CHECK_MEMBER}
5835 Check whether @var{member} is a member of the aggregate @var{aggregate}.
5836 If no @var{includes} are specified, the default includes are used
5837 (@pxref{Default Includes}).
5840 AC_CHECK_MEMBER([struct passwd.pw_gecos], [],
5841 [AC_MSG_ERROR([We need `passwd.pw_gecos'!])],
5845 You can use this macro for submembers:
5848 AC_CHECK_MEMBER(struct top.middle.bot)
5852 @defmac AC_CHECK_MEMBERS (@var{members}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes})
5853 @acindex{CHECK_MEMBERS}
5854 Check for the existence of each @samp{@var{aggregate}.@var{member}} of
5855 @var{members} using the previous macro. When @var{member} belongs to
5856 @var{aggregate}, define @code{HAVE_@var{aggregate}_@var{member}} (in all
5857 capitals, with spaces and dots replaced by underscores). If
5858 @var{action-if-found} is given, it is executed for each of the found
5859 members. If @var{action-if-not-found} is given, it is executed for each
5860 of the members that could not be found.
5862 This macro uses M4 lists:
5864 AC_CHECK_MEMBERS([struct stat.st_rdev, struct stat.st_blksize])
5874 The following macros check for C types, either builtin or typedefs. If
5875 there is no macro specifically defined to check for a type you need, and
5876 you don't need to check for any special properties of it, then you can
5877 use a general type-check macro.
5880 * Particular Types:: Special handling to find certain types
5881 * Generic Types:: How to find other types
5884 @node Particular Types
5885 @subsection Particular Type Checks
5887 @hdrindex{sys/types.h}
5890 @hdrindex{inttypes.h}
5891 These macros check for particular C types in @file{sys/types.h},
5892 @file{stdlib.h}, @file{stdint.h}, @file{inttypes.h} and others, if they
5895 The Gnulib @code{stdint} module is an alternate way to define many of
5896 these symbols; it is useful if you prefer your code to assume a
5897 C99-or-better environment. @xref{Gnulib}.
5899 @defmac AC_TYPE_GETGROUPS
5900 @acindex{TYPE_GETGROUPS}
5901 @cvindex GETGROUPS_T
5902 Define @code{GETGROUPS_T} to be whichever of @code{gid_t} or @code{int}
5903 is the base type of the array argument to @code{getgroups}.
5906 @defmac AC_TYPE_INT8_T
5907 @acindex{TYPE_INT8_T}
5908 @cvindex HAVE_INT8_T
5910 If @file{stdint.h} or @file{inttypes.h} defines the type @code{int8_t},
5911 define @code{HAVE_INT8_T}. Otherwise, define @code{int8_t} to a signed
5912 integer type that is exactly 8 bits wide and that uses two's complement
5913 representation, if such a type exists.
5916 @defmac AC_TYPE_INT16_T
5917 @acindex{TYPE_INT16_T}
5918 @cvindex HAVE_INT16_T
5920 This is like @code{AC_TYPE_INT8_T}, except for 16-bit integers.
5923 @defmac AC_TYPE_INT32_T
5924 @acindex{TYPE_INT32_T}
5925 @cvindex HAVE_INT32_T
5927 This is like @code{AC_TYPE_INT8_T}, except for 32-bit integers.
5930 @defmac AC_TYPE_INT64_T
5931 @acindex{TYPE_INT64_T}
5932 @cvindex HAVE_INT64_T
5934 This is like @code{AC_TYPE_INT8_T}, except for 64-bit integers.
5937 @defmac AC_TYPE_INTMAX_T
5938 @acindex{TYPE_INTMAX_T}
5939 @cvindex HAVE_INTMAX_T
5941 If @file{stdint.h} or @file{inttypes.h} defines the type @code{intmax_t},
5942 define @code{HAVE_INTMAX_T}. Otherwise, define @code{intmax_t} to the
5943 widest signed integer type.
5946 @defmac AC_TYPE_INTPTR_T
5947 @acindex{TYPE_INTPTR_T}
5948 @cvindex HAVE_INTPTR_T
5950 If @file{stdint.h} or @file{inttypes.h} defines the type @code{intptr_t},
5951 define @code{HAVE_INTPTR_T}. Otherwise, define @code{intptr_t} to a
5952 signed integer type wide enough to hold a pointer, if such a type
5956 @defmac AC_TYPE_LONG_DOUBLE
5957 @acindex{TYPE_LONG_DOUBLE}
5958 @cvindex HAVE_LONG_DOUBLE
5959 If the C compiler supports a working @code{long double} type, define
5960 @code{HAVE_LONG_DOUBLE}. The @code{long double} type might have the
5961 same range and precision as @code{double}.
5963 This macro is obsolescent, as current C compilers support @code{long
5964 double}. New programs need not use this macro.
5967 @defmac AC_TYPE_LONG_DOUBLE_WIDER
5968 @acindex{TYPE_LONG_DOUBLE_WIDER}
5969 @cvindex HAVE_LONG_DOUBLE_WIDER
5970 If the C compiler supports a working @code{long double} type with more
5971 range or precision than the @code{double} type, define
5972 @code{HAVE_LONG_DOUBLE_WIDER}.
5975 @defmac AC_TYPE_LONG_LONG_INT
5976 @acindex{TYPE_LONG_LONG_INT}
5977 @cvindex HAVE_LONG_LONG_INT
5978 If the C compiler supports a working @code{long long int} type, define
5979 @code{HAVE_LONG_LONG_INT}.
5982 @defmac AC_TYPE_MBSTATE_T
5983 @acindex{TYPE_MBSTATE_T}
5986 Define @code{HAVE_MBSTATE_T} if @code{<wchar.h>} declares the
5987 @code{mbstate_t} type. Also, define @code{mbstate_t} to be a type if
5988 @code{<wchar.h>} does not declare it.
5991 @defmac AC_TYPE_MODE_T
5992 @acindex{TYPE_MODE_T}
5994 Define @code{mode_t} to a suitable type, if standard headers do not
5998 @defmac AC_TYPE_OFF_T
5999 @acindex{TYPE_OFF_T}
6001 Define @code{off_t} to a suitable type, if standard headers do not
6005 @defmac AC_TYPE_PID_T
6006 @acindex{TYPE_PID_T}
6008 Define @code{pid_t} to a suitable type, if standard headers do not
6012 @defmac AC_TYPE_SIGNAL
6013 @acindex{TYPE_SIGNAL}
6016 If @file{signal.h} declares @code{signal} as returning a pointer to a
6017 function returning @code{void}, define @code{RETSIGTYPE} to be
6018 @code{void}; otherwise, define it to be @code{int}.
6020 Define signal handlers as returning type @code{RETSIGTYPE}:
6033 @defmac AC_TYPE_SIZE_T
6034 @acindex{TYPE_SIZE_T}
6036 Define @code{size_t} to a suitable type, if standard headers do not
6040 @defmac AC_TYPE_SSIZE_T
6041 @acindex{TYPE_SSIZE_T}
6043 Define @code{ssize_t} to a suitable type, if standard headers do not
6047 @defmac AC_TYPE_UID_T
6048 @acindex{TYPE_UID_T}
6051 Define @code{uid_t} and @code{gid_t} to suitable types, if standard
6052 headers do not define them.
6055 @defmac AC_TYPE_UINT8_T
6056 @acindex{TYPE_UINT8_T}
6057 @cvindex HAVE_UINT8_T
6059 If @file{stdint.h} or @file{inttypes.h} defines the type @code{uint8_t},
6060 define @code{HAVE_UINT8_T}. Otherwise, define @code{uint8_t} to an
6061 unsigned integer type that is exactly 8 bits wide, if such a type
6065 @defmac AC_TYPE_UINT16_T
6066 @acindex{TYPE_UINT16_T}
6067 @cvindex HAVE_UINT16_T
6069 This is like @code{AC_TYPE_UINT8_T}, except for 16-bit unsigned integers.
6072 @defmac AC_TYPE_UINT32_T
6073 @acindex{TYPE_UINT32_T}
6074 @cvindex HAVE_UINT32_T
6076 This is like @code{AC_TYPE_UINT8_T}, except for 32-bit unsigned integers.
6079 @defmac AC_TYPE_UINT64_T
6080 @acindex{TYPE_UINT64_T}
6081 @cvindex HAVE_UINT64_T
6083 This is like @code{AC_TYPE_UINT8_T}, except for 64-bit unsigned integers.
6086 @defmac AC_TYPE_UINTMAX_T
6087 @acindex{TYPE_UINTMAX_T}
6088 @cvindex HAVE_UINTMAX_T
6090 If @file{stdint.h} or @file{inttypes.h} defines the type @code{uintmax_t},
6091 define @code{HAVE_UINTMAX_T}. Otherwise, define @code{uintmax_t} to the
6092 widest unsigned integer type.
6095 @defmac AC_TYPE_UINTPTR_T
6096 @acindex{TYPE_UINTPTR_T}
6097 @cvindex HAVE_UINTPTR_T
6099 If @file{stdint.h} or @file{inttypes.h} defines the type @code{uintptr_t},
6100 define @code{HAVE_UINTPTR_T}. Otherwise, define @code{uintptr_t} to an
6101 unsigned integer type wide enough to hold a pointer, if such a type
6105 @defmac AC_TYPE_UNSIGNED_LONG_LONG_INT
6106 @acindex{TYPE_UNSIGNED_LONG_LONG_INT}
6107 @cvindex HAVE_UNSIGNED_LONG_LONG_INT
6108 If the C compiler supports a working @code{unsigned long long int} type,
6109 define @code{HAVE_UNSIGNED_LONG_LONG_INT}.
6113 @subsection Generic Type Checks
6115 These macros are used to check for types not covered by the ``particular''
6118 @defmac AC_CHECK_TYPE (@var{type}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes})
6119 @acindex{CHECK_TYPE}
6120 Check whether @var{type} is defined. It may be a compiler builtin type
6121 or defined by the @var{includes} (@pxref{Default Includes}).
6123 In C, @var{type} must be a type-name, so that the expression @samp{sizeof
6124 (@var{type})} is valid (but @samp{sizeof ((@var{type}))} is not). The
6125 same test is applied when compiling for C++, which means that in C++
6126 @var{type} should be a type-id and should not be an anonymous
6127 @samp{struct} or @samp{union}.
6131 @defmac AC_CHECK_TYPES (@var{types}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes})
6132 @acindex{CHECK_TYPES}
6133 For each @var{type} of the @var{types} that is defined, define
6134 @code{HAVE_@var{type}} (in all capitals). Each @var{type} must follow
6135 the rules of @code{AC_CHECK_TYPE}. If no @var{includes} are
6136 specified, the default includes are used (@pxref{Default Includes}). If
6137 @var{action-if-found} is given, it is additional shell code to execute
6138 when one of the types is found. If @var{action-if-not-found} is given,
6139 it is executed when one of the types is not found.
6141 This macro uses M4 lists:
6143 AC_CHECK_TYPES([ptrdiff_t])
6144 AC_CHECK_TYPES([unsigned long long int, uintmax_t])
6149 Autoconf, up to 2.13, used to provide to another version of
6150 @code{AC_CHECK_TYPE}, broken by design. In order to keep backward
6151 compatibility, a simple heuristic, quite safe but not totally, is
6152 implemented. In case of doubt, read the documentation of the former
6153 @code{AC_CHECK_TYPE}, see @ref{Obsolete Macros}.
6156 @node Compilers and Preprocessors
6157 @section Compilers and Preprocessors
6159 @cindex Preprocessors
6162 All the tests for compilers (@code{AC_PROG_CC}, @code{AC_PROG_CXX},
6163 @code{AC_PROG_F77}) define the output variable @code{EXEEXT} based on
6164 the output of the compiler, typically to the empty string if
6165 Posix and @samp{.exe} if a @acronym{DOS} variant.
6168 They also define the output variable @code{OBJEXT} based on the
6169 output of the compiler, after @file{.c} files have been excluded, typically
6170 to @samp{o} if Posix, @samp{obj} if a @acronym{DOS} variant.
6172 If the compiler being used does not produce executables, the tests fail. If
6173 the executables can't be run, and cross-compilation is not enabled, they
6174 fail too. @xref{Manual Configuration}, for more on support for cross
6178 * Specific Compiler Characteristics:: Some portability issues
6179 * Generic Compiler Characteristics:: Language independent tests and features
6180 * C Compiler:: Checking its characteristics
6181 * C++ Compiler:: Likewise
6182 * Objective C Compiler:: Likewise
6183 * Erlang Compiler and Interpreter:: Likewise
6184 * Fortran Compiler:: Likewise
6187 @node Specific Compiler Characteristics
6188 @subsection Specific Compiler Characteristics
6190 Some compilers exhibit different behaviors.
6193 @item Static/Dynamic Expressions
6194 Autoconf relies on a trick to extract one bit of information from the C
6195 compiler: using negative array sizes. For instance the following
6196 excerpt of a C source demonstrates how to test whether @samp{int} objects are 4
6200 static int test_array[sizeof (int) == 4 ? 1 : -1];
6204 To our knowledge, there is a single compiler that does not support this
6205 trick: the @acronym{HP} C compilers (the real ones, not only the ``bundled'') on
6206 @acronym{HP-UX} 11.00.
6207 They incorrectly reject the above program with the diagnostic
6208 ``Variable-length arrays cannot have static storage.''
6209 This bug comes from @acronym{HP} compilers' mishandling of @code{sizeof (int)},
6210 not from the @code{? 1 : -1}, and
6211 Autoconf works around this problem by casting @code{sizeof (int)} to
6212 @code{long int} before comparing it.
6215 @node Generic Compiler Characteristics
6216 @subsection Generic Compiler Characteristics
6218 @defmac AC_CHECK_SIZEOF (@var{type-or-expr}, @ovar{unused}, @dvar{includes, default-includes})
6219 @acindex{CHECK_SIZEOF}
6220 Define @code{SIZEOF_@var{type-or-expr}} (@pxref{Standard Symbols}) to be
6221 the size in bytes of @var{type-or-expr}, which may be either a type or
6222 an expression returning a value that has a size. If the expression
6223 @samp{sizeof (@var{type-or-expr})} is invalid, the result is 0. If no
6224 @var{includes} are specified, the default includes are used
6225 (@pxref{Default Includes}).
6227 This macro now works even when cross-compiling. The @var{unused}
6228 argument was used when cross-compiling.
6230 For example, the call
6233 AC_CHECK_SIZEOF([int *])
6237 defines @code{SIZEOF_INT_P} to be 8 on DEC Alpha AXP systems.
6240 @defmac AC_CHECK_ALIGNOF (@var{type}, @dvar{includes, default-includes})
6241 @acindex{CHECK_ALIGNOF}
6242 Define @code{ALIGNOF_@var{type}} (@pxref{Standard Symbols}) to be the
6243 alignment in bytes of @var{type}. @samp{@var{type} y;} must be valid as
6244 a structure member declaration. If @samp{type} is unknown, the result
6245 is 0. If no @var{includes} are specified, the default includes are used
6246 (@pxref{Default Includes}).
6249 @defmac AC_COMPUTE_INT (@var{var}, @var{expression}, @dvar{includes, default-includes}, @ovar{action-if-fails})
6250 @acindex{COMPUTE_INT}
6251 Store into the shell variable @var{var} the value of the integer
6252 @var{expression}. The
6253 value should fit in an initializer in a C variable of type @code{signed
6254 long}. To support cross compilation (in which case, the macro only works on
6255 hosts that use twos-complement arithmetic), it should be possible to evaluate
6256 the expression at compile-time. If no @var{includes} are specified, the default
6257 includes are used (@pxref{Default Includes}).
6259 Execute @var{action-if-fails} if the value cannot be determined correctly.
6262 @defmac AC_LANG_WERROR
6263 @acindex{LANG_WERROR}
6264 Normally Autoconf ignores warnings generated by the compiler, linker, and
6265 preprocessor. If this macro is used, warnings count as fatal
6266 errors for the current language. This macro is useful when the
6267 results of configuration are used where warnings are unacceptable; for
6268 instance, if parts of a program are built with the @acronym{GCC}
6270 option. If the whole program is built using @option{-Werror} it is
6271 often simpler to put @option{-Werror} in the compiler flags (@code{CFLAGS},
6276 @subsection C Compiler Characteristics
6278 The following macros provide ways to find and exercise a C Compiler.
6279 There are a few constructs that ought to be avoided, but do not deserve
6280 being checked for, since they can easily be worked around.
6283 @item Don't use lines containing solitary backslashes
6284 They tickle a bug in the @acronym{HP-UX} C compiler (checked on
6285 @acronym{HP-UX} 10.20,
6286 11.00, and 11i). When given the following source:
6291 * A comment with backslash-newlines in it. %@{ %@} *\
6295 " A string with backslash-newlines in it %@{ %@} \\
6297 char apostrophe = '\\
6305 the compiler incorrectly fails with the diagnostics ``Non-terminating
6306 comment at end of file'' and ``Missing @samp{#endif} at end of file.''
6307 Removing the lines with solitary backslashes solves the problem.
6309 @item Don't compile several files at once if output matters to you
6310 Some compilers, such as @acronym{HP}'s, report names of files being
6311 compiled when given more than one file operand. For instance:
6320 This can cause problems if you observe the output of the compiler to
6321 detect failures. Invoking @samp{cc -c a.c && cc -c b.c && cc -o c a.o
6322 b.o} solves the issue.
6324 @item Don't rely on @code{#error} failing
6325 The @sc{irix} C compiler does not fail when #error is preprocessed; it
6326 simply emits a diagnostic and continues, exiting successfully. So,
6327 instead of an error directive like @code{#error "Unsupported word size"}
6328 it is more portable to use an invalid directive like @code{#Unsupported
6329 word size} in Autoconf tests. In ordinary source code, @code{#error} is
6330 OK, since installers with inadequate compilers like @sc{irix} can simply
6331 examine these compilers' diagnostic output.
6333 @item Don't rely on correct @code{#line} support
6334 On Solaris, @command{c89} (at least Sun C 5.3 through 5.8)
6335 diagnoses @code{#line} directives whose line
6336 numbers are greater than 32767. Nothing in Posix
6337 makes this invalid. That is why Autoconf stopped issuing
6338 @code{#line} directives.
6341 @defmac AC_PROG_CC (@ovar{compiler-search-list})
6345 Determine a C compiler to use. If @code{CC} is not already set in the
6346 environment, check for @code{gcc} and @code{cc}, then for other C
6347 compilers. Set output variable @code{CC} to the name of the compiler
6350 This macro may, however, be invoked with an optional first argument
6351 which, if specified, must be a blank-separated list of C compilers to
6352 search for. This just gives the user an opportunity to specify an
6353 alternative search list for the C compiler. For example, if you didn't
6354 like the default order, then you could invoke @code{AC_PROG_CC} like
6358 AC_PROG_CC([gcc cl cc])
6361 If the C compiler does not handle function prototypes correctly by
6362 default, try to add an option to output variable @code{CC} to make it
6363 so. This macro tries various options that select standard-conformance
6364 modes on various systems.
6366 After calling this macro you can check whether the C compiler has been
6367 set to accept @acronym{ANSI} C89 (@acronym{ISO} C90); if not, the shell
6369 @code{ac_cv_prog_cc_c89} is set to @samp{no}. See also
6370 @code{AC_C_PROTOTYPES} below.
6372 If using the @acronym{GNU} C compiler, set shell variable @code{GCC} to
6373 @samp{yes}. If output variable @code{CFLAGS} was not already set, set
6374 it to @option{-g -O2} for the @acronym{GNU} C compiler (@option{-O2} on systems
6375 where @acronym{GCC} does not accept @option{-g}), or @option{-g} for
6379 @defmac AC_PROG_CC_C_O
6380 @acindex{PROG_CC_C_O}
6381 @cvindex NO_MINUS_C_MINUS_O
6382 If the C compiler does not accept the @option{-c} and @option{-o} options
6383 simultaneously, define @code{NO_MINUS_C_MINUS_O}. This macro actually
6384 tests both the compiler found by @code{AC_PROG_CC}, and, if different,
6385 the first @code{cc} in the path. The test fails if one fails. This
6386 macro was created for @acronym{GNU} Make to choose the default C compilation
6394 Set output variable @code{CPP} to a command that runs the
6395 C preprocessor. If @samp{$CC -E} doesn't work, @file{/lib/cpp} is used.
6396 It is only portable to run @code{CPP} on files with a @file{.c}
6399 Some preprocessors don't indicate missing include files by the error
6400 status. For such preprocessors an internal variable is set that causes
6401 other macros to check the standard error from the preprocessor and
6402 consider the test failed if any warnings have been reported.
6403 For most preprocessors, though, warnings do not cause include-file
6404 tests to fail unless @code{AC_PROG_CPP_WERROR} is also specified.
6407 @defmac AC_PROG_CPP_WERROR
6408 @acindex{PROG_CPP_WERROR}
6410 This acts like @code{AC_PROG_CPP}, except it treats warnings from the
6411 preprocessor as errors even if the preprocessor exit status indicates
6412 success. This is useful for avoiding headers that generate mandatory
6413 warnings, such as deprecation notices.
6417 The following macros check for C compiler or machine architecture
6418 features. To check for characteristics not listed here, use
6419 @code{AC_COMPILE_IFELSE} (@pxref{Running the Compiler}) or
6420 @code{AC_RUN_IFELSE} (@pxref{Runtime}).
6422 @defmac AC_PROG_CC_STDC
6423 @acindex{PROG_CC_STDC}
6424 If the C compiler cannot compile @acronym{ISO} Standard C (currently
6425 C99), try to add an option to output variable @code{CC} to make it work.
6426 If the compiler does not support C99, fall back to supporting
6427 @acronym{ANSI} C89 (@acronym{ISO} C90).
6429 After calling this macro you can check whether the C compiler has been
6430 set to accept Standard C; if not, the shell variable
6431 @code{ac_cv_prog_cc_stdc} is set to @samp{no}.
6434 @defmac AC_PROG_CC_C89
6435 @acindex{PROG_CC_C89}
6436 If the C compiler is not in @acronym{ANSI} C89 (@acronym{ISO} C90) mode by
6437 default, try to add an option to output variable @code{CC} to make it
6438 so. This macro tries various options that select @acronym{ANSI} C89 on
6439 some system or another. It considers the compiler to be in
6440 @acronym{ANSI} C89 mode if it handles function prototypes correctly.
6442 After calling this macro you can check whether the C compiler has been
6443 set to accept @acronym{ANSI} C89; if not, the shell variable
6444 @code{ac_cv_prog_cc_c89} is set to @samp{no}.
6446 This macro is called automatically by @code{AC_PROG_CC}.
6449 @defmac AC_PROG_CC_C99
6450 @acindex{PROG_CC_C99}
6451 If the C compiler is not in C99 mode by default, try to add an
6452 option to output variable @code{CC} to make it so. This macro tries
6453 various options that select C99 on some system or another. It
6454 considers the compiler to be in C99 mode if it handles @code{_Bool},
6455 @code{//} comments, flexible array members, @code{inline}, signed and
6456 unsigned @code{long long int}, mixed code and declarations, named
6457 initialization of structs,
6458 @code{restrict}, @code{va_copy}, varargs macros, variable declarations
6459 in @code{for} loops, and variable length arrays.
6461 After calling this macro you can check whether the C compiler has been
6462 set to accept C99; if not, the shell variable
6463 @code{ac_cv_prog_cc_c99} is set to @samp{no}.
6466 @defmac AC_C_BACKSLASH_A
6467 @acindex{HAVE_C_BACKSLASH_A}
6468 Define @samp{HAVE_C_BACKSLASH_A} to 1 if the C compiler understands
6471 This macro is obsolescent, as current C compilers understand @samp{\a}.
6472 New programs need not use this macro.
6475 @defmac AC_C_BIGENDIAN (@ovar{action-if-true}, @ovar{action-if-false}, @ovar{action-if-unknown}, @ovar{action-if-universal})
6476 @acindex{C_BIGENDIAN}
6477 @cvindex WORDS_BIGENDIAN
6479 If words are stored with the most significant byte first (like Motorola
6480 and SPARC CPUs), execute @var{action-if-true}. If words are stored with
6481 the least significant byte first (like Intel and VAX CPUs), execute
6482 @var{action-if-false}.
6484 This macro runs a test-case if endianness cannot be determined from the
6485 system header files. When cross-compiling, the test-case is not run but
6486 grep'ed for some magic values. @var{action-if-unknown} is executed if
6487 the latter case fails to determine the byte sex of the host system.
6489 In some cases a single run of a compiler can generate code for multiple
6490 architectures. This can happen, for example, when generating Mac OS X
6491 universal binary files, which work on both PowerPC and Intel
6492 architectures. In this case, the different variants might be for
6493 different architectures whose endiannesses differ. If
6494 @command{configure} detects this, it executes @var{action-if-universal}
6495 instead of @var{action-if-unknown}.
6497 The default for @var{action-if-true} is to define
6498 @samp{WORDS_BIGENDIAN}. The default for @var{action-if-false} is to do
6499 nothing. The default for @var{action-if-unknown} is to
6500 abort configure and tell the installer how to bypass this test.
6501 And finally, the default for @var{action-if-universal} is to define
6502 @samp{WORDS_BIGENDIAN} or not, depending on the architecture that the
6503 code is being generated for.
6505 If you use this macro without specifying @var{action-if-universal}, you
6506 should also use @code{AC_CONFIG_HEADERS}; otherwise
6507 @samp{WORDS_BIGENDIAN} may be set incorrectly for Mac OS X universal
6514 If the C compiler does not fully support the @code{const} keyword,
6515 define @code{const} to be empty. Some C compilers that do
6516 not define @code{__STDC__} do support @code{const}; some compilers that
6517 define @code{__STDC__} do not completely support @code{const}. Programs
6518 can simply use @code{const} as if every C compiler supported it; for
6519 those that don't, the makefile or configuration header file
6520 defines it as empty.
6522 Occasionally installers use a C++ compiler to compile C code, typically
6523 because they lack a C compiler. This causes problems with @code{const},
6524 because C and C++ treat @code{const} differently. For example:
6531 is valid in C but not in C++. These differences unfortunately cannot be
6532 papered over by defining @code{const} to be empty.
6534 If @command{autoconf} detects this situation, it leaves @code{const} alone,
6535 as this generally yields better results in practice. However, using a
6536 C++ compiler to compile C code is not recommended or supported, and
6537 installers who run into trouble in this area should get a C compiler
6538 like @acronym{GCC} to compile their C code.
6540 This macro is obsolescent, as current C compilers support @code{const}.
6541 New programs need not use this macro.
6544 @defmac AC_C_RESTRICT
6545 @acindex{C_RESTRICT}
6547 If the C compiler recognizes a variant spelling for the @code{restrict}
6548 keyword (@code{__restrict}, @code{__restrict__}, or @code{_Restrict}),
6549 then define @code{restrict} to that; this is more likely to do the right
6550 thing with compilers that support language variants where plain
6551 @code{restrict} is not a keyword. Otherwise, if the C compiler
6552 recognizes the @code{restrict} keyword, don't do anything.
6553 Otherwise, define @code{restrict} to be empty.
6554 Thus, programs may simply use @code{restrict} as if every C compiler
6555 supported it; for those that do not, the makefile
6556 or configuration header defines it away.
6558 Although support in C++ for the @code{restrict} keyword is not
6559 required, several C++ compilers do accept the keyword.
6560 This macro works for them, too.
6563 @defmac AC_C_VOLATILE
6564 @acindex{C_VOLATILE}
6566 If the C compiler does not understand the keyword @code{volatile},
6567 define @code{volatile} to be empty. Programs can simply use
6568 @code{volatile} as if every C compiler supported it; for those that do
6569 not, the makefile or configuration header defines it as
6572 If the correctness of your program depends on the semantics of
6573 @code{volatile}, simply defining it to be empty does, in a sense, break
6574 your code. However, given that the compiler does not support
6575 @code{volatile}, you are at its mercy anyway. At least your
6576 program compiles, when it wouldn't before.
6577 @xref{Volatile Objects}, for more about @code{volatile}.
6579 In general, the @code{volatile} keyword is a standard C feature, so
6580 you might expect that @code{volatile} is available only when
6581 @code{__STDC__} is defined. However, Ultrix 4.3's native compiler does
6582 support volatile, but does not define @code{__STDC__}.
6584 This macro is obsolescent, as current C compilers support @code{volatile}.
6585 New programs need not use this macro.
6591 If the C compiler supports the keyword @code{inline}, do nothing.
6592 Otherwise define @code{inline} to @code{__inline__} or @code{__inline}
6593 if it accepts one of those, otherwise define @code{inline} to be empty.
6599 OpenMP (@url{http://www.openmp.org/}) specifies extensions of the C,
6600 C++, and Fortran languages that simplify optimization of shared memory
6601 parallelism, which is a common problem on multicore CPUs.
6603 The macro @code{AC_C_OPENMP} sets the variable @code{OPENMP_CFLAGS} to
6604 the C compiler flags needed for supporting OpenMP@.
6605 @code{OPENMP_CFLAGS} is set to empty if the compiler already supports
6606 OpenMP, if it has no way to activate OpenMP support, or if the user
6607 rejects OpenMP support by invoking @samp{configure} with the
6608 @samp{--disable-openmp} option.
6610 @code{OPENMP_CFLAGS} needs to be used when compiling programs, when
6611 preprocessing program source, and when linking programs. Therefore you
6612 need to add @code{$(OPENMP_CFLAGS)} to the @code{CFLAGS} of programs
6613 that use OpenMP@. If you preprocess OpenMP-specific code, you also need
6614 to add @code{$(OPENMP_CFLAGS)} to @code{CPPFLAGS}. The presence of
6615 OpenMP support is revealed at compile time by the preprocessor macro
6618 Linking a program with @code{OPENMP_CFLAGS} typically adds one more
6619 shared library to the program's dependencies, so its use is recommended
6620 only on programs that actually require OpenMP.
6623 @defmac AC_C_CHAR_UNSIGNED
6624 @acindex{C_CHAR_UNSIGNED}
6625 @cvindex __CHAR_UNSIGNED__
6626 If the C type @code{char} is unsigned, define @code{__CHAR_UNSIGNED__},
6627 unless the C compiler predefines it.
6630 @defmac AC_C_STRINGIZE
6631 @acindex{C_STRINGIZE}
6632 @cvindex HAVE_STRINGIZE
6633 If the C preprocessor supports the stringizing operator, define
6634 @code{HAVE_STRINGIZE}. The stringizing operator is @samp{#} and is
6635 found in macros such as this:
6641 This macro is obsolescent, as current C compilers support the
6642 stringizing operator. New programs need not use this macro.
6645 @defmac AC_C_FLEXIBLE_ARRAY_MEMBER
6646 @acindex{C_FLEXIBLE_ARRAY_MEMBER}
6647 @cvindex FLEXIBLE_ARRAY_MEMBER
6648 If the C compiler supports flexible array members, define
6649 @code{FLEXIBLE_ARRAY_MEMBER} to nothing; otherwise define it to 1.
6650 That way, a declaration like this:
6656 double val[FLEXIBLE_ARRAY_MEMBER];
6661 will let applications use the ``struct hack'' even with compilers that
6662 do not support flexible array members. To allocate and use such an
6663 object, you can use code like this:
6667 size_t n = compute_value_count ();
6669 malloc (offsetof (struct s, val)
6670 + n * sizeof (double));
6672 for (i = 0; i < n; i++)
6673 p->val[i] = compute_value (i);
6677 @defmac AC_C_VARARRAYS
6678 @acindex{C_VARARRAYS}
6679 @cvindex HAVE_C_VARARRAYS
6680 If the C compiler supports variable-length arrays, define
6681 @code{HAVE_C_VARARRAYS}. A variable-length array is an array of automatic
6682 storage duration whose length is determined at run time, when the array
6688 @cvindex HAVE_TYPEOF
6690 If the C compiler supports @acronym{GCC}'s @code{typeof} syntax either
6692 through a different spelling of the keyword (e.g., @code{__typeof__}),
6693 define @code{HAVE_TYPEOF}. If the support is available only through a
6694 different spelling, define @code{typeof} to that spelling.
6697 @defmac AC_C_PROTOTYPES
6698 @acindex{C_PROTOTYPES}
6700 @cvindex __PROTOTYPES
6702 If function prototypes are understood by the compiler (as determined by
6703 @code{AC_PROG_CC}), define @code{PROTOTYPES} and @code{__PROTOTYPES}.
6704 Defining @code{__PROTOTYPES} is for the benefit of
6705 header files that cannot use macros that infringe on user name space.
6707 This macro is obsolescent, as current C compilers support prototypes.
6708 New programs need not use this macro.
6711 @defmac AC_PROG_GCC_TRADITIONAL
6712 @acindex{PROG_GCC_TRADITIONAL}
6714 Add @option{-traditional} to output variable @code{CC} if using the
6715 @acronym{GNU} C compiler and @code{ioctl} does not work properly without
6716 @option{-traditional}. That usually happens when the fixed header files
6717 have not been installed on an old system.
6719 This macro is obsolescent, since current versions of the @acronym{GNU} C
6720 compiler fix the header files automatically when installed.
6725 @subsection C++ Compiler Characteristics
6728 @defmac AC_PROG_CXX (@ovar{compiler-search-list})
6732 Determine a C++ compiler to use. Check whether the environment variable
6733 @code{CXX} or @code{CCC} (in that order) is set; if so, then set output
6734 variable @code{CXX} to its value.
6736 Otherwise, if the macro is invoked without an argument, then search for
6737 a C++ compiler under the likely names (first @code{g++} and @code{c++}
6738 then other names). If none of those checks succeed, then as a last
6739 resort set @code{CXX} to @code{g++}.
6741 This macro may, however, be invoked with an optional first argument
6742 which, if specified, must be a blank-separated list of C++ compilers to
6743 search for. This just gives the user an opportunity to specify an
6744 alternative search list for the C++ compiler. For example, if you
6745 didn't like the default order, then you could invoke @code{AC_PROG_CXX}
6749 AC_PROG_CXX([gcc cl KCC CC cxx cc++ xlC aCC c++ g++])
6752 If using the @acronym{GNU} C++ compiler, set shell variable @code{GXX} to
6753 @samp{yes}. If output variable @code{CXXFLAGS} was not already set, set
6754 it to @option{-g -O2} for the @acronym{GNU} C++ compiler (@option{-O2} on
6755 systems where G++ does not accept @option{-g}), or @option{-g} for other
6759 @defmac AC_PROG_CXXCPP
6760 @acindex{PROG_CXXCPP}
6762 Set output variable @code{CXXCPP} to a command that runs the C++
6763 preprocessor. If @samp{$CXX -E} doesn't work, @file{/lib/cpp} is used.
6764 It is portable to run @code{CXXCPP} only on files with a @file{.c},
6765 @file{.C}, @file{.cc}, or @file{.cpp} extension.
6767 Some preprocessors don't indicate missing include files by the error
6768 status. For such preprocessors an internal variable is set that causes
6769 other macros to check the standard error from the preprocessor and
6770 consider the test failed if any warnings have been reported. However,
6771 it is not known whether such broken preprocessors exist for C++.
6774 @defmac AC_PROG_CXX_C_O
6775 @acindex{PROG_CXX_C_O}
6776 @cvindex CXX_NO_MINUS_C_MINUS_O
6777 Test whether the C++ compiler accepts the options @option{-c} and
6778 @option{-o} simultaneously, and define @code{CXX_NO_MINUS_C_MINUS_O},
6783 @node Objective C Compiler
6784 @subsection Objective C Compiler Characteristics
6787 @defmac AC_PROG_OBJC (@ovar{compiler-search-list})
6791 Determine an Objective C compiler to use. If @code{OBJC} is not already
6792 set in the environment, check for Objective C compilers. Set output
6793 variable @code{OBJC} to the name of the compiler found.
6795 This macro may, however, be invoked with an optional first argument
6796 which, if specified, must be a blank-separated list of Objective C compilers to
6797 search for. This just gives the user an opportunity to specify an
6798 alternative search list for the Objective C compiler. For example, if you
6799 didn't like the default order, then you could invoke @code{AC_PROG_OBJC}
6803 AC_PROG_OBJC([gcc objcc objc])
6806 If using the @acronym{GNU} Objective C compiler, set shell variable
6807 @code{GOBJC} to @samp{yes}. If output variable @code{OBJCFLAGS} was not
6808 already set, set it to @option{-g -O2} for the @acronym{GNU} Objective C
6809 compiler (@option{-O2} on systems where @command{gcc} does not accept
6810 @option{-g}), or @option{-g} for other compilers.
6813 @defmac AC_PROG_OBJCPP
6814 @acindex{PROG_OBJCPP}
6816 Set output variable @code{OBJCPP} to a command that runs the Objective C
6817 preprocessor. If @samp{$OBJC -E} doesn't work, @file{/lib/cpp} is used.
6821 @node Erlang Compiler and Interpreter
6822 @subsection Erlang Compiler and Interpreter Characteristics
6825 Autoconf defines the following macros for determining paths to the essential
6826 Erlang/OTP programs:
6828 @defmac AC_ERLANG_PATH_ERLC (@ovar{value-if-not-found}, @ovar{path})
6829 @acindex{ERLANG_PATH_ERLC}
6832 Determine an Erlang compiler to use. If @code{ERLC} is not already set in the
6833 environment, check for @command{erlc}. Set output variable @code{ERLC} to the
6834 complete path of the compiler command found. In addition, if @code{ERLCFLAGS}
6835 is not set in the environment, set it to an empty value.
6837 The two optional arguments have the same meaning as the two last arguments of
6838 macro @code{AC_PROG_PATH} for looking for the @command{erlc} program. For
6839 example, to look for @command{erlc} only in the @file{/usr/lib/erlang/bin}
6843 AC_ERLANG_PATH_ERLC([not found], [/usr/lib/erlang/bin])
6847 @defmac AC_ERLANG_NEED_ERLC (@ovar{path})
6848 @acindex{ERLANG_NEED_ERLC}
6849 A simplified variant of the @code{AC_ERLANG_PATH_ERLC} macro, that prints an
6850 error message and exits the @command{configure} script if the @command{erlc}
6851 program is not found.
6854 @defmac AC_ERLANG_PATH_ERL (@ovar{value-if-not-found}, @ovar{path})
6855 @acindex{ERLANG_PATH_ERL}
6857 Determine an Erlang interpreter to use. If @code{ERL} is not already set in the
6858 environment, check for @command{erl}. Set output variable @code{ERL} to the
6859 complete path of the interpreter command found.
6861 The two optional arguments have the same meaning as the two last arguments of
6862 macro @code{AC_PROG_PATH} for looking for the @command{erl} program. For
6863 example, to look for @command{erl} only in the @file{/usr/lib/erlang/bin}
6867 AC_ERLANG_PATH_ERL([not found], [/usr/lib/erlang/bin])
6871 @defmac AC_ERLANG_NEED_ERL (@ovar{path})
6872 @acindex{ERLANG_NEED_ERL}
6873 A simplified variant of the @code{AC_ERLANG_PATH_ERL} macro, that prints an
6874 error message and exits the @command{configure} script if the @command{erl}
6875 program is not found.
6879 @node Fortran Compiler
6880 @subsection Fortran Compiler Characteristics
6884 The Autoconf Fortran support is divided into two categories: legacy
6885 Fortran 77 macros (@code{F77}), and modern Fortran macros (@code{FC}).
6886 The former are intended for traditional Fortran 77 code, and have output
6887 variables like @code{F77}, @code{FFLAGS}, and @code{FLIBS}. The latter
6888 are for newer programs that can (or must) compile under the newer
6889 Fortran standards, and have output variables like @code{FC},
6890 @code{FCFLAGS}, and @code{FCLIBS}.
6892 Except for two new macros @code{AC_FC_SRCEXT} and
6893 @code{AC_FC_FREEFORM} (see below), the @code{FC} and @code{F77} macros
6894 behave almost identically, and so they are documented together in this
6898 @defmac AC_PROG_F77 (@ovar{compiler-search-list})
6902 Determine a Fortran 77 compiler to use. If @code{F77} is not already
6903 set in the environment, then check for @code{g77} and @code{f77}, and
6904 then some other names. Set the output variable @code{F77} to the name
6905 of the compiler found.
6907 This macro may, however, be invoked with an optional first argument
6908 which, if specified, must be a blank-separated list of Fortran 77
6909 compilers to search for. This just gives the user an opportunity to
6910 specify an alternative search list for the Fortran 77 compiler. For
6911 example, if you didn't like the default order, then you could invoke
6912 @code{AC_PROG_F77} like this:
6915 AC_PROG_F77([fl32 f77 fort77 xlf g77 f90 xlf90])
6918 If using @code{g77} (the @acronym{GNU} Fortran 77 compiler), then
6919 set the shell variable @code{G77} to @samp{yes}.
6920 If the output variable @code{FFLAGS} was not already set in the
6921 environment, then set it to @option{-g -02} for @code{g77} (or @option{-O2}
6922 where @code{g77} does not accept @option{-g}). Otherwise, set
6923 @code{FFLAGS} to @option{-g} for all other Fortran 77 compilers.
6926 @defmac AC_PROG_FC (@ovar{compiler-search-list}, @ovar{dialect})
6930 Determine a Fortran compiler to use. If @code{FC} is not already set in
6931 the environment, then @code{dialect} is a hint to indicate what Fortran
6932 dialect to search for; the default is to search for the newest available
6933 dialect. Set the output variable @code{FC} to the name of the compiler
6936 By default, newer dialects are preferred over older dialects, but if
6937 @code{dialect} is specified then older dialects are preferred starting
6938 with the specified dialect. @code{dialect} can currently be one of
6939 Fortran 77, Fortran 90, or Fortran 95. However, this is only a hint of
6940 which compiler @emph{name} to prefer (e.g., @code{f90} or @code{f95}),
6941 and no attempt is made to guarantee that a particular language standard
6942 is actually supported. Thus, it is preferable that you avoid the
6943 @code{dialect} option, and use AC_PROG_FC only for code compatible with
6944 the latest Fortran standard.
6946 This macro may, alternatively, be invoked with an optional first argument
6947 which, if specified, must be a blank-separated list of Fortran
6948 compilers to search for, just as in @code{AC_PROG_F77}.
6950 If the output variable @code{FCFLAGS} was not already set in the
6951 environment, then set it to @option{-g -02} for @acronym{GNU} @code{g77} (or
6952 @option{-O2} where @code{g77} does not accept @option{-g}). Otherwise,
6953 set @code{FCFLAGS} to @option{-g} for all other Fortran compilers.
6956 @defmac AC_PROG_F77_C_O
6957 @defmacx AC_PROG_FC_C_O
6958 @acindex{PROG_F77_C_O}
6959 @acindex{PROG_FC_C_O}
6960 @cvindex F77_NO_MINUS_C_MINUS_O
6961 @cvindex FC_NO_MINUS_C_MINUS_O
6962 Test whether the Fortran compiler accepts the options @option{-c} and
6963 @option{-o} simultaneously, and define @code{F77_NO_MINUS_C_MINUS_O} or
6964 @code{FC_NO_MINUS_C_MINUS_O}, respectively, if it does not.
6967 The following macros check for Fortran compiler characteristics.
6968 To check for characteristics not listed here, use
6969 @code{AC_COMPILE_IFELSE} (@pxref{Running the Compiler}) or
6970 @code{AC_RUN_IFELSE} (@pxref{Runtime}), making sure to first set the
6971 current language to Fortran 77 or Fortran via @code{AC_LANG([Fortran 77])}
6972 or @code{AC_LANG(Fortran)} (@pxref{Language Choice}).
6975 @defmac AC_F77_LIBRARY_LDFLAGS
6976 @defmacx AC_FC_LIBRARY_LDFLAGS
6977 @acindex{F77_LIBRARY_LDFLAGS}
6979 @acindex{FC_LIBRARY_LDFLAGS}
6981 Determine the linker flags (e.g., @option{-L} and @option{-l}) for the
6982 @dfn{Fortran intrinsic and runtime libraries} that are required to
6983 successfully link a Fortran program or shared library. The output
6984 variable @code{FLIBS} or @code{FCLIBS} is set to these flags (which
6985 should be included after @code{LIBS} when linking).
6987 This macro is intended to be used in those situations when it is
6988 necessary to mix, e.g., C++ and Fortran source code in a single
6989 program or shared library (@pxref{Mixing Fortran 77 With C and C++, , ,
6990 automake, @acronym{GNU} Automake}).
6992 For example, if object files from a C++ and Fortran compiler must be
6993 linked together, then the C++ compiler/linker must be used for linking
6994 (since special C++-ish things need to happen at link time like calling
6995 global constructors, instantiating templates, enabling exception
6998 However, the Fortran intrinsic and runtime libraries must be linked in
6999 as well, but the C++ compiler/linker doesn't know by default how to add
7000 these Fortran 77 libraries. Hence, this macro was created to determine
7001 these Fortran libraries.
7003 The macros @code{AC_F77_DUMMY_MAIN} and @code{AC_FC_DUMMY_MAIN} or
7004 @code{AC_F77_MAIN} and @code{AC_FC_MAIN} are probably also necessary to
7005 link C/C++ with Fortran; see below.
7008 @defmac AC_F77_DUMMY_MAIN (@ovar{action-if-found}, @ovar{action-if-not-found})
7009 @defmacx AC_FC_DUMMY_MAIN (@ovar{action-if-found}, @ovar{action-if-not-found})
7010 @acindex{F77_DUMMY_MAIN}
7011 @cvindex F77_DUMMY_MAIN
7012 With many compilers, the Fortran libraries detected by
7013 @code{AC_F77_LIBRARY_LDFLAGS} or @code{AC_FC_LIBRARY_LDFLAGS} provide
7014 their own @code{main} entry function that initializes things like
7015 Fortran I/O, and which then calls a user-provided entry function named
7016 (say) @code{MAIN__} to run the user's program. The
7017 @code{AC_F77_DUMMY_MAIN} and @code{AC_FC_DUMMY_MAIN} or
7018 @code{AC_F77_MAIN} and @code{AC_FC_MAIN} macros figure out how to deal with
7021 When using Fortran for purely numerical functions (no I/O, etc.)@: often
7022 one prefers to provide one's own @code{main} and skip the Fortran
7023 library initializations. In this case, however, one may still need to
7024 provide a dummy @code{MAIN__} routine in order to prevent linking errors
7025 on some systems. @code{AC_F77_DUMMY_MAIN} or @code{AC_FC_DUMMY_MAIN}
7026 detects whether any such routine is @emph{required} for linking, and
7027 what its name is; the shell variable @code{F77_DUMMY_MAIN} or
7028 @code{FC_DUMMY_MAIN} holds this name, @code{unknown} when no solution
7029 was found, and @code{none} when no such dummy main is needed.
7031 By default, @var{action-if-found} defines @code{F77_DUMMY_MAIN} or
7032 @code{FC_DUMMY_MAIN} to the name of this routine (e.g., @code{MAIN__})
7033 @emph{if} it is required. @var{action-if-not-found} defaults to
7034 exiting with an error.
7036 In order to link with Fortran routines, the user's C/C++ program should
7037 then include the following code to define the dummy main if it is
7041 #ifdef F77_DUMMY_MAIN
7045 int F77_DUMMY_MAIN() @{ return 1; @}
7049 (Replace @code{F77} with @code{FC} for Fortran instead of Fortran 77.)
7051 Note that this macro is called automatically from @code{AC_F77_WRAPPERS}
7052 or @code{AC_FC_WRAPPERS}; there is generally no need to call it
7053 explicitly unless one wants to change the default actions.
7062 As discussed above, many Fortran libraries allow you to provide an entry
7063 point called (say) @code{MAIN__} instead of the usual @code{main}, which
7064 is then called by a @code{main} function in the Fortran libraries that
7065 initializes things like Fortran I/O@. The
7066 @code{AC_F77_MAIN} and @code{AC_FC_MAIN} macros detect whether it is
7067 @emph{possible} to utilize such an alternate main function, and defines
7068 @code{F77_MAIN} and @code{FC_MAIN} to the name of the function. (If no
7069 alternate main function name is found, @code{F77_MAIN} and @code{FC_MAIN} are
7070 simply defined to @code{main}.)
7072 Thus, when calling Fortran routines from C that perform things like I/O,
7073 one should use this macro and name the "main" function
7074 @code{F77_MAIN} or @code{FC_MAIN} instead of @code{main}.
7077 @defmac AC_F77_WRAPPERS
7078 @defmacx AC_FC_WRAPPERS
7079 @acindex{F77_WRAPPERS}
7082 @acindex{FC_WRAPPERS}
7085 Defines C macros @code{F77_FUNC (name, NAME)}, @code{FC_FUNC (name, NAME)},
7086 @code{F77_FUNC_(name, NAME)}, and @code{FC_FUNC_(name, NAME)} to properly
7087 mangle the names of C/C++ identifiers, and identifiers with underscores,
7088 respectively, so that they match the name-mangling scheme used by the
7091 Fortran is case-insensitive, and in order to achieve this the Fortran
7092 compiler converts all identifiers into a canonical case and format. To
7093 call a Fortran subroutine from C or to write a C function that is
7094 callable from Fortran, the C program must explicitly use identifiers in
7095 the format expected by the Fortran compiler. In order to do this, one
7096 simply wraps all C identifiers in one of the macros provided by
7097 @code{AC_F77_WRAPPERS} or @code{AC_FC_WRAPPERS}. For example, suppose
7098 you have the following Fortran 77 subroutine:
7101 subroutine foobar (x, y)
7102 double precision x, y
7108 You would then declare its prototype in C or C++ as:
7111 #define FOOBAR_F77 F77_FUNC (foobar, FOOBAR)
7113 extern "C" /* prevent C++ name mangling */
7115 void FOOBAR_F77(double *x, double *y);
7118 Note that we pass both the lowercase and uppercase versions of the
7119 function name to @code{F77_FUNC} so that it can select the right one.
7120 Note also that all parameters to Fortran 77 routines are passed as
7121 pointers (@pxref{Mixing Fortran 77 With C and C++, , , automake, @acronym{GNU}
7124 (Replace @code{F77} with @code{FC} for Fortran instead of Fortran 77.)
7126 Although Autoconf tries to be intelligent about detecting the
7127 name-mangling scheme of the Fortran compiler, there may be Fortran
7128 compilers that it doesn't support yet. In this case, the above code
7129 generates a compile-time error, but some other behavior
7130 (e.g., disabling Fortran-related features) can be induced by checking
7131 whether @code{F77_FUNC} or @code{FC_FUNC} is defined.
7133 Now, to call that routine from a C program, we would do something like:
7137 double x = 2.7183, y;
7138 FOOBAR_F77 (&x, &y);
7142 If the Fortran identifier contains an underscore (e.g., @code{foo_bar}),
7143 you should use @code{F77_FUNC_} or @code{FC_FUNC_} instead of
7144 @code{F77_FUNC} or @code{FC_FUNC} (with the same arguments). This is
7145 because some Fortran compilers mangle names differently if they contain
7149 @defmac AC_F77_FUNC (@var{name}, @ovar{shellvar})
7150 @defmacx AC_FC_FUNC (@var{name}, @ovar{shellvar})
7153 Given an identifier @var{name}, set the shell variable @var{shellvar} to
7154 hold the mangled version @var{name} according to the rules of the
7155 Fortran linker (see also @code{AC_F77_WRAPPERS} or
7156 @code{AC_FC_WRAPPERS}). @var{shellvar} is optional; if it is not
7157 supplied, the shell variable is simply @var{name}. The purpose of
7158 this macro is to give the caller a way to access the name-mangling
7159 information other than through the C preprocessor as above, for example,
7160 to call Fortran routines from some language other than C/C++.
7163 @defmac AC_FC_SRCEXT (@var{ext}, @ovar{action-if-success}, @ovar{action-if-failure})
7165 By default, the @code{FC} macros perform their tests using a @file{.f}
7166 extension for source-code files. Some compilers, however, only enable
7167 newer language features for appropriately named files, e.g., Fortran 90
7168 features only for @file{.f90} files. On the other hand, some other
7169 compilers expect all source files to end in @file{.f} and require
7170 special flags to support other file name extensions. The
7171 @code{AC_FC_SRCEXT} macro deals with both of these issues.
7173 The @code{AC_FC_SRCEXT} tries to get the @code{FC} compiler to accept files
7174 ending with the extension .@var{ext} (i.e., @var{ext} does @emph{not}
7175 contain the dot). If any special compiler flags are needed for this, it
7176 stores them in the output variable @code{FCFLAGS_}@var{ext}. This
7177 extension and these flags are then used for all subsequent @code{FC} tests
7178 (until @code{AC_FC_SRCEXT} is called again).
7180 For example, you would use @code{AC_FC_SRCEXT(f90)} to employ the
7181 @file{.f90} extension in future tests, and it would set a
7182 @code{FCFLAGS_f90} output variable with any extra flags that are needed
7183 to compile such files.
7185 The @code{FCFLAGS_}@var{ext} can @emph{not} be simply absorbed into
7186 @code{FCFLAGS}, for two reasons based on the limitations of some
7187 compilers. First, only one @code{FCFLAGS_}@var{ext} can be used at a
7188 time, so files with different extensions must be compiled separately.
7189 Second, @code{FCFLAGS_}@var{ext} must appear @emph{immediately} before
7190 the source-code file name when compiling. So, continuing the example
7191 above, you might compile a @file{foo.f90} file in your makefile with the
7196 $(FC) -c $(FCFLAGS) $(FCFLAGS_f90) '$(srcdir)/foo.f90'
7199 If @code{AC_FC_SRCEXT} succeeds in compiling files with the @var{ext}
7200 extension, it calls @var{action-if-success} (defaults to nothing). If
7201 it fails, and cannot find a way to make the @code{FC} compiler accept such
7202 files, it calls @var{action-if-failure} (defaults to exiting with an
7207 @defmac AC_FC_FREEFORM (@ovar{action-if-success}, @ovar{action-if-failure})
7208 @acindex{FC_FREEFORM}
7210 The @code{AC_FC_FREEFORM} tries to ensure that the Fortran compiler
7211 (@code{$FC}) allows free-format source code (as opposed to the older
7212 fixed-format style from Fortran 77). If necessary, it may add some
7213 additional flags to @code{FCFLAGS}.
7215 This macro is most important if you are using the default @file{.f}
7216 extension, since many compilers interpret this extension as indicating
7217 fixed-format source unless an additional flag is supplied. If you
7218 specify a different extension with @code{AC_FC_SRCEXT}, such as
7219 @file{.f90} or @file{.f95}, then @code{AC_FC_FREEFORM} ordinarily
7220 succeeds without modifying @code{FCFLAGS}.
7222 If @code{AC_FC_FREEFORM} succeeds in compiling free-form source, it
7223 calls @var{action-if-success} (defaults to nothing). If it fails, it
7224 calls @var{action-if-failure} (defaults to exiting with an error
7228 @node System Services
7229 @section System Services
7231 The following macros check for operating system services or capabilities.
7236 @cindex X Window System
7237 Try to locate the X Window System include files and libraries. If the
7238 user gave the command line options @option{--x-includes=@var{dir}} and
7239 @option{--x-libraries=@var{dir}}, use those directories.
7241 If either or both were not given, get the missing values by running
7242 @code{xmkmf} (or an executable pointed to by the @code{XMKMF}
7243 environment variable) on a trivial @file{Imakefile} and examining the
7244 makefile that it produces. Setting @code{XMKMF} to @samp{false}
7245 disables this method.
7247 If this method fails to find the X Window System, @command{configure}
7248 looks for the files in several directories where they often reside.
7249 If either method is successful, set the shell variables
7250 @code{x_includes} and @code{x_libraries} to their locations, unless they
7251 are in directories the compiler searches by default.
7253 If both methods fail, or the user gave the command line option
7254 @option{--without-x}, set the shell variable @code{no_x} to @samp{yes};
7255 otherwise set it to the empty string.
7258 @defmac AC_PATH_XTRA
7262 @ovindex X_EXTRA_LIBS
7264 @cvindex X_DISPLAY_MISSING
7265 An enhanced version of @code{AC_PATH_X}. It adds the C compiler flags
7266 that X needs to output variable @code{X_CFLAGS}, and the X linker flags
7267 to @code{X_LIBS}. Define @code{X_DISPLAY_MISSING} if X is not
7270 This macro also checks for special libraries that some systems need in
7271 order to compile X programs. It adds any that the system needs to
7272 output variable @code{X_EXTRA_LIBS}. And it checks for special X11R6
7273 libraries that need to be linked with before @option{-lX11}, and adds
7274 any found to the output variable @code{X_PRE_LIBS}.
7276 @c This is an incomplete kludge. Make a real way to do it.
7277 @c If you need to check for other X functions or libraries yourself, then
7278 @c after calling this macro, add the contents of @code{X_EXTRA_LIBS} to
7279 @c @code{LIBS} temporarily, like this: (FIXME - add example)
7282 @defmac AC_SYS_INTERPRETER
7283 @acindex{SYS_INTERPRETER}
7284 Check whether the system supports starting scripts with a line of the
7285 form @samp{#!/bin/sh} to select the interpreter to use for the script.
7286 After running this macro, shell code in @file{configure.ac} can check
7287 the shell variable @code{interpval}; it is set to @samp{yes}
7288 if the system supports @samp{#!}, @samp{no} if not.
7291 @defmac AC_SYS_LARGEFILE
7292 @acindex{SYS_LARGEFILE}
7293 @cvindex _FILE_OFFSET_BITS
7294 @cvindex _LARGE_FILES
7296 @cindex Large file support
7299 @uref{http://www.unix-systems.org/@/version2/@/whatsnew/@/lfs20mar.html,
7300 large-file support}. On some hosts, one must use special compiler
7301 options to build programs that can access large files. Append any such
7302 options to the output variable @code{CC}. Define
7303 @code{_FILE_OFFSET_BITS} and @code{_LARGE_FILES} if necessary.
7305 Large-file support can be disabled by configuring with the
7306 @option{--disable-largefile} option.
7308 If you use this macro, check that your program works even when
7309 @code{off_t} is wider than @code{long int}, since this is common when
7310 large-file support is enabled. For example, it is not correct to print
7311 an arbitrary @code{off_t} value @code{X} with @code{printf ("%ld",
7314 The LFS introduced the @code{fseeko} and @code{ftello} functions to
7315 replace their C counterparts @code{fseek} and @code{ftell} that do not
7316 use @code{off_t}. Take care to use @code{AC_FUNC_FSEEKO} to make their
7317 prototypes available when using them and large-file support is
7321 @defmac AC_SYS_LONG_FILE_NAMES
7322 @acindex{SYS_LONG_FILE_NAMES}
7323 @cvindex HAVE_LONG_FILE_NAMES
7324 If the system supports file names longer than 14 characters, define
7325 @code{HAVE_LONG_FILE_NAMES}.
7328 @defmac AC_SYS_POSIX_TERMIOS
7329 @acindex{SYS_POSIX_TERMIOS}
7330 @cindex Posix termios headers
7331 @cindex termios Posix headers
7332 Check to see if the Posix termios headers and functions are available on the
7333 system. If so, set the shell variable @code{ac_cv_sys_posix_termios} to
7334 @samp{yes}. If not, set the variable to @samp{no}.
7337 @node Posix Variants
7338 @section Posix Variants
7340 The following macros check for certain operating systems that need
7341 special treatment for some programs, due to exceptional oddities in
7342 their header files or libraries. These macros are warts; they will be
7343 replaced by a more systematic approach, based on the functions they make
7344 available or the environments they provide.
7348 @cvindex _ALL_SOURCE
7349 If on @acronym{AIX}, define @code{_ALL_SOURCE}.
7350 Allows the use of some @acronym{BSD}
7351 functions. Should be called before any macros that run the C compiler.
7354 @defmac AC_GNU_SOURCE
7355 @acindex{GNU_SOURCE}
7356 @cvindex _GNU_SOURCE
7357 If using the @acronym{GNU} C library, define @code{_GNU_SOURCE}.
7358 Allows the use of some @acronym{GNU} functions. Should be called
7359 before any macros that run the C compiler.
7362 @defmac AC_ISC_POSIX
7365 For @sc{interactive} Systems Corporation Unix, add @option{-lcposix} to output
7366 variable @code{LIBS} if necessary for Posix facilities. Call this
7367 after @code{AC_PROG_CC} and before any other macros that use Posix
7370 This macro is obsolescent, as @sc{interactive} Unix is obsolete, and Sun
7371 dropped support for it on 2006-07-23. New programs need not use this
7378 @cvindex _POSIX_SOURCE
7379 @cvindex _POSIX_1_SOURCE
7380 If on Minix, define @code{_MINIX} and @code{_POSIX_SOURCE} and define
7381 @code{_POSIX_1_SOURCE} to be 2. This allows the use of Posix
7382 facilities. Should be called before any macros that run the C compiler.
7385 @defmac AC_USE_SYSTEM_EXTENSIONS
7386 @acindex{USE_SYSTEM_EXTENSIONS}
7387 @cvindex _ALL_SOURCE
7388 @cvindex _GNU_SOURCE
7390 @cvindex _POSIX_1_SOURCE
7391 @cvindex _POSIX_PTHREAD_SEMANTICS
7392 @cvindex _POSIX_SOURCE
7393 @cvindex _TANDEM_SOURCE
7394 @cvindex __EXTENSIONS__
7395 If possible, enable extensions to Posix on hosts that normally disable
7396 the extensions, typically due to standards-conformance namespace issues.
7397 This may involve defining @code{__EXTENSIONS__} and
7398 @code{_POSIX_PTHREAD_SEMANTICS}, which are macros used by Solaris.
7399 It also defines @code{_TANDEM_SOURCE} for the @acronym{HP} NonStop platform.
7400 This macro also has the combined effects of @code{AC_GNU_SOURCE},
7401 @code{AC_AIX}, and @code{AC_MINIX}.
7405 @node Erlang Libraries
7406 @section Erlang Libraries
7407 @cindex Erlang, Library, checking
7409 The following macros check for an installation of Erlang/OTP, and for the
7410 presence of certain Erlang libraries. All those macros require the
7411 configuration of an Erlang interpreter and an Erlang compiler
7412 (@pxref{Erlang Compiler and Interpreter}).
7414 @defmac AC_ERLANG_SUBST_ROOT_DIR
7415 @acindex{ERLANG_SUBST_ROOT_DIR}
7416 @ovindex ERLANG_ROOT_DIR
7418 Set the output variable @code{ERLANG_ROOT_DIR} to the path to the base directory
7419 in which Erlang/OTP is installed (as returned by Erlang's @code{code:root_dir/0}
7420 function). The result of this test is cached if caching is enabled when running
7421 @command{configure}.
7424 @defmac AC_ERLANG_SUBST_LIB_DIR
7425 @acindex{ERLANG_SUBST_LIB_DIR}
7426 @ovindex ERLANG_LIB_DIR
7428 Set the output variable @code{ERLANG_LIB_DIR} to the path of the library
7429 directory of Erlang/OTP (as returned by Erlang's
7430 @code{code:lib_dir/0} function), which subdirectories each contain an installed
7431 Erlang/OTP library. The result of this test is cached if caching is enabled
7432 when running @command{configure}.
7435 @defmac AC_ERLANG_CHECK_LIB (@var{library}, @ovar{action-if-found}, @ovar{action-if-not-found})
7436 @acindex{ERLANG_CHECK_LIB}
7437 @ovindex ERLANG_LIB_DIR_@var{library}
7438 @ovindex ERLANG_LIB_VER_@var{library}
7440 Test whether the Erlang/OTP library @var{library} is installed by
7441 calling Erlang's @code{code:lib_dir/1} function. The result of this
7442 test is cached if caching is enabled when running @command{configure}.
7443 @var{action-if-found} is a list of shell commands to run if the library
7444 is installed; @var{action-if-not-found} is a list of shell commands to
7445 run if it is not. Additionally, if the library is installed, the output
7446 variable @samp{ERLANG_LIB_DIR_@var{library}} is set to the path to the
7447 library installation directory, and the output variable
7448 @samp{ERLANG_LIB_VER_@var{library}} is set to the version number that is
7449 part of the subdirectory name, if it is in the standard form
7450 (@code{@var{library}-@var{version}}). If the directory name does not
7451 have a version part, @samp{ERLANG_LIB_VER_@var{library}} is set to the
7452 empty string. If the library is not installed,
7453 @samp{ERLANG_LIB_DIR_@var{library}} and
7454 @samp{ERLANG_LIB_VER_@var{library}} are set to @code{"not found"}. For
7455 example, to check if library @code{stdlib} is installed:
7458 AC_ERLANG_CHECK_LIB([stdlib],
7459 [echo "stdlib version \"$ERLANG_LIB_VER_stdlib\""
7460 echo "is installed in \"$ERLANG_LIB_DIR_stdlib\""],
7461 [AC_MSG_ERROR([stdlib was not found!])])
7465 In addition to the above macros, which test installed Erlang libraries, the
7466 following macros determine the paths to the directories into which newly built
7467 Erlang libraries are to be installed:
7469 @defmac AC_ERLANG_SUBST_INSTALL_LIB_DIR
7470 @acindex{ERLANG_SUBST_INSTALL_LIB_DIR}
7471 @ovindex ERLANG_INSTALL_LIB_DIR
7473 Set the @code{ERLANG_INSTALL_LIB_DIR} output variable to the directory into
7474 which every built Erlang library should be installed in a separate subdirectory.
7475 If this variable is not set in the environment when @command{configure} runs,
7476 its default value is @code{$ERLANG_LIB_DIR}, which value is set by the
7477 @code{AC_ERLANG_SUBST_LIB_DIR} macro.
7480 @defmac AC_ERLANG_SUBST_INSTALL_LIB_SUBDIR (@var{library}, @var{version})
7481 @acindex{ERLANG_SUBST_INSTALL_LIB_SUBDIR}
7482 @ovindex ERLANG_INSTALL_LIB_DIR_@var{library}
7484 Set the @samp{ERLANG_INSTALL_LIB_DIR_@var{library}} output variable to the
7485 directory into which the built Erlang library @var{library} version
7486 @var{version} should be installed. If this variable is not set in the
7487 environment when @command{configure} runs, its default value is
7488 @samp{$ERLANG_INSTALL_LIB_DIR/@var{library}-@var{version}}, the value of the
7489 @code{ERLANG_INSTALL_LIB_DIR} variable being set by the
7490 @code{AC_ERLANG_SUBST_INSTALL_LIB_DIR} macro.
7497 @c ========================================================= Writing Tests
7500 @chapter Writing Tests
7502 If the existing feature tests don't do something you need, you have to
7503 write new ones. These macros are the building blocks. They provide
7504 ways for other macros to check whether various kinds of features are
7505 available and report the results.
7507 This chapter contains some suggestions and some of the reasons why the
7508 existing tests are written the way they are. You can also learn a lot
7509 about how to write Autoconf tests by looking at the existing ones. If
7510 something goes wrong in one or more of the Autoconf tests, this
7511 information can help you understand the assumptions behind them, which
7512 might help you figure out how to best solve the problem.
7514 These macros check the output of the compiler system of the current
7515 language (@pxref{Language Choice}). They do not cache the results of
7516 their tests for future use (@pxref{Caching Results}), because they don't
7517 know enough about the information they are checking for to generate a
7518 cache variable name. They also do not print any messages, for the same
7519 reason. The checks for particular kinds of features call these macros
7520 and do cache their results and print messages about what they're
7523 When you write a feature test that could be applicable to more than one
7524 software package, the best thing to do is encapsulate it in a new macro.
7525 @xref{Writing Autoconf Macros}, for how to do that.
7528 * Language Choice:: Selecting which language to use for testing
7529 * Writing Test Programs:: Forging source files for compilers
7530 * Running the Preprocessor:: Detecting preprocessor symbols
7531 * Running the Compiler:: Detecting language or header features
7532 * Running the Linker:: Detecting library features
7533 * Runtime:: Testing for runtime features
7534 * Systemology:: A zoology of operating systems
7535 * Multiple Cases:: Tests for several possible values
7538 @node Language Choice
7539 @section Language Choice
7542 Autoconf-generated @command{configure} scripts check for the C compiler and
7543 its features by default. Packages that use other programming languages
7544 (maybe more than one, e.g., C and C++) need to test features of the
7545 compilers for the respective languages. The following macros determine
7546 which programming language is used in the subsequent tests in
7547 @file{configure.ac}.
7549 @defmac AC_LANG (@var{language})
7550 Do compilation tests using the compiler, preprocessor, and file
7551 extensions for the specified @var{language}.
7553 Supported languages are:
7557 Do compilation tests using @code{CC} and @code{CPP} and use extension
7558 @file{.c} for test programs. Use compilation flags: @code{CPPFLAGS} with
7559 @code{CPP}, and both @code{CPPFLAGS} and @code{CFLAGS} with @code{CC}.
7562 Do compilation tests using @code{CXX} and @code{CXXCPP} and use
7563 extension @file{.C} for test programs. Use compilation flags:
7564 @code{CPPFLAGS} with @code{CXXCPP}, and both @code{CPPFLAGS} and
7565 @code{CXXFLAGS} with @code{CXX}.
7568 Do compilation tests using @code{F77} and use extension @file{.f} for
7569 test programs. Use compilation flags: @code{FFLAGS}.
7572 Do compilation tests using @code{FC} and use extension @file{.f} (or
7573 whatever has been set by @code{AC_FC_SRCEXT}) for test programs. Use
7574 compilation flags: @code{FCFLAGS}.
7580 Compile and execute tests using @code{ERLC} and @code{ERL} and use extension
7581 @file{.erl} for test Erlang modules. Use compilation flags: @code{ERLCFLAGS}.
7584 Do compilation tests using @code{OBJC} and @code{OBJCPP} and use
7585 extension @file{.m} for test programs. Use compilation flags:
7586 @code{CPPFLAGS} with @code{OBJCPP}, and both @code{CPPFLAGS} and
7587 @code{OBJCFLAGS} with @code{OBJC}.
7591 @defmac AC_LANG_PUSH (@var{language})
7593 Remember the current language (as set by @code{AC_LANG}) on a stack, and
7594 then select the @var{language}. Use this macro and @code{AC_LANG_POP}
7595 in macros that need to temporarily switch to a particular language.
7598 @defmac AC_LANG_POP (@ovar{language})
7600 Select the language that is saved on the top of the stack, as set by
7601 @code{AC_LANG_PUSH}, and remove it from the stack.
7603 If given, @var{language} specifies the language we just @emph{quit}. It
7604 is a good idea to specify it when it's known (which should be the
7605 case@dots{}), since Autoconf detects inconsistencies.
7608 AC_LANG_PUSH([Fortran 77])
7609 # Perform some tests on Fortran 77.
7611 AC_LANG_POP([Fortran 77])
7615 @defmac AC_LANG_ASSERT (@var{language})
7616 @acindex{LANG_ASSERT} Check statically that the current language is
7617 @var{language}. You should use this in your language specific macros
7618 to avoid that they be called with an inappropriate language.
7620 This macro runs only at @command{autoconf} time, and incurs no cost at
7621 @command{configure} time. Sadly enough and because Autoconf is a two
7622 layer language @footnote{Because M4 is not aware of Sh code,
7623 especially conditionals, some optimizations that look nice statically
7624 may produce incorrect results at runtime.}, the macros
7625 @code{AC_LANG_PUSH} and @code{AC_LANG_POP} cannot be ``optimizing'',
7626 therefore as much as possible you ought to avoid using them to wrap
7627 your code, rather, require from the user to run the macro with a
7628 correct current language, and check it with @code{AC_LANG_ASSERT}.
7629 And anyway, that may help the user understand she is running a Fortran
7630 macro while expecting a result about her Fortran 77 compiler@dots{}
7634 @defmac AC_REQUIRE_CPP
7635 @acindex{REQUIRE_CPP}
7636 Ensure that whichever preprocessor would currently be used for tests has
7637 been found. Calls @code{AC_REQUIRE} (@pxref{Prerequisite Macros}) with an
7638 argument of either @code{AC_PROG_CPP} or @code{AC_PROG_CXXCPP},
7639 depending on which language is current.
7643 @node Writing Test Programs
7644 @section Writing Test Programs
7646 Autoconf tests follow a common scheme: feed some program with some
7647 input, and most of the time, feed a compiler with some source file.
7648 This section is dedicated to these source samples.
7651 * Guidelines:: General rules for writing test programs
7652 * Test Functions:: Avoiding pitfalls in test programs
7653 * Generating Sources:: Source program boilerplate
7657 @subsection Guidelines for Test Programs
7659 The most important rule to follow when writing testing samples is:
7661 @center @emph{Look for realism.}
7663 This motto means that testing samples must be written with the same
7664 strictness as real programs are written. In particular, you should
7665 avoid ``shortcuts'' and simplifications.
7667 Don't just play with the preprocessor if you want to prepare a
7668 compilation. For instance, using @command{cpp} to check whether a header is
7669 functional might let your @command{configure} accept a header which
7670 causes some @emph{compiler} error. Do not hesitate to check a header with
7671 other headers included before, especially required headers.
7673 Make sure the symbols you use are properly defined, i.e., refrain for
7674 simply declaring a function yourself instead of including the proper
7677 Test programs should not write to standard output. They
7678 should exit with status 0 if the test succeeds, and with status 1
7679 otherwise, so that success
7680 can be distinguished easily from a core dump or other failure;
7681 segmentation violations and other failures produce a nonzero exit
7682 status. Unless you arrange for @code{exit} to be declared, test
7683 programs should @code{return}, not @code{exit}, from @code{main},
7684 because on many systems @code{exit} is not declared by default.
7686 Test programs can use @code{#if} or @code{#ifdef} to check the values of
7687 preprocessor macros defined by tests that have already run. For
7688 example, if you call @code{AC_HEADER_STDBOOL}, then later on in
7689 @file{configure.ac} you can have a test program that includes
7690 @file{stdbool.h} conditionally:
7694 #ifdef HAVE_STDBOOL_H
7695 # include <stdbool.h>
7700 Both @code{#if HAVE_STDBOOL_H} and @code{#ifdef HAVE_STDBOOL_H} will
7701 work with any standard C compiler. Some developers prefer @code{#if}
7702 because it is easier to read, while others prefer @code{#ifdef} because
7703 it avoids diagnostics with picky compilers like @acronym{GCC} with the
7704 @option{-Wundef} option.
7706 If a test program needs to use or create a data file, give it a name
7707 that starts with @file{conftest}, such as @file{conftest.data}. The
7708 @command{configure} script cleans up by running @samp{rm -f -r conftest*}
7709 after running test programs and if the script is interrupted.
7711 @node Test Functions
7712 @subsection Test Functions
7714 These days it's safe to assume support for function prototypes
7715 (introduced in C89).
7717 Functions that test programs declare should also be conditionalized for
7718 C++, which requires @samp{extern "C"} prototypes. Make sure to not
7719 include any header files containing clashing prototypes.
7725 void *valloc (size_t);
7728 If a test program calls a function with invalid parameters (just to see
7729 whether it exists), organize the program to ensure that it never invokes
7730 that function. You can do this by calling it in another function that is
7731 never invoked. You can't do it by putting it after a call to
7732 @code{exit}, because @acronym{GCC} version 2 knows that @code{exit}
7734 and optimizes out any code that follows it in the same block.
7736 If you include any header files, be sure to call the functions
7737 relevant to them with the correct number of arguments, even if they are
7738 just 0, to avoid compilation errors due to prototypes. @acronym{GCC}
7740 has internal prototypes for several functions that it automatically
7741 inlines; for example, @code{memcpy}. To avoid errors when checking for
7742 them, either pass them the correct number of arguments or redeclare them
7743 with a different return type (such as @code{char}).
7746 @node Generating Sources
7747 @subsection Generating Sources
7749 Autoconf provides a set of macros that can be used to generate test
7750 source files. They are written to be language generic, i.e., they
7751 actually depend on the current language (@pxref{Language Choice}) to
7752 ``format'' the output properly.
7755 @defmac AC_LANG_CONFTEST (@var{source})
7756 @acindex{LANG_CONFTEST}
7757 Save the @var{source} text in the current test source file:
7758 @file{conftest.@var{extension}} where the @var{extension} depends on the
7761 Note that the @var{source} is evaluated exactly once, like regular
7762 Autoconf macro arguments, and therefore (i) you may pass a macro
7763 invocation, (ii) if not, be sure to double quote if needed.
7766 @defmac AC_LANG_SOURCE (@var{source})
7767 @acindex{LANG_SOURCE}
7768 Expands into the @var{source}, with the definition of
7769 all the @code{AC_DEFINE} performed so far.
7772 For instance executing (observe the double quotation!):
7775 AC_INIT([Hello], [1.0], [bug-hello@@example.org])
7776 AC_DEFINE([HELLO_WORLD], ["Hello, World\n"],
7777 [Greetings string.])
7780 [AC_LANG_SOURCE([[const char hw[] = "Hello, World\n";]])])
7781 gcc -E -dD -o - conftest.c
7791 #define PACKAGE_NAME "Hello"
7792 #define PACKAGE_TARNAME "hello"
7793 #define PACKAGE_VERSION "1.0"
7794 #define PACKAGE_STRING "Hello 1.0"
7795 #define PACKAGE_BUGREPORT "bug-hello@@example.org"
7796 #define HELLO_WORLD "Hello, World\n"
7798 const char hw[] = "Hello, World\n";
7801 When the test language is Fortran or Erlang, the @code{AC_DEFINE} definitions
7802 are not automatically translated into constants in the source code by this
7805 @defmac AC_LANG_PROGRAM (@var{prologue}, @var{body})
7806 @acindex{LANG_PROGRAM}
7807 Expands into a source file which consists of the @var{prologue}, and
7808 then @var{body} as body of the main function (e.g., @code{main} in
7809 C). Since it uses @code{AC_LANG_SOURCE}, the features of the latter are
7816 AC_INIT([Hello], [1.0], [bug-hello@@example.org])
7817 AC_DEFINE([HELLO_WORLD], ["Hello, World\n"],
7818 [Greetings string.])
7820 [AC_LANG_PROGRAM([[const char hw[] = "Hello, World\n";]],
7821 [[fputs (hw, stdout);]])])
7822 gcc -E -dD -o - conftest.c
7832 #define PACKAGE_NAME "Hello"
7833 #define PACKAGE_TARNAME "hello"
7834 #define PACKAGE_VERSION "1.0"
7835 #define PACKAGE_STRING "Hello 1.0"
7836 #define PACKAGE_BUGREPORT "bug-hello@@example.org"
7837 #define HELLO_WORLD "Hello, World\n"
7839 const char hw[] = "Hello, World\n";
7849 In Erlang tests, the created source file is that of an Erlang module called
7850 @code{conftest} (@file{conftest.erl}). This module defines and exports at least
7851 one @code{start/0} function, which is called to perform the test. The
7852 @var{prologue} is optional code that is inserted between the module header and
7853 the @code{start/0} function definition. @var{body} is the body of the
7854 @code{start/0} function without the final period (@pxref{Runtime}, about
7855 constraints on this function's behavior).
7860 AC_INIT([Hello], [1.0], [bug-hello@@example.org])
7863 [AC_LANG_PROGRAM([[-define(HELLO_WORLD, "Hello, world!").]],
7864 [[io:format("~s~n", [?HELLO_WORLD])]])])
7874 -define(HELLO_WORLD, "Hello, world!").
7876 io:format("~s~n", [?HELLO_WORLD])
7880 @defmac AC_LANG_CALL (@var{prologue}, @var{function})
7882 Expands into a source file which consists of the @var{prologue}, and
7883 then a call to the @var{function} as body of the main function (e.g.,
7884 @code{main} in C). Since it uses @code{AC_LANG_PROGRAM}, the feature
7885 of the latter are available.
7887 This function will probably be replaced in the future by a version
7888 which would enable specifying the arguments. The use of this macro is
7889 not encouraged, as it violates strongly the typing system.
7891 This macro cannot be used for Erlang tests.
7894 @defmac AC_LANG_FUNC_LINK_TRY (@var{function})
7895 @acindex{LANG_FUNC_LINK_TRY}
7896 Expands into a source file which uses the @var{function} in the body of
7897 the main function (e.g., @code{main} in C). Since it uses
7898 @code{AC_LANG_PROGRAM}, the features of the latter are available.
7900 As @code{AC_LANG_CALL}, this macro is documented only for completeness.
7901 It is considered to be severely broken, and in the future will be
7902 removed in favor of actual function calls (with properly typed
7905 This macro cannot be used for Erlang tests.
7908 @node Running the Preprocessor
7909 @section Running the Preprocessor
7911 Sometimes one might need to run the preprocessor on some source file.
7912 @emph{Usually it is a bad idea}, as you typically need to @emph{compile}
7913 your project, not merely run the preprocessor on it; therefore you
7914 certainly want to run the compiler, not the preprocessor. Resist the
7915 temptation of following the easiest path.
7917 Nevertheless, if you need to run the preprocessor, then use
7918 @code{AC_PREPROC_IFELSE}.
7920 The macros described in this section cannot be used for tests in Erlang or
7921 Fortran, since those languages require no preprocessor.
7923 @defmac AC_PREPROC_IFELSE (@var{input}, @ovar{action-if-true}, @ovar{action-if-false})
7924 @acindex{PREPROC_IFELSE}
7925 Run the preprocessor of the current language (@pxref{Language Choice})
7926 on the @var{input}, run the shell commands @var{action-if-true} on
7927 success, @var{action-if-false} otherwise. The @var{input} can be made
7928 by @code{AC_LANG_PROGRAM} and friends.
7930 This macro uses @code{CPPFLAGS}, but not @code{CFLAGS}, because
7931 @option{-g}, @option{-O}, etc.@: are not valid options to many C
7934 It is customary to report unexpected failures with
7935 @code{AC_MSG_FAILURE}.
7941 AC_INIT([Hello], [1.0], [bug-hello@@example.org])
7942 AC_DEFINE([HELLO_WORLD], ["Hello, World\n"],
7943 [Greetings string.])
7945 [AC_LANG_PROGRAM([[const char hw[] = "Hello, World\n";]],
7946 [[fputs (hw, stdout);]])],
7947 [AC_MSG_RESULT([OK])],
7948 [AC_MSG_FAILURE([unexpected preprocessor failure])])
7955 checking for gcc... gcc
7956 checking for C compiler default output file name... a.out
7957 checking whether the C compiler works... yes
7958 checking whether we are cross compiling... no
7959 checking for suffix of executables...
7960 checking for suffix of object files... o
7961 checking whether we are using the GNU C compiler... yes
7962 checking whether gcc accepts -g... yes
7963 checking for gcc option to accept ISO C89... none needed
7964 checking how to run the C preprocessor... gcc -E
7970 The macro @code{AC_TRY_CPP} (@pxref{Obsolete Macros}) used to play the
7971 role of @code{AC_PREPROC_IFELSE}, but double quotes its argument, making
7972 it impossible to use it to elaborate sources. You are encouraged to
7973 get rid of your old use of the macro @code{AC_TRY_CPP} in favor of
7974 @code{AC_PREPROC_IFELSE}, but, in the first place, are you sure you need
7975 to run the @emph{preprocessor} and not the compiler?
7977 @defmac AC_EGREP_HEADER (@var{pattern}, @var{header-file}, @var{action-if-found}, @ovar{action-if-not-found})
7978 @acindex{EGREP_HEADER}
7979 If the output of running the preprocessor on the system header file
7980 @var{header-file} matches the extended regular expression
7981 @var{pattern}, execute shell commands @var{action-if-found}, otherwise
7982 execute @var{action-if-not-found}.
7985 @defmac AC_EGREP_CPP (@var{pattern}, @var{program}, @ovar{action-if-found}, @ovar{action-if-not-found})
7987 @var{program} is the text of a C or C++ program, on which shell
7988 variable, back quote, and backslash substitutions are performed. If the
7989 output of running the preprocessor on @var{program} matches the
7990 extended regular expression @var{pattern}, execute shell commands
7991 @var{action-if-found}, otherwise execute @var{action-if-not-found}.
7996 @node Running the Compiler
7997 @section Running the Compiler
7999 To check for a syntax feature of the current language's (@pxref{Language
8000 Choice}) compiler, such as whether it recognizes a certain keyword, or
8001 simply to try some library feature, use @code{AC_COMPILE_IFELSE} to try
8002 to compile a small program that uses that feature.
8004 @defmac AC_COMPILE_IFELSE (@var{input}, @ovar{action-if-true}, @ovar{action-if-false})
8005 @acindex{COMPILE_IFELSE}
8006 Run the compiler and compilation flags of the current language
8007 (@pxref{Language Choice}) on the @var{input}, run the shell commands
8008 @var{action-if-true} on success, @var{action-if-false} otherwise. The
8009 @var{input} can be made by @code{AC_LANG_PROGRAM} and friends.
8011 It is customary to report unexpected failures with
8012 @code{AC_MSG_FAILURE}. This macro does not try to link; use
8013 @code{AC_LINK_IFELSE} if you need to do that (@pxref{Running the
8018 For tests in Erlang, the @var{input} must be the source code of a module named
8019 @code{conftest}. @code{AC_COMPILE_IFELSE} generates a @file{conftest.beam}
8020 file that can be interpreted by the Erlang virtual machine (@code{ERL}). It is
8021 recommended to use @code{AC_LANG_PROGRAM} to specify the test program, to ensure
8022 that the Erlang module has the right name.
8024 @node Running the Linker
8025 @section Running the Linker
8027 To check for a library, a function, or a global variable, Autoconf
8028 @command{configure} scripts try to compile and link a small program that
8029 uses it. This is unlike Metaconfig, which by default uses @code{nm} or
8030 @code{ar} on the C library to try to figure out which functions are
8031 available. Trying to link with the function is usually a more reliable
8032 approach because it avoids dealing with the variations in the options
8033 and output formats of @code{nm} and @code{ar} and in the location of the
8034 standard libraries. It also allows configuring for cross-compilation or
8035 checking a function's runtime behavior if needed. On the other hand,
8036 it can be slower than scanning the libraries once, but accuracy is more
8037 important than speed.
8039 @code{AC_LINK_IFELSE} is used to compile test programs to test for
8040 functions and global variables. It is also used by @code{AC_CHECK_LIB}
8041 to check for libraries (@pxref{Libraries}), by adding the library being
8042 checked for to @code{LIBS} temporarily and trying to link a small
8046 @defmac AC_LINK_IFELSE (@var{input}, @ovar{action-if-true}, @ovar{action-if-false})
8047 @acindex{LINK_IFELSE}
8048 Run the compiler (and compilation flags) and the linker of the current
8049 language (@pxref{Language Choice}) on the @var{input}, run the shell
8050 commands @var{action-if-true} on success, @var{action-if-false}
8051 otherwise. The @var{input} can be made by @code{AC_LANG_PROGRAM} and
8054 @code{LDFLAGS} and @code{LIBS} are used for linking, in addition to the
8055 current compilation flags.
8057 It is customary to report unexpected failures with
8058 @code{AC_MSG_FAILURE}. This macro does not try to execute the program;
8059 use @code{AC_RUN_IFELSE} if you need to do that (@pxref{Runtime}).
8062 The @code{AC_LINK_IFELSE} macro cannot be used for Erlang tests, since Erlang
8063 programs are interpreted and do not require linking.
8068 @section Checking Runtime Behavior
8070 Sometimes you need to find out how a system performs at runtime, such
8071 as whether a given function has a certain capability or bug. If you
8072 can, make such checks when your program runs instead of when it is
8073 configured. You can check for things like the machine's endianness when
8074 your program initializes itself.
8076 If you really need to test for a runtime behavior while configuring,
8077 you can write a test program to determine the result, and compile and
8078 run it using @code{AC_RUN_IFELSE}. Avoid running test programs if
8079 possible, because this prevents people from configuring your package for
8082 @defmac AC_RUN_IFELSE (@var{input}, @ovar{action-if-true}, @ovar{action-if-false}, @ovar{action-if-cross-compiling})
8083 @acindex{RUN_IFELSE}
8084 If @var{program} compiles and links successfully and returns an exit
8085 status of 0 when executed, run shell commands @var{action-if-true}.
8086 Otherwise, run shell commands @var{action-if-false}.
8088 The @var{input} can be made by @code{AC_LANG_PROGRAM} and friends.
8089 @code{LDFLAGS} and @code{LIBS} are used for linking, in addition to the
8090 compilation flags of the current language (@pxref{Language Choice}).
8092 If the compiler being used does not produce executables that run on the
8093 system where @command{configure} is being run, then the test program is
8094 not run. If the optional shell commands @var{action-if-cross-compiling}
8095 are given, they are run instead. Otherwise, @command{configure} prints
8096 an error message and exits.
8098 In the @var{action-if-false} section, the failing exit status is
8099 available in the shell variable @samp{$?}. This exit status might be
8100 that of a failed compilation, or it might be that of a failed program
8103 It is customary to report unexpected failures with
8104 @code{AC_MSG_FAILURE}.
8107 Try to provide a pessimistic default value to use when cross-compiling
8108 makes runtime tests impossible. You do this by passing the optional
8109 last argument to @code{AC_RUN_IFELSE}. @command{autoconf} prints a
8110 warning message when creating @command{configure} each time it
8111 encounters a call to @code{AC_RUN_IFELSE} with no
8112 @var{action-if-cross-compiling} argument given. You may ignore the
8113 warning, though users cannot configure your package for
8114 cross-compiling. A few of the macros distributed with Autoconf produce
8115 this warning message.
8117 To configure for cross-compiling you can also choose a value for those
8118 parameters based on the canonical system name (@pxref{Manual
8119 Configuration}). Alternatively, set up a test results cache file with
8120 the correct values for the host system (@pxref{Caching Results}).
8122 @ovindex cross_compiling
8123 To provide a default for calls of @code{AC_RUN_IFELSE} that are embedded
8124 in other macros, including a few of the ones that come with Autoconf,
8125 you can test whether the shell variable @code{cross_compiling} is set to
8126 @samp{yes}, and then use an alternate method to get the results instead
8127 of calling the macros.
8129 A C or C++ runtime test should be portable.
8130 @xref{Portable C and C++}.
8132 Erlang tests must exit themselves the Erlang VM by calling the @code{halt/1}
8133 function: the given status code is used to determine the success of the test
8134 (status is @code{0}) or its failure (status is different than @code{0}), as
8135 explained above. It must be noted that data output through the standard output
8136 (e.g., using @code{io:format/2}) may be truncated when halting the VM.
8137 Therefore, if a test must output configuration information, it is recommended
8138 to create and to output data into the temporary file named @file{conftest.out},
8139 using the functions of module @code{file}. The @code{conftest.out} file is
8140 automatically deleted by the @code{AC_RUN_IFELSE} macro. For instance, a
8141 simplified implementation of Autoconf's @code{AC_ERLANG_SUBST_LIB_DIR} macro is:
8144 AC_INIT([LibdirTest], [1.0], [bug-libdirtest@@example.org])
8148 [AC_LANG_PROGRAM([], [dnl
8149 file:write_file("conftest.out", code:lib_dir()),
8151 [echo "code:lib_dir() returned: `cat conftest.out`"],
8152 [AC_MSG_FAILURE([test Erlang program execution failed])])
8157 @section Systemology
8160 This section aims at presenting some systems and pointers to
8161 documentation. It may help you addressing particular problems reported
8164 @uref{http://www.opengroup.org/susv3, Posix-conforming systems} are
8165 derived from the @uref{http://www.bell-labs.com/history/unix/, Unix
8168 The @uref{http://bhami.com/rosetta.html, Rosetta Stone for Unix}
8169 contains a table correlating the features of various Posix-conforming
8170 systems. @uref{http://www.levenez.com/unix/, Unix History} is a
8171 simplified diagram of how many Unix systems were derived from each
8174 @uref{http://heirloom.sourceforge.net/, The Heirloom Project}
8175 provides some variants of traditional implementations of Unix utilities.
8180 Darwin is also known as Mac OS X@. Beware that the file system @emph{can} be
8181 case-preserving, but case insensitive. This can cause nasty problems,
8182 since for instance the installation attempt for a package having an
8183 @file{INSTALL} file can result in @samp{make install} report that
8184 nothing was to be done!
8186 That's all dependent on whether the file system is a UFS (case
8187 sensitive) or HFS+ (case preserving). By default Apple wants you to
8188 install the OS on HFS+. Unfortunately, there are some pieces of
8189 software which really need to be built on UFS@. We may want to rebuild
8190 Darwin to have both UFS and HFS+ available (and put the /local/build
8193 @item @acronym{QNX} 4.25
8194 @cindex @acronym{QNX} 4.25
8195 @c FIXME: Please, if you feel like writing something more precise,
8196 @c it'd be great. In particular, I can't understand the difference with
8198 @acronym{QNX} is a realtime operating system running on Intel architecture
8199 meant to be scalable from the small embedded systems to the hundred
8200 processor super-computer. It claims to be Posix certified. More
8201 information is available on the
8202 @uref{http://www.qnx.com/, @acronym{QNX} home page}.
8206 @uref{http://h30097.www3.hp.com/@/docs/,
8207 Documentation of several versions of Tru64} is available in different
8210 @item Unix version 7
8211 @cindex Unix version 7
8213 Officially this was called the ``Seventh Edition'' of ``the @sc{unix}
8214 time-sharing system'' but we use the more-common name ``Unix version 7''.
8215 Documentation is available in the
8216 @uref{http://plan9.bell-labs.com/@/7thEdMan/, Unix Seventh Edition Manual}.
8217 Previous versions of Unix are called ``Unix version 6'', etc., but
8218 they were not as widely used.
8222 @node Multiple Cases
8223 @section Multiple Cases
8225 Some operations are accomplished in several possible ways, depending on
8226 the OS variant. Checking for them essentially requires a ``case
8227 statement''. Autoconf does not directly provide one; however, it is
8228 easy to simulate by using a shell variable to keep track of whether a
8229 way to perform the operation has been found yet.
8231 Here is an example that uses the shell variable @code{fstype} to keep
8232 track of whether the remaining cases need to be checked.
8236 AC_MSG_CHECKING([how to get file system type])
8238 # The order of these tests is important.
8239 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/statvfs.h>
8240 #include <sys/fstyp.h>]])],
8241 [AC_DEFINE([FSTYPE_STATVFS], [1],
8242 [Define if statvfs exists.])
8244 if test $fstype = no; then
8245 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/statfs.h>
8246 #include <sys/fstyp.h>]])],
8247 [AC_DEFINE([FSTYPE_USG_STATFS], [1],
8248 [Define if USG statfs.])
8251 if test $fstype = no; then
8252 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/statfs.h>
8253 #include <sys/vmount.h>]])]),
8254 [AC_DEFINE([FSTYPE_AIX_STATFS], [1],
8255 [Define if AIX statfs.])
8258 # (more cases omitted here)
8259 AC_MSG_RESULT([$fstype])
8263 @c ====================================================== Results of Tests.
8266 @chapter Results of Tests
8268 Once @command{configure} has determined whether a feature exists, what can
8269 it do to record that information? There are four sorts of things it can
8270 do: define a C preprocessor symbol, set a variable in the output files,
8271 save the result in a cache file for future @command{configure} runs, and
8272 print a message letting the user know the result of the test.
8275 * Defining Symbols:: Defining C preprocessor symbols
8276 * Setting Output Variables:: Replacing variables in output files
8277 * Special Chars in Variables:: Characters to beware of in variables
8278 * Caching Results:: Speeding up subsequent @command{configure} runs
8279 * Printing Messages:: Notifying @command{configure} users
8282 @node Defining Symbols
8283 @section Defining C Preprocessor Symbols
8285 A common action to take in response to a feature test is to define a C
8286 preprocessor symbol indicating the results of the test. That is done by
8287 calling @code{AC_DEFINE} or @code{AC_DEFINE_UNQUOTED}.
8289 By default, @code{AC_OUTPUT} places the symbols defined by these macros
8290 into the output variable @code{DEFS}, which contains an option
8291 @option{-D@var{symbol}=@var{value}} for each symbol defined. Unlike in
8292 Autoconf version 1, there is no variable @code{DEFS} defined while
8293 @command{configure} is running. To check whether Autoconf macros have
8294 already defined a certain C preprocessor symbol, test the value of the
8295 appropriate cache variable, as in this example:
8298 AC_CHECK_FUNC([vprintf], [AC_DEFINE([HAVE_VPRINTF], [1],
8299 [Define if vprintf exists.])])
8300 if test "$ac_cv_func_vprintf" != yes; then
8301 AC_CHECK_FUNC([_doprnt], [AC_DEFINE([HAVE_DOPRNT], [1],
8302 [Define if _doprnt exists.])])
8306 If @code{AC_CONFIG_HEADERS} has been called, then instead of creating
8307 @code{DEFS}, @code{AC_OUTPUT} creates a header file by substituting the
8308 correct values into @code{#define} statements in a template file.
8309 @xref{Configuration Headers}, for more information about this kind of
8312 @defmac AC_DEFINE (@var{variable}, @var{value}, @ovar{description})
8313 @defmacx AC_DEFINE (@var{variable})
8315 Define @var{variable} to @var{value} (verbatim), by defining a C
8316 preprocessor macro for @var{variable}. @var{variable} should be a C
8317 identifier, optionally suffixed by a parenthesized argument list to
8318 define a C preprocessor macro with arguments. The macro argument list,
8319 if present, should be a comma-separated list of C identifiers, possibly
8320 terminated by an ellipsis @samp{...} if C99 syntax is employed.
8321 @var{variable} should not contain comments, white space, trigraphs,
8322 backslash-newlines, universal character names, or non-@acronym{ASCII}
8325 @var{value} should not contain literal newlines, and if you are not
8326 using @code{AC_CONFIG_HEADERS} it should not contain any @samp{#}
8327 characters, as @command{make} tends to eat them. To use a shell variable,
8328 use @code{AC_DEFINE_UNQUOTED} instead.
8329 @var{description} is only useful if you are using
8330 @code{AC_CONFIG_HEADERS}. In this case, @var{description} is put into
8331 the generated @file{config.h.in} as the comment before the macro define.
8332 The following example defines the C preprocessor variable
8333 @code{EQUATION} to be the string constant @samp{"$a > $b"}:
8336 AC_DEFINE([EQUATION], ["$a > $b"],
8340 If neither @var{value} nor @var{description} are given, then
8341 @var{value} defaults to 1 instead of to the empty string. This is for
8342 backwards compatibility with older versions of Autoconf, but this usage
8343 is obsolescent and may be withdrawn in future versions of Autoconf.
8345 If the @var{variable} is a literal string, it is passed to
8346 @code{m4_pattern_allow} (@pxref{Forbidden Patterns}).
8348 If multiple @code{AC_DEFINE} statements are executed for the same
8349 @var{variable} name (not counting any parenthesized argument list),
8353 @defmac AC_DEFINE_UNQUOTED (@var{variable}, @var{value}, @ovar{description})
8354 @defmacx AC_DEFINE_UNQUOTED (@var{variable})
8355 @acindex{DEFINE_UNQUOTED}
8356 Like @code{AC_DEFINE}, but three shell expansions are
8357 performed---once---on @var{variable} and @var{value}: variable expansion
8358 (@samp{$}), command substitution (@samp{`}), and backslash escaping
8359 (@samp{\}). Single and double quote characters in the value have no
8360 special meaning. Use this macro instead of @code{AC_DEFINE} when
8361 @var{variable} or @var{value} is a shell variable. Examples:
8364 AC_DEFINE_UNQUOTED([config_machfile], ["$machfile"],
8365 [Configuration machine file.])
8366 AC_DEFINE_UNQUOTED([GETGROUPS_T], [$ac_cv_type_getgroups],
8367 [getgroups return type.])
8368 AC_DEFINE_UNQUOTED([$ac_tr_hdr], [1],
8369 [Translated header name.])
8373 Due to a syntactical bizarreness of the Bourne shell, do not use
8374 semicolons to separate @code{AC_DEFINE} or @code{AC_DEFINE_UNQUOTED}
8375 calls from other macro calls or shell code; that can cause syntax errors
8376 in the resulting @command{configure} script. Use either blanks or
8377 newlines. That is, do this:
8380 AC_CHECK_HEADER([elf.h],
8381 [AC_DEFINE([SVR4], [1], [System V Release 4]) LIBS="-lelf $LIBS"])
8388 AC_CHECK_HEADER([elf.h],
8389 [AC_DEFINE([SVR4], [1], [System V Release 4])
8390 LIBS="-lelf $LIBS"])
8397 AC_CHECK_HEADER([elf.h],
8398 [AC_DEFINE([SVR4], [1], [System V Release 4]); LIBS="-lelf $LIBS"])
8401 @node Setting Output Variables
8402 @section Setting Output Variables
8403 @cindex Output variables
8405 Another way to record the results of tests is to set @dfn{output
8406 variables}, which are shell variables whose values are substituted into
8407 files that @command{configure} outputs. The two macros below create new
8408 output variables. @xref{Preset Output Variables}, for a list of output
8409 variables that are always available.
8411 @defmac AC_SUBST (@var{variable}, @ovar{value})
8413 Create an output variable from a shell variable. Make @code{AC_OUTPUT}
8414 substitute the variable @var{variable} into output files (typically one
8415 or more makefiles). This means that @code{AC_OUTPUT}
8416 replaces instances of @samp{@@@var{variable}@@} in input files with the
8417 value that the shell variable @var{variable} has when @code{AC_OUTPUT}
8418 is called. The value can contain any non-@code{NUL} character, including
8420 Variable occurrences should not overlap: e.g., an input file should
8421 not contain @samp{@@@var{var1}@@@var{var2}@@} if @var{var1} and @var{var2}
8423 The substituted value is not rescanned for more output variables;
8424 occurrences of @samp{@@@var{variable}@@} in the value are inserted
8425 literally into the output file. (The algorithm uses the special marker
8426 @code{|#_!!_#|} internally, so neither the substituted value nor the
8427 output file may contain @code{|#_!!_#|}.)
8429 If @var{value} is given, in addition assign it to @var{variable}.
8431 The string @var{variable} is passed to @code{m4_pattern_allow}
8432 (@pxref{Forbidden Patterns}).
8435 @defmac AC_SUBST_FILE (@var{variable})
8436 @acindex{SUBST_FILE}
8437 Another way to create an output variable from a shell variable. Make
8438 @code{AC_OUTPUT} insert (without substitutions) the contents of the file
8439 named by shell variable @var{variable} into output files. This means
8440 that @code{AC_OUTPUT} replaces instances of
8441 @samp{@@@var{variable}@@} in output files (such as @file{Makefile.in})
8442 with the contents of the file that the shell variable @var{variable}
8443 names when @code{AC_OUTPUT} is called. Set the variable to
8444 @file{/dev/null} for cases that do not have a file to insert.
8445 This substitution occurs only when the @samp{@@@var{variable}@@} is on a
8446 line by itself, optionally surrounded by spaces and tabs. The
8447 substitution replaces the whole line, including the spaces, tabs, and
8448 the terminating newline.
8450 This macro is useful for inserting makefile fragments containing
8451 special dependencies or other @code{make} directives for particular host
8452 or target types into makefiles. For example, @file{configure.ac}
8456 AC_SUBST_FILE([host_frag])
8457 host_frag=$srcdir/conf/sun4.mh
8461 and then a @file{Makefile.in} could contain:
8467 The string @var{variable} is passed to @code{m4_pattern_allow}
8468 (@pxref{Forbidden Patterns}).
8471 @cindex Precious Variable
8472 @cindex Variable, Precious
8473 Running @command{configure} in varying environments can be extremely
8474 dangerous. If for instance the user runs @samp{CC=bizarre-cc
8475 ./configure}, then the cache, @file{config.h}, and many other output
8476 files depend upon @command{bizarre-cc} being the C compiler. If
8477 for some reason the user runs @command{./configure} again, or if it is
8478 run via @samp{./config.status --recheck}, (@xref{Automatic Remaking},
8479 and @pxref{config.status Invocation}), then the configuration can be
8480 inconsistent, composed of results depending upon two different
8483 Environment variables that affect this situation, such as @samp{CC}
8484 above, are called @dfn{precious variables}, and can be declared as such
8485 by @code{AC_ARG_VAR}.
8487 @defmac AC_ARG_VAR (@var{variable}, @var{description})
8489 Declare @var{variable} is a precious variable, and include its
8490 @var{description} in the variable section of @samp{./configure --help}.
8492 Being precious means that
8495 @var{variable} is substituted via @code{AC_SUBST}.
8498 The value of @var{variable} when @command{configure} was launched is
8499 saved in the cache, including if it was not specified on the command
8500 line but via the environment. Indeed, while @command{configure} can
8501 notice the definition of @code{CC} in @samp{./configure CC=bizarre-cc},
8502 it is impossible to notice it in @samp{CC=bizarre-cc ./configure},
8503 which, unfortunately, is what most users do.
8505 We emphasize that it is the @emph{initial} value of @var{variable} which
8506 is saved, not that found during the execution of @command{configure}.
8507 Indeed, specifying @samp{./configure FOO=foo} and letting
8508 @samp{./configure} guess that @code{FOO} is @code{foo} can be two
8512 @var{variable} is checked for consistency between two
8513 @command{configure} runs. For instance:
8516 $ @kbd{./configure --silent --config-cache}
8517 $ @kbd{CC=cc ./configure --silent --config-cache}
8518 configure: error: `CC' was not set in the previous run
8519 configure: error: changes in the environment can compromise \
8521 configure: error: run `make distclean' and/or \
8522 `rm config.cache' and start over
8526 and similarly if the variable is unset, or if its content is changed.
8530 @var{variable} is kept during automatic reconfiguration
8531 (@pxref{config.status Invocation}) as if it had been passed as a command
8532 line argument, including when no cache is used:
8535 $ @kbd{CC=/usr/bin/cc ./configure undeclared_var=raboof --silent}
8536 $ @kbd{./config.status --recheck}
8537 running CONFIG_SHELL=/bin/sh /bin/sh ./configure undeclared_var=raboof \
8538 CC=/usr/bin/cc --no-create --no-recursion
8543 @node Special Chars in Variables
8544 @section Special Characters in Output Variables
8545 @cindex Output variables, special characters in
8547 Many output variables are intended to be evaluated both by
8548 @command{make} and by the shell. Some characters are expanded
8549 differently in these two contexts, so to avoid confusion these
8550 variables' values should not contain any of the following characters:
8553 " # $ & ' ( ) * ; < > ? [ \ ^ ` |
8556 Also, these variables' values should neither contain newlines, nor start
8557 with @samp{~}, nor contain white space or @samp{:} immediately followed
8558 by @samp{~}. The values can contain nonempty sequences of white space
8559 characters like tabs and spaces, but each such sequence might
8560 arbitrarily be replaced by a single space during substitution.
8562 These restrictions apply both to the values that @command{configure}
8563 computes, and to the values set directly by the user. For example, the
8564 following invocations of @command{configure} are problematic, since they
8565 attempt to use special characters within @code{CPPFLAGS} and white space
8566 within @code{$(srcdir)}:
8569 CPPFLAGS='-DOUCH="&\"#$*?"' '../My Source/ouch-1.0/configure'
8571 '../My Source/ouch-1.0/configure' CPPFLAGS='-DOUCH="&\"#$*?"'
8574 @node Caching Results
8575 @section Caching Results
8578 To avoid checking for the same features repeatedly in various
8579 @command{configure} scripts (or in repeated runs of one script),
8580 @command{configure} can optionally save the results of many checks in a
8581 @dfn{cache file} (@pxref{Cache Files}). If a @command{configure} script
8582 runs with caching enabled and finds a cache file, it reads the results
8583 of previous runs from the cache and avoids rerunning those checks. As a
8584 result, @command{configure} can then run much faster than if it had to
8585 perform all of the checks every time.
8587 @defmac AC_CACHE_VAL (@var{cache-id}, @var{commands-to-set-it})
8589 Ensure that the results of the check identified by @var{cache-id} are
8590 available. If the results of the check were in the cache file that was
8591 read, and @command{configure} was not given the @option{--quiet} or
8592 @option{--silent} option, print a message saying that the result was
8593 cached; otherwise, run the shell commands @var{commands-to-set-it}. If
8594 the shell commands are run to determine the value, the value is
8595 saved in the cache file just before @command{configure} creates its output
8596 files. @xref{Cache Variable Names}, for how to choose the name of the
8597 @var{cache-id} variable.
8599 The @var{commands-to-set-it} @emph{must have no side effects} except for
8600 setting the variable @var{cache-id}, see below.
8603 @defmac AC_CACHE_CHECK (@var{message}, @var{cache-id}, @var{commands-to-set-it})
8604 @acindex{CACHE_CHECK}
8605 A wrapper for @code{AC_CACHE_VAL} that takes care of printing the
8606 messages. This macro provides a convenient shorthand for the most
8607 common way to use these macros. It calls @code{AC_MSG_CHECKING} for
8608 @var{message}, then @code{AC_CACHE_VAL} with the @var{cache-id} and
8609 @var{commands} arguments, and @code{AC_MSG_RESULT} with @var{cache-id}.
8611 The @var{commands-to-set-it} @emph{must have no side effects} except for
8612 setting the variable @var{cache-id}, see below.
8615 It is common to find buggy macros using @code{AC_CACHE_VAL} or
8616 @code{AC_CACHE_CHECK}, because people are tempted to call
8617 @code{AC_DEFINE} in the @var{commands-to-set-it}. Instead, the code that
8618 @emph{follows} the call to @code{AC_CACHE_VAL} should call
8619 @code{AC_DEFINE}, by examining the value of the cache variable. For
8620 instance, the following macro is broken:
8624 AC_DEFUN([AC_SHELL_TRUE],
8625 [AC_CACHE_CHECK([whether true(1) works], [my_cv_shell_true_works],
8626 [my_cv_shell_true_works=no
8627 (true) 2>/dev/null && my_cv_shell_true_works=yes
8628 if test "$my_cv_shell_true_works" = yes; then
8629 AC_DEFINE([TRUE_WORKS], [1],
8630 [Define if `true(1)' works properly.])
8637 This fails if the cache is enabled: the second time this macro is run,
8638 @code{TRUE_WORKS} @emph{will not be defined}. The proper implementation
8643 AC_DEFUN([AC_SHELL_TRUE],
8644 [AC_CACHE_CHECK([whether true(1) works], [my_cv_shell_true_works],
8645 [my_cv_shell_true_works=no
8646 (true) 2>/dev/null && my_cv_shell_true_works=yes])
8647 if test "$my_cv_shell_true_works" = yes; then
8648 AC_DEFINE([TRUE_WORKS], [1],
8649 [Define if `true(1)' works properly.])
8655 Also, @var{commands-to-set-it} should not print any messages, for
8656 example with @code{AC_MSG_CHECKING}; do that before calling
8657 @code{AC_CACHE_VAL}, so the messages are printed regardless of whether
8658 the results of the check are retrieved from the cache or determined by
8659 running the shell commands.
8662 * Cache Variable Names:: Shell variables used in caches
8663 * Cache Files:: Files @command{configure} uses for caching
8664 * Cache Checkpointing:: Loading and saving the cache file
8667 @node Cache Variable Names
8668 @subsection Cache Variable Names
8669 @cindex Cache variable
8671 The names of cache variables should have the following format:
8674 @var{package-prefix}_cv_@var{value-type}_@var{specific-value}_@ovar{additional-options}
8678 for example, @samp{ac_cv_header_stat_broken} or
8679 @samp{ac_cv_prog_gcc_traditional}. The parts of the variable name are:
8682 @item @var{package-prefix}
8683 An abbreviation for your package or organization; the same prefix you
8684 begin local Autoconf macros with, except lowercase by convention.
8685 For cache values used by the distributed Autoconf macros, this value is
8689 Indicates that this shell variable is a cache value. This string
8690 @emph{must} be present in the variable name, including the leading
8693 @item @var{value-type}
8694 A convention for classifying cache values, to produce a rational naming
8695 system. The values used in Autoconf are listed in @ref{Macro Names}.
8697 @item @var{specific-value}
8698 Which member of the class of cache values this test applies to.
8699 For example, which function (@samp{alloca}), program (@samp{gcc}), or
8700 output variable (@samp{INSTALL}).
8702 @item @var{additional-options}
8703 Any particular behavior of the specific member that this test applies to.
8704 For example, @samp{broken} or @samp{set}. This part of the name may
8705 be omitted if it does not apply.
8708 The values assigned to cache variables may not contain newlines.
8709 Usually, their values are Boolean (@samp{yes} or @samp{no}) or the
8710 names of files or functions; so this is not an important restriction.
8713 @subsection Cache Files
8715 A cache file is a shell script that caches the results of configure
8716 tests run on one system so they can be shared between configure scripts
8717 and configure runs. It is not useful on other systems. If its contents
8718 are invalid for some reason, the user may delete or edit it.
8720 By default, @command{configure} uses no cache file,
8721 to avoid problems caused by accidental
8722 use of stale cache files.
8724 To enable caching, @command{configure} accepts @option{--config-cache} (or
8725 @option{-C}) to cache results in the file @file{config.cache}.
8726 Alternatively, @option{--cache-file=@var{file}} specifies that
8727 @var{file} be the cache file. The cache file is created if it does not
8728 exist already. When @command{configure} calls @command{configure} scripts in
8729 subdirectories, it uses the @option{--cache-file} argument so that they
8730 share the same cache. @xref{Subdirectories}, for information on
8731 configuring subdirectories with the @code{AC_CONFIG_SUBDIRS} macro.
8733 @file{config.status} only pays attention to the cache file if it is
8734 given the @option{--recheck} option, which makes it rerun
8735 @command{configure}.
8737 It is wrong to try to distribute cache files for particular system types.
8738 There is too much room for error in doing that, and too much
8739 administrative overhead in maintaining them. For any features that
8740 can't be guessed automatically, use the standard method of the canonical
8741 system type and linking files (@pxref{Manual Configuration}).
8743 The site initialization script can specify a site-wide cache file to
8744 use, instead of the usual per-program cache. In this case, the cache
8745 file gradually accumulates information whenever someone runs a new
8746 @command{configure} script. (Running @command{configure} merges the new cache
8747 results with the existing cache file.) This may cause problems,
8748 however, if the system configuration (e.g., the installed libraries or
8749 compilers) changes and the stale cache file is not deleted.
8751 @node Cache Checkpointing
8752 @subsection Cache Checkpointing
8754 If your configure script, or a macro called from @file{configure.ac}, happens
8755 to abort the configure process, it may be useful to checkpoint the cache
8756 a few times at key points using @code{AC_CACHE_SAVE}. Doing so
8757 reduces the amount of time it takes to rerun the configure script with
8758 (hopefully) the error that caused the previous abort corrected.
8760 @c FIXME: Do we really want to document this guy?
8761 @defmac AC_CACHE_LOAD
8762 @acindex{CACHE_LOAD}
8763 Loads values from existing cache file, or creates a new cache file if a
8764 cache file is not found. Called automatically from @code{AC_INIT}.
8767 @defmac AC_CACHE_SAVE
8768 @acindex{CACHE_SAVE}
8769 Flushes all cached values to the cache file. Called automatically from
8770 @code{AC_OUTPUT}, but it can be quite useful to call
8771 @code{AC_CACHE_SAVE} at key points in @file{configure.ac}.
8777 @r{ @dots{} AC_INIT, etc. @dots{}}
8779 # Checks for programs.
8782 @r{ @dots{} more program checks @dots{}}
8787 # Checks for libraries.
8788 AC_CHECK_LIB([nsl], [gethostbyname])
8789 AC_CHECK_LIB([socket], [connect])
8790 @r{ @dots{} more lib checks @dots{}}
8795 # Might abort@dots{}
8796 AM_PATH_GTK([1.0.2], [], [AC_MSG_ERROR([GTK not in path])])
8797 AM_PATH_GTKMM([0.9.5], [], [AC_MSG_ERROR([GTK not in path])])
8799 @r{ @dots{} AC_OUTPUT, etc. @dots{}}
8802 @node Printing Messages
8803 @section Printing Messages
8804 @cindex Messages, from @command{configure}
8806 @command{configure} scripts need to give users running them several kinds
8807 of information. The following macros print messages in ways appropriate
8808 for each kind. The arguments to all of them get enclosed in shell
8809 double quotes, so the shell performs variable and back-quote
8810 substitution on them.
8812 These macros are all wrappers around the @command{echo} shell command.
8813 They direct output to the appropriate file descriptor (@pxref{File
8814 Descriptor Macros}).
8815 @command{configure} scripts should rarely need to run @command{echo} directly
8816 to print messages for the user. Using these macros makes it easy to
8817 change how and when each kind of message is printed; such changes need
8818 only be made to the macro definitions and all the callers change
8821 To diagnose static issues, i.e., when @command{autoconf} is run, see
8822 @ref{Reporting Messages}.
8824 @defmac AC_MSG_CHECKING (@var{feature-description})
8825 @acindex{MSG_CHECKING}
8826 Notify the user that @command{configure} is checking for a particular
8827 feature. This macro prints a message that starts with @samp{checking }
8828 and ends with @samp{...} and no newline. It must be followed by a call
8829 to @code{AC_MSG_RESULT} to print the result of the check and the
8830 newline. The @var{feature-description} should be something like
8831 @samp{whether the Fortran compiler accepts C++ comments} or @samp{for
8834 This macro prints nothing if @command{configure} is run with the
8835 @option{--quiet} or @option{--silent} option.
8838 @defmac AC_MSG_RESULT (@var{result-description})
8839 @acindex{MSG_RESULT}
8840 Notify the user of the results of a check. @var{result-description} is
8841 almost always the value of the cache variable for the check, typically
8842 @samp{yes}, @samp{no}, or a file name. This macro should follow a call
8843 to @code{AC_MSG_CHECKING}, and the @var{result-description} should be
8844 the completion of the message printed by the call to
8845 @code{AC_MSG_CHECKING}.
8847 This macro prints nothing if @command{configure} is run with the
8848 @option{--quiet} or @option{--silent} option.
8851 @defmac AC_MSG_NOTICE (@var{message})
8852 @acindex{MSG_NOTICE}
8853 Deliver the @var{message} to the user. It is useful mainly to print a
8854 general description of the overall purpose of a group of feature checks,
8858 AC_MSG_NOTICE([checking if stack overflow is detectable])
8861 This macro prints nothing if @command{configure} is run with the
8862 @option{--quiet} or @option{--silent} option.
8865 @defmac AC_MSG_ERROR (@var{error-description}, @ovar{exit-status})
8867 Notify the user of an error that prevents @command{configure} from
8868 completing. This macro prints an error message to the standard error
8869 output and exits @command{configure} with @var{exit-status} (1 by default).
8870 @var{error-description} should be something like @samp{invalid value
8873 The @var{error-description} should start with a lower-case letter, and
8874 ``cannot'' is preferred to ``can't''.
8877 @defmac AC_MSG_FAILURE (@var{error-description}, @ovar{exit-status})
8878 @acindex{MSG_FAILURE}
8879 This @code{AC_MSG_ERROR} wrapper notifies the user of an error that
8880 prevents @command{configure} from completing @emph{and} that additional
8881 details are provided in @file{config.log}. This is typically used when
8882 abnormal results are found during a compilation.
8885 @defmac AC_MSG_WARN (@var{problem-description})
8887 Notify the @command{configure} user of a possible problem. This macro
8888 prints the message to the standard error output; @command{configure}
8889 continues running afterward, so macros that call @code{AC_MSG_WARN} should
8890 provide a default (back-up) behavior for the situations they warn about.
8891 @var{problem-description} should be something like @samp{ln -s seems to
8897 @c ====================================================== Programming in M4.
8899 @node Programming in M4
8900 @chapter Programming in M4
8903 Autoconf is written on top of two layers: @dfn{M4sugar}, which provides
8904 convenient macros for pure M4 programming, and @dfn{M4sh}, which
8905 provides macros dedicated to shell script generation.
8907 As of this version of Autoconf, these two layers are still experimental,
8908 and their interface might change in the future. As a matter of fact,
8909 @emph{anything that is not documented must not be used}.
8912 * M4 Quotation:: Protecting macros from unwanted expansion
8913 * Using autom4te:: The Autoconf executables backbone
8914 * Programming in M4sugar:: Convenient pure M4 macros
8915 * Programming in M4sh:: Common shell Constructs
8916 * File Descriptor Macros:: File descriptor macros for input and output
8920 @section M4 Quotation
8921 @cindex M4 quotation
8924 @c FIXME: Grmph, yet another quoting myth: quotation has *never*
8925 @c prevented `expansion' of $1. Unless it refers to the expansion
8926 @c of the value of $1? Anyway, we need a rewrite here@enddots{}
8928 The most common problem with existing macros is an improper quotation.
8929 This section, which users of Autoconf can skip, but which macro writers
8930 @emph{must} read, first justifies the quotation scheme that was chosen
8931 for Autoconf and then ends with a rule of thumb. Understanding the
8932 former helps one to follow the latter.
8935 * Active Characters:: Characters that change the behavior of M4
8936 * One Macro Call:: Quotation and one macro call
8937 * Quotation and Nested Macros:: Macros calling macros
8938 * Changequote is Evil:: Worse than INTERCAL: M4 + changequote
8939 * Quadrigraphs:: Another way to escape special characters
8940 * Quotation Rule Of Thumb:: One parenthesis, one quote
8943 @node Active Characters
8944 @subsection Active Characters
8946 To fully understand where proper quotation is important, you first need
8947 to know what the special characters are in Autoconf: @samp{#} introduces
8948 a comment inside which no macro expansion is performed, @samp{,}
8949 separates arguments, @samp{[} and @samp{]} are the quotes themselves,
8950 and finally @samp{(} and @samp{)} (which M4 tries to match by
8953 In order to understand the delicate case of macro calls, we first have
8954 to present some obvious failures. Below they are ``obvious-ified'',
8955 but when you find them in real life, they are usually in disguise.
8957 Comments, introduced by a hash and running up to the newline, are opaque
8958 tokens to the top level: active characters are turned off, and there is
8962 # define([def], ine)
8963 @result{}# define([def], ine)
8966 Each time there can be a macro expansion, there is a quotation
8967 expansion, i.e., one level of quotes is stripped:
8973 @result{}int tab[10];
8976 Without this in mind, the reader might try hopelessly to use her macro
8980 define([array], [int tab[10];])
8988 How can you correctly output the intended results@footnote{Using
8992 @node One Macro Call
8993 @subsection One Macro Call
8995 Let's proceed on the interaction between active characters and macros
8996 with this small macro, which just returns its first argument:
9003 The two pairs of quotes above are not part of the arguments of
9004 @code{define}; rather, they are understood by the top level when it
9005 tries to find the arguments of @code{define}. Therefore, assuming
9006 @code{car} is not already defined, it is equivalent to write:
9013 But, while it is acceptable for a @file{configure.ac} to avoid unnecessary
9014 quotes, it is bad practice for Autoconf macros which must both be more
9015 robust and also advocate perfect style.
9017 At the top level, there are only two possibilities: either you
9023 [car(foo, bar, baz)]
9024 @result{}car(foo, bar, baz)
9027 Let's pay attention to the special characters:
9031 @error{}EOF in argument list
9034 The closing parenthesis is hidden in the comment; with a hypothetical
9035 quoting, the top level understood it this way:
9042 Proper quotation, of course, fixes the problem:
9049 Here are more examples:
9072 With this in mind, we can explore the cases where macros invoke
9076 @node Quotation and Nested Macros
9077 @subsection Quotation and Nested Macros
9079 The examples below use the following macros:
9083 define([active], [ACT, IVE])
9084 define([array], [int tab[10]])
9087 Each additional embedded macro call introduces other possible
9088 interesting quotations:
9099 In the first case, the top level looks for the arguments of @code{car},
9100 and finds @samp{active}. Because M4 evaluates its arguments
9101 before applying the macro, @samp{active} is expanded, which results in:
9109 In the second case, the top level gives @samp{active} as first and only
9110 argument of @code{car}, which results in:
9118 i.e., the argument is evaluated @emph{after} the macro that invokes it.
9119 In the third case, @code{car} receives @samp{[active]}, which results in:
9127 exactly as we already saw above.
9129 The example above, applied to a more realistic example, gives:
9136 car([[int tab[10];]])
9137 @result{}int tab[10];
9141 Huh? The first case is easily understood, but why is the second wrong,
9142 and the third right? To understand that, you must know that after
9143 M4 expands a macro, the resulting text is immediately subjected
9144 to macro expansion and quote removal. This means that the quote removal
9145 occurs twice---first before the argument is passed to the @code{car}
9146 macro, and second after the @code{car} macro expands to the first
9149 As the author of the Autoconf macro @code{car}, you then consider it to
9150 be incorrect that your users have to double-quote the arguments of
9151 @code{car}, so you ``fix'' your macro. Let's call it @code{qar} for
9155 define([qar], [[$1]])
9159 and check that @code{qar} is properly fixed:
9163 @result{}int tab[10];
9167 Ahhh! That's much better.
9169 But note what you've done: now that the arguments are literal strings,
9170 if the user wants to use the results of expansions as arguments, she has
9171 to use an @emph{unquoted} macro call:
9179 where she wanted to reproduce what she used to do with @code{car}:
9187 Worse yet: she wants to use a macro that produces a set of @code{cpp}
9191 define([my_includes], [#include <stdio.h>])
9193 @result{}#include <stdio.h>
9195 @error{}EOF in argument list
9198 This macro, @code{qar}, because it double quotes its arguments, forces
9199 its users to leave their macro calls unquoted, which is dangerous.
9200 Commas and other active symbols are interpreted by M4 before
9201 they are given to the macro, often not in the way the users expect.
9202 Also, because @code{qar} behaves differently from the other macros,
9203 it's an exception that should be avoided in Autoconf.
9205 @node Changequote is Evil
9206 @subsection @code{changequote} is Evil
9207 @cindex @code{changequote}
9209 The temptation is often high to bypass proper quotation, in particular
9210 when it's late at night. Then, many experienced Autoconf hackers
9211 finally surrender to the dark side of the force and use the ultimate
9212 weapon: @code{changequote}.
9214 The M4 builtin @code{changequote} belongs to a set of primitives that
9215 allow one to adjust the syntax of the language to adjust it to one's
9216 needs. For instance, by default M4 uses @samp{`} and @samp{'} as
9217 quotes, but in the context of shell programming (and actually of most
9218 programming languages), that's about the worst choice one can make:
9219 because of strings and back-quoted expressions in shell code (such as
9220 @samp{'this'} and @samp{`that`}), because of literal characters in usual
9221 programming languages (as in @samp{'0'}), there are many unbalanced
9222 @samp{`} and @samp{'}. Proper M4 quotation then becomes a nightmare, if
9223 not impossible. In order to make M4 useful in such a context, its
9224 designers have equipped it with @code{changequote}, which makes it
9225 possible to choose another pair of quotes. M4sugar, M4sh, Autoconf, and
9226 Autotest all have chosen to use @samp{[} and @samp{]}. Not especially
9227 because they are unlikely characters, but @emph{because they are
9228 characters unlikely to be unbalanced}.
9230 There are other magic primitives, such as @code{changecom} to specify
9231 what syntactic forms are comments (it is common to see
9232 @samp{changecom(<!--, -->)} when M4 is used to produce HTML pages),
9233 @code{changeword} and @code{changesyntax} to change other syntactic
9234 details (such as the character to denote the @var{n}th argument, @samp{$} by
9235 default, the parenthesis around arguments, etc.).
9237 These primitives are really meant to make M4 more useful for specific
9238 domains: they should be considered like command line options:
9239 @option{--quotes}, @option{--comments}, @option{--words}, and
9240 @option{--syntax}. Nevertheless, they are implemented as M4 builtins, as
9241 it makes M4 libraries self contained (no need for additional options).
9243 There lies the problem@enddots{}
9247 The problem is that it is then tempting to use them in the middle of an
9248 M4 script, as opposed to its initialization. This, if not carefully
9249 thought out, can lead to disastrous effects: @emph{you are changing the
9250 language in the middle of the execution}. Changing and restoring the
9251 syntax is often not enough: if you happened to invoke macros in between,
9252 these macros are lost, as the current syntax is probably not
9253 the one they were implemented with.
9255 @c FIXME: I've been looking for a short, real case example, but I
9260 @subsection Quadrigraphs
9261 @cindex quadrigraphs
9262 @cindex @samp{@@S|@@}
9263 @cindex @samp{@@&t@@}
9264 @c Info cannot handle `:' in index entries.
9265 @c @cindex @samp{@@<:@@}
9266 @c @cindex @samp{@@:>@@}
9267 @c @cindex @samp{@@%:@@}
9269 When writing an Autoconf macro you may occasionally need to generate
9270 special characters that are difficult to express with the standard
9271 Autoconf quoting rules. For example, you may need to output the regular
9272 expression @samp{[^[]}, which matches any character other than @samp{[}.
9273 This expression contains unbalanced brackets so it cannot be put easily
9276 You can work around this problem by using one of the following
9292 Quadrigraphs are replaced at a late stage of the translation process,
9293 after @command{m4} is run, so they do not get in the way of M4 quoting.
9294 For example, the string @samp{^@@<:@@}, independently of its quotation,
9295 appears as @samp{^[} in the output.
9297 The empty quadrigraph can be used:
9300 @item to mark trailing spaces explicitly
9302 Trailing spaces are smashed by @command{autom4te}. This is a feature.
9304 @item to produce other quadrigraphs
9306 For instance @samp{@@<@@&t@@:@@} produces @samp{@@<:@@}.
9308 @item to escape @emph{occurrences} of forbidden patterns
9310 For instance you might want to mention @code{AC_FOO} in a comment, while
9311 still being sure that @command{autom4te} still catches unexpanded
9312 @samp{AC_*}. Then write @samp{AC@@&t@@_FOO}.
9315 The name @samp{@@&t@@} was suggested by Paul Eggert:
9318 I should give some credit to the @samp{@@&t@@} pun. The @samp{&} is my
9319 own invention, but the @samp{t} came from the source code of the
9320 @sc{algol68c} compiler, written by Steve Bourne (of Bourne shell fame),
9321 and which used @samp{mt} to denote the empty string. In C, it would
9322 have looked like something like:
9325 char const mt[] = "";
9329 but of course the source code was written in Algol 68.
9331 I don't know where he got @samp{mt} from: it could have been his own
9332 invention, and I suppose it could have been a common pun around the
9333 Cambridge University computer lab at the time.
9336 @node Quotation Rule Of Thumb
9337 @subsection Quotation Rule Of Thumb
9339 To conclude, the quotation rule of thumb is:
9341 @center @emph{One pair of quotes per pair of parentheses.}
9343 Never over-quote, never under-quote, in particular in the definition of
9344 macros. In the few places where the macros need to use brackets
9345 (usually in C program text or regular expressions), properly quote
9346 @emph{the arguments}!
9348 It is common to read Autoconf programs with snippets like:
9352 changequote(<<, >>)dnl
9354 #ifndef tzname /* For SGI. */
9355 extern char *tzname[]; /* RS6000 and others reject char **tzname. */
9357 changequote([, ])dnl
9358 [atoi (*tzname);], ac_cv_var_tzname=yes, ac_cv_var_tzname=no)
9362 which is incredibly useless since @code{AC_TRY_LINK} is @emph{already}
9363 double quoting, so you just need:
9368 #ifndef tzname /* For SGI. */
9369 extern char *tzname[]; /* RS6000 and others reject char **tzname. */
9372 [ac_cv_var_tzname=yes],
9373 [ac_cv_var_tzname=no])
9377 The M4-fluent reader might note that these two examples are rigorously
9378 equivalent, since M4 swallows both the @samp{changequote(<<, >>)}
9379 and @samp{<<} @samp{>>} when it @dfn{collects} the arguments: these
9380 quotes are not part of the arguments!
9382 Simplified, the example above is just doing this:
9385 changequote(<<, >>)dnl
9387 changequote([, ])dnl
9397 With macros that do not double quote their arguments (which is the
9398 rule), double-quote the (risky) literals:
9401 AC_LINK_IFELSE([AC_LANG_PROGRAM(
9403 #ifndef tzname /* For SGI. */
9404 extern char *tzname[]; /* RS6000 and others reject char **tzname. */
9406 [atoi (*tzname);])],
9407 [ac_cv_var_tzname=yes],
9408 [ac_cv_var_tzname=no])
9411 Please note that the macro @code{AC_TRY_LINK} is obsolete, so you really
9412 should be using @code{AC_LINK_IFELSE} instead.
9414 @xref{Quadrigraphs}, for what to do if you run into a hopeless case
9415 where quoting does not suffice.
9417 When you create a @command{configure} script using newly written macros,
9418 examine it carefully to check whether you need to add more quotes in
9419 your macros. If one or more words have disappeared in the M4
9420 output, you need more quotes. When in doubt, quote.
9422 However, it's also possible to put on too many layers of quotes. If
9423 this happens, the resulting @command{configure} script may contain
9424 unexpanded macros. The @command{autoconf} program checks for this problem
9425 by looking for the string @samp{AC_} in @file{configure}. However, this
9426 heuristic does not work in general: for example, it does not catch
9427 overquoting in @code{AC_DEFINE} descriptions.
9430 @c ---------------------------------------- Using autom4te
9432 @node Using autom4te
9433 @section Using @command{autom4te}
9435 The Autoconf suite, including M4sugar, M4sh, and Autotest, in addition
9436 to Autoconf per se, heavily rely on M4. All these different uses
9437 revealed common needs factored into a layer over M4:
9438 @command{autom4te}@footnote{
9440 Yet another great name from Lars J. Aas.
9444 @command{autom4te} is a preprocessor that is like @command{m4}.
9445 It supports M4 extensions designed for use in tools like Autoconf.
9448 * autom4te Invocation:: A @acronym{GNU} M4 wrapper
9449 * Customizing autom4te:: Customizing the Autoconf package
9452 @node autom4te Invocation
9453 @subsection Invoking @command{autom4te}
9455 The command line arguments are modeled after M4's:
9458 autom4te @var{options} @var{files}
9463 where the @var{files} are directly passed to @command{m4}. By default,
9464 @acronym{GNU} M4 is found during configuration, but the environment
9466 @env{M4} can be set to tell @command{autom4te} where to look. In addition
9467 to the regular expansion, it handles the replacement of the quadrigraphs
9468 (@pxref{Quadrigraphs}), and of @samp{__oline__}, the current line in the
9469 output. It supports an extended syntax for the @var{files}:
9472 @item @var{file}.m4f
9473 This file is an M4 frozen file. Note that @emph{all the previous files
9474 are ignored}. See the option @option{--melt} for the rationale.
9477 If found in the library path, the @var{file} is included for expansion,
9478 otherwise it is ignored instead of triggering a failure.
9483 Of course, it supports the Autoconf common subset of options:
9488 Print a summary of the command line options and exit.
9492 Print the version number of Autoconf and exit.
9496 Report processing steps.
9500 Don't remove the temporary files and be even more verbose.
9502 @item --include=@var{dir}
9504 Also look for input files in @var{dir}. Multiple invocations
9507 @item --output=@var{file}
9508 @itemx -o @var{file}
9509 Save output (script or trace) to @var{file}. The file @option{-} stands
9510 for the standard output.
9515 As an extension of @command{m4}, it includes the following options:
9518 @item --warnings=@var{category}
9519 @itemx -W @var{category}
9521 @c FIXME: Point to the M4sugar macros, not Autoconf's.
9522 Report the warnings related to @var{category} (which can actually be a
9523 comma separated list). @xref{Reporting Messages}, macro
9524 @code{AC_DIAGNOSE}, for a comprehensive list of categories. Special
9529 report all the warnings
9535 treats warnings as errors
9537 @item no-@var{category}
9538 disable warnings falling into @var{category}
9541 Warnings about @samp{syntax} are enabled by default, and the environment
9542 variable @env{WARNINGS}, a comma separated list of categories, is
9543 honored. @samp{autom4te -W @var{category}} actually
9544 behaves as if you had run:
9547 autom4te --warnings=syntax,$WARNINGS,@var{category}
9551 For example, if you want to disable defaults and @env{WARNINGS}
9552 of @command{autom4te}, but enable the warnings about obsolete
9553 constructs, you would use @option{-W none,obsolete}.
9556 @cindex Macro invocation stack
9557 @command{autom4te} displays a back trace for errors, but not for
9558 warnings; if you want them, just pass @option{-W error}.
9562 Do not use frozen files. Any argument @code{@var{file}.m4f} is
9563 replaced by @code{@var{file}.m4}. This helps tracing the macros which
9564 are executed only when the files are frozen, typically
9565 @code{m4_define}. For instance, running:
9568 autom4te --melt 1.m4 2.m4f 3.m4 4.m4f input.m4
9572 is roughly equivalent to running:
9575 m4 1.m4 2.m4 3.m4 4.m4 input.m4
9582 autom4te 1.m4 2.m4f 3.m4 4.m4f input.m4
9589 m4 --reload-state=4.m4f input.m4
9594 Produce a frozen state file. @command{autom4te} freezing is stricter
9595 than M4's: it must produce no warnings, and no output other than empty
9596 lines (a line with white space is @emph{not} empty) and comments
9597 (starting with @samp{#}). Unlike @command{m4}'s similarly-named option,
9598 this option takes no argument:
9601 autom4te 1.m4 2.m4 3.m4 --freeze --output=3.m4f
9608 m4 1.m4 2.m4 3.m4 --freeze-state=3.m4f
9611 @item --mode=@var{octal-mode}
9612 @itemx -m @var{octal-mode}
9613 Set the mode of the non-traces output to @var{octal-mode}; by default
9619 @cindex @file{autom4te.cache}
9620 As another additional feature over @command{m4}, @command{autom4te}
9621 caches its results. @acronym{GNU} M4 is able to produce a regular
9622 output and traces at the same time. Traces are heavily used in the
9623 @acronym{GNU} Build System: @command{autoheader} uses them to build
9624 @file{config.h.in}, @command{autoreconf} to determine what
9625 @acronym{GNU} Build System components are used, @command{automake} to
9626 ``parse'' @file{configure.ac} etc. To avoid recomputation,
9627 traces are cached while performing regular expansion,
9628 and conversely. This cache is (actually, the caches are) stored in
9629 the directory @file{autom4te.cache}. @emph{It can safely be removed}
9630 at any moment (especially if for some reason @command{autom4te}
9631 considers it is trashed).
9634 @item --cache=@var{directory}
9635 @itemx -C @var{directory}
9636 Specify the name of the directory where the result should be cached.
9637 Passing an empty value disables caching. Be sure to pass a relative
9638 file name, as for the time being, global caches are not supported.
9641 Don't cache the results.
9645 If a cache is used, consider it obsolete (but update it anyway).
9650 Because traces are so important to the @acronym{GNU} Build System,
9651 @command{autom4te} provides high level tracing features as compared to
9652 M4, and helps exploiting the cache:
9655 @item --trace=@var{macro}[:@var{format}]
9656 @itemx -t @var{macro}[:@var{format}]
9657 Trace the invocations of @var{macro} according to the @var{format}.
9658 Multiple @option{--trace} arguments can be used to list several macros.
9659 Multiple @option{--trace} arguments for a single macro are not
9660 cumulative; instead, you should just make @var{format} as long as
9663 The @var{format} is a regular string, with newlines if desired, and
9664 several special escape codes. It defaults to @samp{$f:$l:$n:$%}. It can
9665 use the following special escapes:
9669 The character @samp{$}.
9672 The file name from which @var{macro} is called.
9675 The line number from which @var{macro} is called.
9678 The depth of the @var{macro} call. This is an M4 technical detail that
9679 you probably don't want to know about.
9682 The name of the @var{macro}.
9685 The @var{num}th argument of the call to @var{macro}.
9689 @itemx $@{@var{separator}@}@@
9690 All the arguments passed to @var{macro}, separated by the character
9691 @var{sep} or the string @var{separator} (@samp{,} by default). Each
9692 argument is quoted, i.e., enclosed in a pair of square brackets.
9696 @itemx $@{@var{separator}@}*
9697 As above, but the arguments are not quoted.
9701 @itemx $@{@var{separator}@}%
9702 As above, but the arguments are not quoted, all new line characters in
9703 the arguments are smashed, and the default separator is @samp{:}.
9705 The escape @samp{$%} produces single-line trace outputs (unless you put
9706 newlines in the @samp{separator}), while @samp{$@@} and @samp{$*} do
9710 @xref{autoconf Invocation}, for examples of trace uses.
9712 @item --preselect=@var{macro}
9713 @itemx -p @var{macro}
9714 Cache the traces of @var{macro}, but do not enable traces. This is
9715 especially important to save CPU cycles in the future. For instance,
9716 when invoked, @command{autoconf} preselects all the macros that
9717 @command{autoheader}, @command{automake}, @command{autoreconf}, etc.,
9718 trace, so that running @command{m4} is not needed to trace them: the
9719 cache suffices. This results in a huge speed-up.
9724 @cindex Autom4te Library
9725 Finally, @command{autom4te} introduces the concept of @dfn{Autom4te
9726 libraries}. They consists in a powerful yet extremely simple feature:
9727 sets of combined command line arguments:
9730 @item --language=@var{language}
9731 @itemx -l @var{language}
9732 Use the @var{language} Autom4te library. Current languages include:
9736 create M4sugar output.
9739 create M4sh executable shell scripts.
9742 create Autotest executable test suites.
9744 @item Autoconf-without-aclocal-m4
9745 create Autoconf executable configure scripts without
9746 reading @file{aclocal.m4}.
9749 create Autoconf executable configure scripts. This language inherits
9750 all the characteristics of @code{Autoconf-without-aclocal-m4} and
9751 additionally reads @file{aclocal.m4}.
9754 @item --prepend-include=@var{dir}
9756 Prepend directory @var{dir} to the search path. This is used to include
9757 the language-specific files before any third-party macros.
9761 @cindex @file{autom4te.cfg}
9762 As an example, if Autoconf is installed in its default location,
9763 @file{/usr/local}, the command @samp{autom4te -l m4sugar foo.m4} is
9764 strictly equivalent to the command:
9767 autom4te --prepend-include /usr/local/share/autoconf \
9768 m4sugar/m4sugar.m4f --warnings syntax foo.m4
9772 Recursive expansion applies here: the command @samp{autom4te -l m4sh foo.m4}
9773 is the same as @samp{autom4te --language M4sugar m4sugar/m4sh.m4f
9777 autom4te --prepend-include /usr/local/share/autoconf \
9778 m4sugar/m4sugar.m4f m4sugar/m4sh.m4f --mode 777 foo.m4
9782 The definition of the languages is stored in @file{autom4te.cfg}.
9784 @node Customizing autom4te
9785 @subsection Customizing @command{autom4te}
9787 One can customize @command{autom4te} via @file{~/.autom4te.cfg} (i.e.,
9788 as found in the user home directory), and @file{./.autom4te.cfg} (i.e.,
9789 as found in the directory from which @command{autom4te} is run). The
9790 order is first reading @file{autom4te.cfg}, then @file{~/.autom4te.cfg},
9791 then @file{./.autom4te.cfg}, and finally the command line arguments.
9793 In these text files, comments are introduced with @code{#}, and empty
9794 lines are ignored. Customization is performed on a per-language basis,
9795 wrapped in between a @samp{begin-language: "@var{language}"},
9796 @samp{end-language: "@var{language}"} pair.
9798 Customizing a language stands for appending options (@pxref{autom4te
9799 Invocation}) to the current definition of the language. Options, and
9800 more generally arguments, are introduced by @samp{args:
9801 @var{arguments}}. You may use the traditional shell syntax to quote the
9804 As an example, to disable Autoconf caches (@file{autom4te.cache})
9805 globally, include the following lines in @file{~/.autom4te.cfg}:
9808 ## ------------------ ##
9809 ## User Preferences. ##
9810 ## ------------------ ##
9812 begin-language: "Autoconf-without-aclocal-m4"
9814 end-language: "Autoconf-without-aclocal-m4"
9818 @node Programming in M4sugar
9819 @section Programming in M4sugar
9822 M4 by itself provides only a small, but sufficient, set of all-purpose
9823 macros. M4sugar introduces additional generic macros. Its name was
9824 coined by Lars J. Aas: ``Readability And Greater Understanding Stands 4
9828 * Redefined M4 Macros:: M4 builtins changed in M4sugar
9829 * Looping constructs:: Iteration in M4
9830 * Evaluation Macros:: More quotation and evaluation control
9831 * Text processing Macros:: String manipulation in M4
9832 * Forbidden Patterns:: Catching unexpanded macros
9835 @node Redefined M4 Macros
9836 @subsection Redefined M4 Macros
9858 With a few exceptions, all the M4 native macros are moved in the
9859 @samp{m4_} pseudo-namespace, e.g., M4sugar renames @code{define} as
9860 @code{m4_define} etc.
9862 Some M4 macros are redefined, and are slightly incompatible with their
9867 This macro kept its original name: no @code{m4_dnl} is defined.
9870 @defmac m4_defn (@var{macro})
9872 Unlike the M4 builtin, this macro fails if @var{macro} is not
9873 defined. See @code{m4_undefine}.
9876 @defmac m4_exit (@var{exit-status})
9878 This macro corresponds to @code{m4exit}.
9881 @defmac m4_if (@var{comment})
9882 @defmacx m4_if (@var{string-1}, @var{string-2}, @var{equal}, @ovar{not-equal})
9883 @defmacx m4_if (@var{string-1}, @var{string-2}, @var{equal}, @dots{})
9885 This macro corresponds to @code{ifelse}.
9888 @defmac m4_include (@var{file})
9889 @defmacx m4_sinclude (@var{file})
9892 Like the M4 builtins, but warn against multiple inclusions of @var{file}.
9895 @defmac m4_bpatsubst (@var{string}, @var{regexp}, @ovar{replacement})
9897 This macro corresponds to @code{patsubst}. The name @code{m4_patsubst}
9898 is kept for future versions of M4sh, on top of @acronym{GNU} M4 which will
9899 provide extended regular expression syntax via @code{epatsubst}.
9902 @defmac m4_popdef (@var{macro})
9904 Unlike the M4 builtin, this macro fails if @var{macro} is not
9905 defined. See @code{m4_undefine}.
9908 @defmac m4_bregexp (@var{string}, @var{regexp}, @ovar{replacement})
9910 This macro corresponds to @code{regexp}. The name @code{m4_regexp}
9911 is kept for future versions of M4sh, on top of @acronym{GNU} M4 which will
9912 provide extended regular expression syntax via @code{eregexp}.
9915 @defmac m4_wrap (@var{text})
9917 This macro corresponds to @code{m4wrap}.
9919 Posix requires arguments of multiple @code{m4wrap} calls to be
9920 reprocessed at @acronym{EOF} in the same order as the original calls.
9921 @acronym{GNU} M4 versions through 1.4.x, however, reprocess them in
9922 reverse order. Your code should not depend on the order.
9924 Also, Posix requires @code{m4wrap} to ignore its second and succeeding
9925 arguments, but @acronym{GNU} M4 versions through 1.4.x concatenate the
9926 arguments with intervening spaces. Your code should not pass more than
9929 You are encouraged to end @var{text} with @samp{[]}, to avoid unexpected
9930 token pasting between consecutive invocations of @code{m4_wrap}, as in:
9933 m4_define([foo], [bar])
9934 m4_define([foofoo], [OUCH])
9941 @defmac m4_undefine (@var{macro})
9943 Unlike the M4 builtin, this macro fails if @var{macro} is not
9947 m4_ifdef([@var{macro}], [m4_undefine([@var{macro}])])
9951 to recover the behavior of the builtin.
9954 @defmac m4_maketemp (@var{template})
9955 @defmacx m4_mkstemp (@var{template})
9958 Posix requires @code{maketemp} to replace the trailing @samp{X}
9959 characters in @var{template} with the process id, without regards to the
9960 existence of a file by that name, but this a security hole. When this
9961 was pointed out to the Posix folks, they agreed to invent a new macro
9962 @code{mkstemp} that always creates a uniquely named file, but not all
9963 versions of @acronym{GNU} M4 support the new macro. In M4sugar,
9964 @code{m4_maketemp} and @code{m4_mkstemp} are synonyms for each other,
9965 and both have the secure semantics regardless of which macro the
9966 underlying M4 provides.
9970 @node Looping constructs
9971 @subsection Looping constructs
9973 The following macros implement loops in M4.
9975 @defmac m4_for (@var{var}, @var{first}, @var{last}, @ovar{step}, @var{expression})
9977 Loop over the numeric values between @var{first} and @var{last}
9978 including bounds by increments of @var{step}. For each iteration,
9979 expand @var{expression} with the numeric value assigned to @var{var}.
9980 If @var{step} is omitted, it defaults to @samp{1} or @samp{-1} depending
9981 on the order of the limits. If given, @var{step} has to match this
9985 @defmac m4_foreach (@var{var}, @var{list}, @var{expression})
9987 Loop over the comma-separated M4 list @var{list}, assigning each value
9988 to @var{var}, and expand @var{expression}. The following example
9992 m4_foreach([myvar], [[foo], [bar, baz]],
9999 @defmac m4_foreach_w (@var{var}, @var{list}, @var{expression})
10000 @msindex{foreach_w}
10001 Loop over the white-space-separated list @var{list}, assigning each value
10002 to @var{var}, and expand @var{expression}.
10004 The deprecated macro @code{AC_FOREACH} is an alias of
10005 @code{m4_foreach_w}.
10010 @node Evaluation Macros
10011 @subsection Evaluation Macros
10013 The following macros give some control over the order of the evaluation
10014 by adding or removing levels of quotes. They are meant for hard-core M4
10017 @defmac m4_dquote (@var{arg1}, @dots{})
10019 Return the arguments as a quoted list of quoted arguments.
10022 @defmac m4_quote (@var{arg1}, @dots{})
10024 Return the arguments as a single entity, i.e., wrap them into a pair of
10028 The following example aims at emphasizing the difference between (i), not
10029 using these macros, (ii), using @code{m4_quote}, and (iii), using
10033 $ @kbd{cat example.m4}
10034 # Overquote, so that quotes are visible.
10035 m4_define([show], [$[]1 = [$1], $[]@@ = [$@@]])
10036 m4_define([mkargs], [1, 2, 3])
10037 m4_define([arg1], [[$1]])
10040 show(m4_quote(a, b))
10041 show(m4_dquote(a, b))
10044 arg1(m4_defn([mkargs]))
10045 arg1(m4_quote(mkargs))
10046 arg1(m4_dquote(mkargs))
10047 $ @kbd{autom4te -l m4sugar example.m4}
10048 $1 = a, $@@ = [a],[b]
10049 $1 = a,b, $@@ = [a,b]
10050 $1 = [a],[b], $@@ = [[a],[b]]
10060 @node Text processing Macros
10061 @subsection Text processing Macros
10063 The following macros may be used to manipulate strings in M4.
10064 They are not intended for casual use.
10066 @defmac m4_re_escape (@var{string})
10067 @msindex{re_escape}
10068 Backslash-escape all characters in @var{string} that are active in
10072 @defmac m4_tolower (@var{string})
10073 @defmacx m4_toupper (@var{string})
10076 Return @var{string} with letters converted to upper or lower case,
10080 @defmac m4_split (@var{string}, @ovar{regexp})
10082 Split @var{string} into an M4 list of elements quoted by @samp{[} and
10083 @samp{]}, while keeping white space at the beginning and at the end.
10084 If @var{regexp} is given, use it instead of @samp{[\t ]+} for splitting.
10085 If @var{string} is empty, the result is an empty list.
10088 @defmac m4_normalize (@var{string})
10089 @msindex{normalize}
10090 Remove leading and trailing spaces and tabs, sequences of
10091 backslash-then-newline, and replace multiple spaces and tabs with a
10095 @defmac m4_append (@var{macro-name}, @var{string}, @ovar{separator})
10096 @defmacx m4_append_uniq (@var{macro-name}, @var{string}, @ovar{separator})
10098 @msindex{append_uniq}
10099 Redefine @var{macro-name} to its former contents with @var{separator}
10100 and @var{string} added at the end. If @var{macro-name} was undefined
10101 before (but not if it was defined but empty), then no @var{separator} is
10102 added. @code{m4_append} can be used to grow strings, and
10103 @code{m4_append_uniq} to grow strings without duplicating substrings.
10108 @node Forbidden Patterns
10109 @subsection Forbidden Patterns
10110 @cindex Forbidden patterns
10111 @cindex Patterns, forbidden
10113 M4sugar provides a means to define suspicious patterns, patterns
10114 describing tokens which should not be found in the output. For
10115 instance, if an Autoconf @file{configure} script includes tokens such as
10116 @samp{AC_DEFINE}, or @samp{dnl}, then most probably something went
10117 wrong (typically a macro was not evaluated because of overquotation).
10119 M4sugar forbids all the tokens matching @samp{^m4_} and @samp{^dnl$}.
10121 @defmac m4_pattern_forbid (@var{pattern})
10122 @msindex{pattern_forbid}
10123 Declare that no token matching @var{pattern} must be found in the output.
10124 Comments are not checked; this can be a problem if, for instance, you
10125 have some macro left unexpanded after an @samp{#include}. No consensus
10126 is currently found in the Autoconf community, as some people consider it
10127 should be valid to name macros in comments (which doesn't make sense to
10128 the author of this documentation, as @samp{#}-comments should document
10129 the output, not the input, documented by @samp{dnl} comments).
10132 Of course, you might encounter exceptions to these generic rules, for
10133 instance you might have to refer to @samp{$m4_flags}.
10135 @defmac m4_pattern_allow (@var{pattern})
10136 @msindex{pattern_allow}
10137 Any token matching @var{pattern} is allowed, including if it matches an
10138 @code{m4_pattern_forbid} pattern.
10141 @node Programming in M4sh
10142 @section Programming in M4sh
10144 @c FIXME: Eventually will become a chapter, as it is not related to
10145 @c programming in M4 per se.
10147 M4sh, pronounced ``mash'', is aiming at producing portable Bourne shell
10148 scripts. This name was coined by Lars J. Aas, who notes that,
10149 according to the Webster's Revised Unabridged Dictionary (1913):
10152 Mash \Mash\, n. [Akin to G. meisch, maisch, meische, maische, mash,
10153 wash, and prob.@: to AS. miscian to mix. See ``Mix''.]
10157 A mass of mixed ingredients reduced to a soft pulpy state by beating or
10161 A mixture of meal or bran and water fed to animals.
10164 A mess; trouble. [Obs.] --Beau.@: & Fl.
10169 For the time being, it is not mature enough to be widely used.
10171 M4sh provides portable alternatives for some common shell constructs
10172 that unfortunately are not portable in practice.
10174 @c Deprecated, to be replaced by a better API
10176 @defmac AS_BASENAME (@var{file-name})
10178 Output the non-directory portion of @var{file-name}. For example,
10179 if @code{$file} is @samp{/one/two/three}, the command
10180 @code{base=`AS_BASENAME(["$file"])`} sets @code{base} to @samp{three}.
10184 @defmac AS_BOURNE_COMPATIBLE
10185 @asindex{BOURNE_COMPATIBLE}
10186 Set up the shell to be more compatible with the Bourne shell as
10187 standardized by Posix, if possible. This may involve setting
10188 environment variables, or setting options, or similar
10189 implementation-specific actions.
10192 @defmac AS_CASE (@var{word}, @ovar{pattern1}, @ovar{if-matched1}, @dots{}, @ovar{default})
10194 Expand into a shell @samp{case} statement, where @var{word} is matched
10195 against one or more patterns. @var{if-matched} is run if the
10196 corresponding pattern matched @var{word}, else @var{default} is run.
10199 @defmac AS_DIRNAME (@var{file-name})
10201 Output the directory portion of @var{file-name}. For example,
10202 if @code{$file} is @samp{/one/two/three}, the command
10203 @code{dir=`AS_DIRNAME(["$file"])`} sets @code{dir} to @samp{/one/two}.
10206 @defmac AS_IF (@var{test1}, @ovar{run-if-true1}, @dots{}, @ovar{run-if-false})
10208 Run shell code @var{test1}. If @var{test1} exits with a zero status then
10209 run shell code @var{run-if-true1}, else examine further tests. If no test
10210 exits with a zero status, run shell code @var{run-if-false}, with
10211 simplifications if either @var{run-if-true1} or @var{run-if-false1}
10212 is empty. For example,
10215 AS_IF([test "$foo" = yes], [HANDLE_FOO([yes])],
10216 [test "$foo" != no], [HANDLE_FOO([maybe])],
10217 [echo foo not specified])
10221 ensures any required macros of @code{HANDLE_FOO}
10222 are expanded before the first test.
10225 @defmac AS_MKDIR_P (@var{file-name})
10227 Make the directory @var{file-name}, including intervening directories
10228 as necessary. This is equivalent to @samp{mkdir -p @var{file-name}},
10229 except that it is portable to older versions of @command{mkdir} that
10230 lack support for the @option{-p} option. Also, @code{AS_MKDIR_P}
10231 succeeds if @var{file-name} is a symbolic link to an existing directory,
10232 even though Posix is unclear whether @samp{mkdir -p} should
10233 succeed in that case. If creation of @var{file-name} fails, exit the
10236 Also see the @code{AC_PROG_MKDIR_P} macro (@pxref{Particular Programs}).
10239 @defmac AS_SHELL_SANITIZE
10240 @asindex{SHELL_SANITIZE}
10241 Initialize the shell suitably for @code{configure} scripts. This has
10242 the effect of @code{AS_BOURNE_COMPATIBLE}, and sets some other
10243 environment variables for predictable results from configuration tests.
10244 For example, it sets @env{LC_ALL} to change to the default C locale.
10245 @xref{Special Shell Variables}.
10248 @defmac AS_TR_CPP (@var{expression})
10250 Transform @var{expression} into a valid right-hand side for a C @code{#define}.
10254 # This outputs "#define HAVE_CHAR_P 1".
10256 echo "#define AS_TR_CPP([HAVE_$type]) 1"
10260 @defmac AS_TR_SH (@var{expression})
10262 Transform @var{expression} into a valid shell variable name. For example:
10265 # This outputs "Have it!".
10266 header="sys/some file.h"
10267 AS_TR_SH([HAVE_$header])=yes
10268 if test "$HAVE_sys_some_file_h" = yes; then echo "Have it!"; fi
10272 @defmac AS_SET_CATFILE (@var{var}, @var{dir}, @var{file})
10273 @asindex{SET_CATFILE}
10274 Set the shell variable @var{var} to @var{dir}/@var{file}, but
10275 optimizing the common cases (@var{dir} or @var{file} is @samp{.},
10276 @var{file} is absolute, etc.).
10280 @node File Descriptor Macros
10281 @section File Descriptor Macros
10283 @cindex standard input
10284 @cindex file descriptors
10285 @cindex descriptors
10286 @cindex low-level output
10287 @cindex output, low-level
10289 The following macros define file descriptors used to output messages
10290 (or input values) from @file{configure} scripts.
10294 echo "$wombats found" >&AS_MESSAGE_LOG_FD
10295 echo 'Enter desired kangaroo count:' >&AS_MESSAGE_FD
10296 read kangaroos <&AS_ORIGINAL_STDIN_FD`
10300 However doing so is seldom needed, because Autoconf provides higher
10301 level macros as described below.
10303 @defmac AS_MESSAGE_FD
10304 @asindex{MESSAGE_FD}
10305 The file descriptor for @samp{checking for...} messages and results.
10306 Normally this directs messages to the standard output, however when
10307 @command{configure} is run with the @option{-q} option, messages sent to
10308 @code{AS_MESSAGE_FD} are discarded.
10310 If you want to display some messages, consider using one of the printing
10311 macros (@pxref{Printing Messages}) instead. Copies of messages output
10312 via these macros are also recorded in @file{config.log}.
10315 @defmac AS_MESSAGE_LOG_FD
10316 @asindex{MESSAGE_LOG_FD}
10318 The file descriptor for messages logged to @file{config.log}. Macros
10319 that run tools, like @code{AC_COMPILE_IFELSE} (@pxref{Running the
10320 Compiler}), redirect all output to this descriptor. You may want to do
10321 so if you develop such a low-level macro.
10324 @defmac AS_ORIGINAL_STDIN_FD
10325 @asindex{ORIGINAL_STDIN_FD}
10326 The file descriptor for the original standard input.
10328 When @command{configure} runs, it may accidentally execute an
10329 interactive command that has the same name as the non-interactive meant
10330 to be used or checked. If the standard input was the terminal, such
10331 interactive programs would cause @command{configure} to stop, pending
10332 some user input. Therefore @command{configure} redirects its standard
10333 input from @file{/dev/null} during its initialization. This is not
10334 normally a problem, since @command{configure} normally does not need
10337 In the extreme case where your @file{configure} script really needs to
10338 obtain some values from the original standard input, you can read them
10339 explicitly from @code{AS_ORIGINAL_STDIN_FD}.
10343 @c =================================================== Writing Autoconf Macros.
10345 @node Writing Autoconf Macros
10346 @chapter Writing Autoconf Macros
10348 When you write a feature test that could be applicable to more than one
10349 software package, the best thing to do is encapsulate it in a new macro.
10350 Here are some instructions and guidelines for writing Autoconf macros.
10353 * Macro Definitions:: Basic format of an Autoconf macro
10354 * Macro Names:: What to call your new macros
10355 * Reporting Messages:: Notifying @command{autoconf} users
10356 * Dependencies Between Macros:: What to do when macros depend on other macros
10357 * Obsoleting Macros:: Warning about old ways of doing things
10358 * Coding Style:: Writing Autoconf macros @`a la Autoconf
10361 @node Macro Definitions
10362 @section Macro Definitions
10365 Autoconf macros are defined using the @code{AC_DEFUN} macro, which is
10366 similar to the M4 builtin @code{m4_define} macro. In addition to
10367 defining a macro, @code{AC_DEFUN} adds to it some code that is used to
10368 constrain the order in which macros are called (@pxref{Prerequisite
10371 An Autoconf macro definition looks like this:
10374 AC_DEFUN(@var{macro-name}, @var{macro-body})
10377 You can refer to any arguments passed to the macro as @samp{$1},
10378 @samp{$2}, etc. @xref{Definitions, , How to define new macros, m4.info,
10379 @acronym{GNU} M4}, for more complete information on writing M4 macros.
10381 Be sure to properly quote both the @var{macro-body} @emph{and} the
10382 @var{macro-name} to avoid any problems if the macro happens to have
10383 been previously defined.
10385 Each macro should have a header comment that gives its prototype, and a
10386 brief description. When arguments have default values, display them in
10387 the prototype. For example:
10390 # AC_MSG_ERROR(ERROR, [EXIT-STATUS = 1])
10391 # --------------------------------------
10392 m4_define([AC_MSG_ERROR],
10393 [@{ AS_MESSAGE([error: $1], [2])
10394 exit m4_default([$2], [1]); @}])
10397 Comments about the macro should be left in the header comment. Most
10398 other comments make their way into @file{configure}, so just keep
10399 using @samp{#} to introduce comments.
10402 If you have some special comments about pure M4 code, comments
10403 that make no sense in @file{configure} and in the header comment, then
10404 use the builtin @code{dnl}: it causes M4 to discard the text
10405 through the next newline.
10407 Keep in mind that @code{dnl} is rarely needed to introduce comments;
10408 @code{dnl} is more useful to get rid of the newlines following macros
10409 that produce no output, such as @code{AC_REQUIRE}.
10413 @section Macro Names
10415 All of the Autoconf macros have all-uppercase names starting with
10416 @samp{AC_} to prevent them from accidentally conflicting with other
10417 text. All shell variables that they use for internal purposes have
10418 mostly-lowercase names starting with @samp{ac_}. To ensure that your
10419 macros don't conflict with present or future Autoconf macros, you should
10420 prefix your own macro names and any shell variables they use with some
10421 other sequence. Possibilities include your initials, or an abbreviation
10422 for the name of your organization or software package.
10424 Most of the Autoconf macros' names follow a structured naming convention
10425 that indicates the kind of feature check by the name. The macro names
10426 consist of several words, separated by underscores, going from most
10427 general to most specific. The names of their cache variables use the
10428 same convention (@pxref{Cache Variable Names}, for more information on
10431 The first word of the name after @samp{AC_} usually tells the category
10432 of the feature being tested. Here are the categories used in Autoconf for
10433 specific test macros, the kind of macro that you are more likely to
10434 write. They are also used for cache variables, in all-lowercase. Use
10435 them where applicable; where they're not, invent your own categories.
10439 C language builtin features.
10441 Declarations of C variables in header files.
10443 Functions in libraries.
10445 Posix group owners of files.
10451 Absolute names of files, including programs.
10453 The base names of programs.
10455 Members of aggregates.
10457 Operating system features.
10459 C builtin or declared types.
10461 C variables in libraries.
10464 After the category comes the name of the particular feature being
10465 tested. Any further words in the macro name indicate particular aspects
10466 of the feature. For example, @code{AC_PROG_CC_STDC} checks whether the
10467 C compiler supports @acronym{ISO} Standard C.
10469 An internal macro should have a name that starts with an underscore;
10470 Autoconf internals should therefore start with @samp{_AC_}.
10471 Additionally, a macro that is an internal subroutine of another macro
10472 should have a name that starts with an underscore and the name of that
10473 other macro, followed by one or more words saying what the internal
10474 macro does. For example, @code{AC_PATH_X} has internal macros
10475 @code{_AC_PATH_X_XMKMF} and @code{_AC_PATH_X_DIRECT}.
10477 @node Reporting Messages
10478 @section Reporting Messages
10479 @cindex Messages, from @command{autoconf}
10481 When macros statically diagnose abnormal situations, benign or fatal,
10482 they should report them using these macros. For dynamic issues, i.e.,
10483 when @command{configure} is run, see @ref{Printing Messages}.
10485 @defmac AC_DIAGNOSE (@var{category}, @var{message})
10487 Report @var{message} as a warning (or as an error if requested by the
10488 user) if warnings of the @var{category} are turned on. You are
10489 encouraged to use standard categories, which currently include:
10493 messages that don't fall into one of the following categories. Use of an
10494 empty @var{category} is equivalent.
10497 related to cross compilation issues.
10500 use of an obsolete construct.
10503 dubious syntactic constructs, incorrectly ordered macro calls.
10507 @defmac AC_WARNING (@var{message})
10509 Equivalent to @samp{AC_DIAGNOSE([syntax], @var{message})}, but you are
10510 strongly encouraged to use a finer grained category.
10513 @defmac AC_FATAL (@var{message})
10515 Report a severe error @var{message}, and have @command{autoconf} die.
10518 When the user runs @samp{autoconf -W error}, warnings from
10519 @code{AC_DIAGNOSE} and @code{AC_WARNING} are reported as error, see
10520 @ref{autoconf Invocation}.
10522 @node Dependencies Between Macros
10523 @section Dependencies Between Macros
10524 @cindex Dependencies between macros
10526 Some Autoconf macros depend on other macros having been called first in
10527 order to work correctly. Autoconf provides a way to ensure that certain
10528 macros are called if needed and a way to warn the user if macros are
10529 called in an order that might cause incorrect operation.
10532 * Prerequisite Macros:: Ensuring required information
10533 * Suggested Ordering:: Warning about possible ordering problems
10534 * One-Shot Macros:: Ensuring a macro is called only once
10537 @node Prerequisite Macros
10538 @subsection Prerequisite Macros
10539 @cindex Prerequisite macros
10540 @cindex Macros, prerequisites
10542 A macro that you write might need to use values that have previously
10543 been computed by other macros. For example, @code{AC_DECL_YYTEXT}
10544 examines the output of @code{flex} or @code{lex}, so it depends on
10545 @code{AC_PROG_LEX} having been called first to set the shell variable
10548 Rather than forcing the user of the macros to keep track of the
10549 dependencies between them, you can use the @code{AC_REQUIRE} macro to do
10550 it automatically. @code{AC_REQUIRE} can ensure that a macro is only
10551 called if it is needed, and only called once.
10553 @defmac AC_REQUIRE (@var{macro-name})
10555 If the M4 macro @var{macro-name} has not already been called, call it
10556 (without any arguments). Make sure to quote @var{macro-name} with
10557 square brackets. @var{macro-name} must have been defined using
10558 @code{AC_DEFUN} or else contain a call to @code{AC_PROVIDE} to indicate
10559 that it has been called.
10561 @code{AC_REQUIRE} must be used inside a macro defined by @code{AC_DEFUN}; it
10562 must not be called from the top level.
10565 @code{AC_REQUIRE} is often misunderstood. It really implements
10566 dependencies between macros in the sense that if one macro depends upon
10567 another, the latter is expanded @emph{before} the body of the
10568 former. To be more precise, the required macro is expanded before
10569 the outermost defined macro in the current expansion stack.
10570 In particular, @samp{AC_REQUIRE([FOO])} is not replaced with the body of
10571 @code{FOO}. For instance, this definition of macros:
10575 AC_DEFUN([TRAVOLTA],
10576 [test "$body_temperature_in_celsius" -gt "38" &&
10577 dance_floor=occupied])
10578 AC_DEFUN([NEWTON_JOHN],
10579 [test "$hair_style" = "curly" &&
10580 dance_floor=occupied])
10584 AC_DEFUN([RESERVE_DANCE_FLOOR],
10585 [if date | grep '^Sat.*pm' >/dev/null 2>&1; then
10586 AC_REQUIRE([TRAVOLTA])
10587 AC_REQUIRE([NEWTON_JOHN])
10593 with this @file{configure.ac}
10596 AC_INIT([Dance Manager], [1.0], [bug-dance@@example.org])
10597 RESERVE_DANCE_FLOOR
10598 if test "$dance_floor" = occupied; then
10599 AC_MSG_ERROR([cannot pick up here, let's move])
10604 does not leave you with a better chance to meet a kindred soul at
10605 other times than Saturday night since it expands into:
10609 test "$body_temperature_in_Celsius" -gt "38" &&
10610 dance_floor=occupied
10611 test "$hair_style" = "curly" &&
10612 dance_floor=occupied
10614 if date | grep '^Sat.*pm' >/dev/null 2>&1; then
10621 This behavior was chosen on purpose: (i) it prevents messages in
10622 required macros from interrupting the messages in the requiring macros;
10623 (ii) it avoids bad surprises when shell conditionals are used, as in:
10628 AC_REQUIRE([SOME_CHECK])
10635 The helper macros @code{AS_IF} and @code{AS_CASE} may be used to
10636 enforce expansion of required macros outside of shell conditional
10637 constructs. You are furthermore encouraged to put all @code{AC_REQUIRE} calls
10638 at the beginning of a macro. You can use @code{dnl} to avoid the empty
10641 @node Suggested Ordering
10642 @subsection Suggested Ordering
10643 @cindex Macros, ordering
10644 @cindex Ordering macros
10646 Some macros should be run before another macro if both are called, but
10647 neither @emph{requires} that the other be called. For example, a macro
10648 that changes the behavior of the C compiler should be called before any
10649 macros that run the C compiler. Many of these dependencies are noted in
10652 Autoconf provides the @code{AC_BEFORE} macro to warn users when macros
10653 with this kind of dependency appear out of order in a
10654 @file{configure.ac} file. The warning occurs when creating
10655 @command{configure} from @file{configure.ac}, not when running
10656 @command{configure}.
10658 For example, @code{AC_PROG_CPP} checks whether the C compiler
10659 can run the C preprocessor when given the @option{-E} option. It should
10660 therefore be called after any macros that change which C compiler is
10661 being used, such as @code{AC_PROG_CC}. So @code{AC_PROG_CC} contains:
10664 AC_BEFORE([$0], [AC_PROG_CPP])dnl
10668 This warns the user if a call to @code{AC_PROG_CPP} has already occurred
10669 when @code{AC_PROG_CC} is called.
10671 @defmac AC_BEFORE (@var{this-macro-name}, @var{called-macro-name})
10673 Make M4 print a warning message to the standard error output if
10674 @var{called-macro-name} has already been called. @var{this-macro-name}
10675 should be the name of the macro that is calling @code{AC_BEFORE}. The
10676 macro @var{called-macro-name} must have been defined using
10677 @code{AC_DEFUN} or else contain a call to @code{AC_PROVIDE} to indicate
10678 that it has been called.
10681 @node One-Shot Macros
10682 @subsection One-Shot Macros
10683 @cindex One-shot macros
10684 @cindex Macros, called once
10686 Some macros should be called only once, either because calling them
10687 multiple time is unsafe, or because it is bad style. For instance
10688 Autoconf ensures that @code{AC_CANONICAL_BUILD} and cousins
10689 (@pxref{Canonicalizing}) are evaluated only once, because it makes no
10690 sense to run these expensive checks more than once. Such one-shot
10691 macros can be defined using @code{AC_DEFUN_ONCE}.
10693 @defmac AC_DEFUN_ONCE (@var{macro-name}, @var{macro-body})
10694 @acindex{DEFUN_ONCE}
10696 Declare macro @var{macro-name} like @code{AC_DEFUN} would (@pxref{Macro
10697 Definitions}), and emit a warning any time the macro is called more than
10701 Obviously it is not sensible to evaluate a macro defined by
10702 @code{AC_DEFUN_ONCE} in a macro defined by @code{AC_DEFUN}.
10703 Most of the time you want to use @code{AC_REQUIRE} (@pxref{Prerequisite
10706 @node Obsoleting Macros
10707 @section Obsoleting Macros
10708 @cindex Obsoleting macros
10709 @cindex Macros, obsoleting
10711 Configuration and portability technology has evolved over the years.
10712 Often better ways of solving a particular problem are developed, or
10713 ad-hoc approaches are systematized. This process has occurred in many
10714 parts of Autoconf. One result is that some of the macros are now
10715 considered @dfn{obsolete}; they still work, but are no longer considered
10716 the best thing to do, hence they should be replaced with more modern
10717 macros. Ideally, @command{autoupdate} should replace the old macro calls
10718 with their modern implementation.
10720 Autoconf provides a simple means to obsolete a macro.
10722 @defmac AU_DEFUN (@var{old-macro}, @var{implementation}, @ovar{message})
10724 Define @var{old-macro} as @var{implementation}. The only difference
10725 with @code{AC_DEFUN} is that the user is warned that
10726 @var{old-macro} is now obsolete.
10728 If she then uses @command{autoupdate}, the call to @var{old-macro} is
10729 replaced by the modern @var{implementation}. @var{message} should
10730 include information on what to do after running @command{autoupdate};
10731 @command{autoupdate} prints it as a warning, and includes it
10732 in the updated @file{configure.ac} file.
10734 The details of this macro are hairy: if @command{autoconf} encounters an
10735 @code{AU_DEFUN}ed macro, all macros inside its second argument are expanded
10736 as usual. However, when @command{autoupdate} is run, only M4 and M4sugar
10737 macros are expanded here, while all other macros are disabled and
10738 appear literally in the updated @file{configure.ac}.
10741 @defmac AU_ALIAS (@var{old-name}, @var{new-name})
10743 Used if the @var{old-name} is to be replaced by a call to @var{new-macro}
10744 with the same parameters. This happens for example if the macro was renamed.
10748 @section Coding Style
10749 @cindex Coding style
10751 The Autoconf macros follow a strict coding style. You are encouraged to
10752 follow this style, especially if you intend to distribute your macro,
10753 either by contributing it to Autoconf itself, or via other means.
10755 The first requirement is to pay great attention to the quotation. For
10756 more details, see @ref{Autoconf Language}, and @ref{M4 Quotation}.
10758 Do not try to invent new interfaces. It is likely that there is a macro
10759 in Autoconf that resembles the macro you are defining: try to stick to
10760 this existing interface (order of arguments, default values, etc.). We
10761 @emph{are} conscious that some of these interfaces are not perfect;
10762 nevertheless, when harmless, homogeneity should be preferred over
10765 Be careful about clashes both between M4 symbols and between shell
10768 If you stick to the suggested M4 naming scheme (@pxref{Macro Names}),
10769 you are unlikely to generate conflicts. Nevertheless, when you need to
10770 set a special value, @emph{avoid using a regular macro name}; rather,
10771 use an ``impossible'' name. For instance, up to version 2.13, the macro
10772 @code{AC_SUBST} used to remember what @var{symbol} macros were already defined
10773 by setting @code{AC_SUBST_@var{symbol}}, which is a regular macro name.
10774 But since there is a macro named @code{AC_SUBST_FILE}, it was just
10775 impossible to @samp{AC_SUBST(FILE)}! In this case,
10776 @code{AC_SUBST(@var{symbol})} or @code{_AC_SUBST(@var{symbol})} should
10777 have been used (yes, with the parentheses).
10778 @c or better yet, high-level macros such as @code{m4_expand_once}
10780 No Autoconf macro should ever enter the user-variable name space; i.e.,
10781 except for the variables that are the actual result of running the
10782 macro, all shell variables should start with @code{ac_}. In
10783 addition, small macros or any macro that is likely to be embedded in
10784 other macros should be careful not to use obvious names.
10787 Do not use @code{dnl} to introduce comments: most of the comments you
10788 are likely to write are either header comments which are not output
10789 anyway, or comments that should make their way into @file{configure}.
10790 There are exceptional cases where you do want to comment special M4
10791 constructs, in which case @code{dnl} is right, but keep in mind that it
10794 M4 ignores the leading blanks and newlines before each argument.
10795 Use this feature to
10796 indent in such a way that arguments are (more or less) aligned with the
10797 opening parenthesis of the macro being called. For instance, instead of
10800 AC_CACHE_CHECK(for EMX OS/2 environment,
10802 [AC_COMPILE_IFELSE([AC_LANG_PROGRAM(, [return __EMX__;])],
10803 [ac_cv_emxos2=yes], [ac_cv_emxos2=no])])
10810 AC_CACHE_CHECK([for EMX OS/2 environment], [ac_cv_emxos2],
10811 [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [return __EMX__;])],
10812 [ac_cv_emxos2=yes],
10813 [ac_cv_emxos2=no])])
10820 AC_CACHE_CHECK([for EMX OS/2 environment],
10822 [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([],
10823 [return __EMX__;])],
10824 [ac_cv_emxos2=yes],
10825 [ac_cv_emxos2=no])])
10828 When using @code{AC_RUN_IFELSE} or any macro that cannot work when
10829 cross-compiling, provide a pessimistic value (typically @samp{no}).
10831 Feel free to use various tricks to prevent auxiliary tools, such as
10832 syntax-highlighting editors, from behaving improperly. For instance,
10836 m4_bpatsubst([$1], [$"])
10843 m4_bpatsubst([$1], [$""])
10847 so that Emacsen do not open an endless ``string'' at the first quote.
10848 For the same reasons, avoid:
10858 test $[@@%:@@] != 0
10862 Otherwise, the closing bracket would be hidden inside a @samp{#}-comment,
10863 breaking the bracket-matching highlighting from Emacsen. Note the
10864 preferred style to escape from M4: @samp{$[1]}, @samp{$[@@]}, etc. Do
10865 not escape when it is unnecessary. Common examples of useless quotation
10866 are @samp{[$]$1} (write @samp{$$1}), @samp{[$]var} (use @samp{$var}),
10867 etc. If you add portability issues to the picture, you'll prefer
10868 @samp{$@{1+"$[@@]"@}} to @samp{"[$]@@"}, and you'll prefer do something
10869 better than hacking Autoconf @code{:-)}.
10871 When using @command{sed}, don't use @option{-e} except for indenting
10872 purposes. With the @code{s} and @code{y} commands, the preferred
10873 separator is @samp{/} unless @samp{/} itself might appear in the pattern
10874 or replacement, in which case you should use @samp{|}, or optionally
10875 @samp{,} if you know the pattern and replacement cannot contain a file
10876 name. If none of these characters will do, choose a printable character
10877 that cannot appear in the pattern or replacement. Characters from the
10878 set @samp{"#$&'()*;<=>?`|~} are good choices if the pattern or
10879 replacement might contain a file name, since they have special meaning
10880 to the shell and are less likely to occur in file names.
10882 @xref{Macro Definitions}, for details on how to define a macro. If a
10883 macro doesn't use @code{AC_REQUIRE}, is expected to never be the object
10884 of an @code{AC_REQUIRE} directive, and macros required by other macros
10885 inside arguments do not need to be expanded before this macro, then
10886 use @code{m4_define}. In case of doubt, use @code{AC_DEFUN}.
10887 All the @code{AC_REQUIRE} statements should be at the beginning of the
10888 macro, and each statement should be followed by @code{dnl}.
10890 You should not rely on the number of arguments: instead of checking
10891 whether an argument is missing, test that it is not empty. It provides
10892 both a simpler and a more predictable interface to the user, and saves
10893 room for further arguments.
10895 Unless the macro is short, try to leave the closing @samp{])} at the
10896 beginning of a line, followed by a comment that repeats the name of the
10897 macro being defined. This introduces an additional newline in
10898 @command{configure}; normally, that is not a problem, but if you want to
10899 remove it you can use @samp{[]dnl} on the last line. You can similarly
10900 use @samp{[]dnl} after a macro call to remove its newline. @samp{[]dnl}
10901 is recommended instead of @samp{dnl} to ensure that M4 does not
10902 interpret the @samp{dnl} as being attached to the preceding text or
10903 macro output. For example, instead of:
10906 AC_DEFUN([AC_PATH_X],
10907 [AC_MSG_CHECKING([for X])
10909 @r{# @dots{}omitted@dots{}}
10910 AC_MSG_RESULT([libraries $x_libraries, headers $x_includes])
10918 AC_DEFUN([AC_PATH_X],
10919 [AC_REQUIRE_CPP()[]dnl
10920 AC_MSG_CHECKING([for X])
10921 @r{# @dots{}omitted@dots{}}
10922 AC_MSG_RESULT([libraries $x_libraries, headers $x_includes])
10927 If the macro is long, try to split it into logical chunks. Typically,
10928 macros that check for a bug in a function and prepare its
10929 @code{AC_LIBOBJ} replacement should have an auxiliary macro to perform
10930 this setup. Do not hesitate to introduce auxiliary macros to factor
10933 In order to highlight the recommended coding style, here is a macro
10934 written the old way:
10937 dnl Check for EMX on OS/2.
10939 AC_DEFUN(_AC_EMXOS2,
10940 [AC_CACHE_CHECK(for EMX OS/2 environment, ac_cv_emxos2,
10941 [AC_COMPILE_IFELSE([AC_LANG_PROGRAM(, return __EMX__;)],
10942 ac_cv_emxos2=yes, ac_cv_emxos2=no)])
10943 test "$ac_cv_emxos2" = yes && EMXOS2=yes])
10952 # Check for EMX on OS/2.
10953 m4_define([_AC_EMXOS2],
10954 [AC_CACHE_CHECK([for EMX OS/2 environment], [ac_cv_emxos2],
10955 [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [return __EMX__;])],
10956 [ac_cv_emxos2=yes],
10957 [ac_cv_emxos2=no])])
10958 test "$ac_cv_emxos2" = yes && EMXOS2=yes[]dnl
10965 @c ============================================= Portable Shell Programming
10967 @node Portable Shell
10968 @chapter Portable Shell Programming
10969 @cindex Portable shell programming
10971 When writing your own checks, there are some shell-script programming
10972 techniques you should avoid in order to make your code portable. The
10973 Bourne shell and upward-compatible shells like the Korn shell and Bash
10974 have evolved over the years, but to prevent trouble, do not take
10975 advantage of features that were added after Unix version 7, circa
10976 1977 (@pxref{Systemology}).
10978 You should not use shell functions, aliases, negated character
10979 classes, or other features that are not found in all Bourne-compatible
10980 shells; restrict yourself to the lowest common denominator. Even
10981 @code{unset} is not supported by all shells!
10983 Some ancient systems have quite
10984 small limits on the length of the @samp{#!} line; for instance, 32
10985 bytes (not including the newline) on SunOS 4.
10986 A few ancient 4.2@acronym{BSD} based systems (such as Dynix circa 1984)
10987 required a single space between the @samp{#!} and the @samp{/}.
10988 However, these ancient systems are no longer of practical concern.
10990 The set of external programs you should run in a @command{configure} script
10991 is fairly small. @xref{Utilities in Makefiles, , Utilities in
10992 Makefiles, standards, @acronym{GNU} Coding Standards}, for the list. This
10993 restriction allows users to start out with a fairly small set of
10994 programs and build the rest, avoiding too many interdependencies between
10997 Some of these external utilities have a portable subset of features; see
10998 @ref{Limitations of Usual Tools}.
11000 There are other sources of documentation about shells. The
11001 specification for the Posix
11002 @uref{http://www.opengroup.org/@/susv3/@/utilities/@/xcu_chap02.html, Shell
11003 Command Language}, though more generous than the restrictive shell
11004 subset described above, is fairly portable nowadays. Also please see
11005 @uref{http://www.faqs.org/@/faqs/@/unix-faq/@/shell/, the Shell FAQs}.
11008 * Shellology:: A zoology of shells
11009 * Here-Documents:: Quirks and tricks
11010 * File Descriptors:: FDs and redirections
11011 * File System Conventions:: File names
11012 * Shell Pattern Matching:: Pattern matching
11013 * Shell Substitutions:: Variable and command expansions
11014 * Assignments:: Varying side effects of assignments
11015 * Parentheses:: Parentheses in shell scripts
11016 * Slashes:: Slashes in shell scripts
11017 * Special Shell Variables:: Variables you should not change
11018 * Limitations of Builtins:: Portable use of not so portable /bin/sh
11019 * Limitations of Usual Tools:: Portable use of portable tools
11023 @section Shellology
11026 There are several families of shells, most prominently the Bourne family
11027 and the C shell family which are deeply incompatible. If you want to
11028 write portable shell scripts, avoid members of the C shell family. The
11029 @uref{http://www.faqs.org/@/faqs/@/unix-faq/@/shell/@/shell-differences/, the
11030 Shell difference FAQ} includes a small history of Posix shells, and a
11031 comparison between several of them.
11033 Below we describe some of the members of the Bourne shell family.
11038 Ash is often used on @acronym{GNU}/Linux and @acronym{BSD}
11039 systems as a light-weight Bourne-compatible shell. Ash 0.2 has some
11040 bugs that are fixed in the 0.3.x series, but portable shell scripts
11041 should work around them, since version 0.2 is still shipped with many
11042 @acronym{GNU}/Linux distributions.
11044 To be compatible with Ash 0.2:
11048 don't use @samp{$?} after expanding empty or unset variables,
11049 or at the start of an @command{eval}:
11055 echo "Do not use it: $?"
11057 eval 'echo "Do not use it: $?"'
11061 don't use command substitution within variable expansion:
11068 beware that single builtin substitutions are not performed by a
11069 subshell, hence their effect applies to the current shell! @xref{Shell
11070 Substitutions}, item ``Command Substitution''.
11075 To detect whether you are running Bash, test whether
11076 @code{BASH_VERSION} is set. To require
11077 Posix compatibility, run @samp{set -o posix}. @xref{Bash POSIX
11078 Mode, , Bash Posix Mode, bash, The @acronym{GNU} Bash Reference
11079 Manual}, for details.
11081 @item Bash 2.05 and later
11082 @cindex Bash 2.05 and later
11083 Versions 2.05 and later of Bash use a different format for the
11084 output of the @command{set} builtin, designed to make evaluating its
11085 output easier. However, this output is not compatible with earlier
11086 versions of Bash (or with many other shells, probably). So if
11087 you use Bash 2.05 or higher to execute @command{configure},
11088 you'll need to use Bash 2.05 for all other build tasks as well.
11093 @prindex @samp{ksh}
11094 @prindex @samp{ksh88}
11095 @prindex @samp{ksh93}
11096 The Korn shell is compatible with the Bourne family and it mostly
11097 conforms to Posix. It has two major variants commonly
11098 called @samp{ksh88} and @samp{ksh93}, named after the years of initial
11099 release. It is usually called @command{ksh}, but is called @command{sh}
11100 on some hosts if you set your path appropriately.
11102 Solaris systems have three variants:
11103 @prindex @command{/usr/bin/ksh} on Solaris
11104 @command{/usr/bin/ksh} is @samp{ksh88}; it is
11105 standard on Solaris 2.0 and later.
11106 @prindex @command{/usr/xpg4/bin/sh} on Solaris
11107 @command{/usr/xpg4/bin/sh} is a Posix-compliant variant of
11108 @samp{ksh88}; it is standard on Solaris 9 and later.
11109 @prindex @command{/usr/dt/bin/dtksh} on Solaris
11110 @command{/usr/dt/bin/dtksh} is @samp{ksh93}.
11111 Variants that are not standard may be parts of optional
11112 packages. There is no extra charge for these packages, but they are
11113 not part of a minimal OS install and therefore some installations may
11116 Starting with Tru64 Version 4.0, the Korn shell @command{/usr/bin/ksh}
11117 is also available as @command{/usr/bin/posix/sh}. If the environment
11118 variable @env{BIN_SH} is set to @code{xpg4}, subsidiary invocations of
11119 the standard shell conform to Posix.
11122 @prindex @samp{pdksh}
11123 A public-domain clone of the Korn shell called @command{pdksh} is widely
11124 available: it has most of the @samp{ksh88} features along with a few of
11125 its own. It usually sets @code{KSH_VERSION}, except if invoked as
11126 @command{/bin/sh} on Open@acronym{BSD}, and similarly to Bash you can require
11127 Posix compatibility by running @samp{set -o posix}. Unfortunately, with
11128 @command{pdksh} 5.2.14 (the latest stable version as of January 2007)
11129 Posix mode is buggy and causes @command{pdksh} to depart from Posix in
11130 at least one respect:
11133 $ @kbd{echo "`echo \"hello\"`"}
11135 $ @kbd{set -o posix}
11136 $ @kbd{echo "`echo \"hello\"`"}
11140 The last line of output contains spurious quotes. This is yet another
11141 reason why portable shell code should not contain
11142 @code{"`@dots{}\"@dots{}\"@dots{}`"} constructs (@pxref{Shell
11147 To detect whether you are running @command{zsh}, test whether
11148 @code{ZSH_VERSION} is set. By default @command{zsh} is @emph{not}
11149 compatible with the Bourne shell: you must execute @samp{emulate sh},
11150 and for @command{zsh} versions before 3.1.6-dev-18 you must also
11151 set @code{NULLCMD} to @samp{:}. @xref{Compatibility, , Compatibility,
11152 zsh, The Z Shell Manual}, for details.
11154 The default Mac OS X @command{sh} was originally Zsh; it was changed to
11155 Bash in Mac OS X 10.2.
11158 The following discussion between Russ Allbery and Robert Lipe is worth
11165 The @acronym{GNU} assumption that @command{/bin/sh} is the one and only shell
11166 leads to a permanent deadlock. Vendors don't want to break users'
11167 existing shell scripts, and there are some corner cases in the Bourne
11168 shell that are not completely compatible with a Posix shell. Thus,
11169 vendors who have taken this route will @emph{never} (OK@dots{}``never say
11170 never'') replace the Bourne shell (as @command{/bin/sh}) with a
11178 This is exactly the problem. While most (at least most System V's) do
11179 have a Bourne shell that accepts shell functions most vendor
11180 @command{/bin/sh} programs are not the Posix shell.
11182 So while most modern systems do have a shell @emph{somewhere} that meets the
11183 Posix standard, the challenge is to find it.
11186 @node Here-Documents
11187 @section Here-Documents
11188 @cindex Here-documents
11189 @cindex Shell here-documents
11191 Don't rely on @samp{\} being preserved just because it has no special
11192 meaning together with the next symbol. In the native @command{sh}
11193 on Open@acronym{BSD} 2.7 @samp{\"} expands to @samp{"} in here-documents with
11194 unquoted delimiter. As a general rule, if @samp{\\} expands to @samp{\}
11195 use @samp{\\} to get @samp{\}.
11197 With Open@acronym{BSD} 2.7's @command{sh}
11213 bash-2.04$ @kbd{cat <<EOF
11220 Some shells mishandle large here-documents: for example,
11221 Solaris 10 @command{dtksh} and the UnixWare 7.1.1 Posix shell, which are
11222 derived from Korn shell version M-12/28/93d, mishandle braced variable
11223 expansion that crosses a 1024- or 4096-byte buffer boundary
11224 within a here-document. Only the part of the variable name after the boundary
11225 is used. For example, @code{$@{variable@}} could be replaced by the expansion
11226 of @code{$@{ble@}}. If the end of the variable name is aligned with the block
11227 boundary, the shell reports an error, as if you used @code{$@{@}}.
11228 Instead of @code{$@{variable-default@}}, the shell may expand
11229 @code{$@{riable-default@}}, or even @code{$@{fault@}}. This bug can often
11230 be worked around by omitting the braces: @code{$variable}. The bug was fixed in
11231 @samp{ksh93g} (1998-04-30) but as of 2006 many operating systems were
11232 still shipping older versions with the bug.
11234 Many shells (including the Bourne shell) implement here-documents
11235 inefficiently. In particular, some shells can be extremely inefficient when
11236 a single statement contains many here-documents. For instance if your
11237 @file{configure.ac} includes something like:
11241 if <cross_compiling>; then
11242 assume this and that
11246 check something else
11254 A shell parses the whole @code{if}/@code{fi} construct, creating
11255 temporary files for each here-document in it. Some shells create links
11256 for such here-documents on every @code{fork}, so that the clean-up code
11257 they had installed correctly removes them. It is creating the links
11258 that can take the shell forever.
11260 Moving the tests out of the @code{if}/@code{fi}, or creating multiple
11261 @code{if}/@code{fi} constructs, would improve the performance
11262 significantly. Anyway, this kind of construct is not exactly the
11263 typical use of Autoconf. In fact, it's even not recommended, because M4
11264 macros can't look into shell conditionals, so we may fail to expand a
11265 macro when it was expanded before in a conditional path, and the
11266 condition turned out to be false at runtime, and we end up not
11267 executing the macro at all.
11269 @node File Descriptors
11270 @section File Descriptors
11271 @cindex Descriptors
11272 @cindex File descriptors
11273 @cindex Shell file descriptors
11275 Most shells, if not all (including Bash, Zsh, Ash), output traces on
11276 stderr, even for subshells. This might result in undesirable content
11277 if you meant to capture the standard-error output of the inner command:
11280 $ @kbd{ash -x -c '(eval "echo foo >&2") 2>stderr'}
11282 + eval echo foo >&2
11285 $ @kbd{bash -x -c '(eval "echo foo >&2") 2>stderr'}
11287 + eval 'echo foo >&2'
11290 $ @kbd{zsh -x -c '(eval "echo foo >&2") 2>stderr'}
11291 @i{# Traces on startup files deleted here.}
11293 +zsh:1> eval echo foo >&2
11299 One workaround is to grep out uninteresting lines, hoping not to remove
11302 If you intend to redirect both standard error and standard output,
11303 redirect standard output first. This works better with @acronym{HP-UX},
11304 since its shell mishandles tracing if standard error is redirected
11308 $ @kbd{sh -x -c ': 2>err >out'}
11310 + 2> err $ @kbd{cat err}
11314 Don't try to redirect the standard error of a command substitution. It
11315 must be done @emph{inside} the command substitution. When running
11316 @samp{: `cd /zorglub` 2>/dev/null} expect the error message to
11317 escape, while @samp{: `cd /zorglub 2>/dev/null`} works properly.
11319 It is worth noting that Zsh (but not Ash nor Bash) makes it possible
11320 in assignments though: @samp{foo=`cd /zorglub` 2>/dev/null}.
11322 Don't redirect the same file descriptor several times, as you are doomed
11323 to failure under Ultrix.
11326 ULTRIX V4.4 (Rev. 69) System #31: Thu Aug 10 19:42:23 GMT 1995
11328 $ @kbd{eval 'echo matter >fullness' >void}
11330 $ @kbd{eval '(echo matter >fullness)' >void}
11332 $ @kbd{(eval '(echo matter >fullness)') >void}
11333 Ambiguous output redirect.
11337 In each case the expected result is of course @file{fullness} containing
11338 @samp{matter} and @file{void} being empty.
11340 Don't rely on file descriptors 0, 1, and 2 remaining closed in a
11341 subsidiary program. If any of these descriptors is closed, the
11342 operating system may open an unspecified file for the descriptor in the
11343 new process image. Posix says this may be done only if the subsidiary
11344 program is set-user-ID or set-group-ID, but @acronym{HP-UX} 11.23 does it even for
11347 Don't rely on open file descriptors being open in child processes. In
11348 @command{ksh}, file descriptors above 2 which are opened using
11349 @samp{exec @var{n}>file} are closed by a subsequent @samp{exec} (such as
11350 that involved in the fork-and-exec which runs a program or script).
11351 Thus, using @command{sh}, we have:
11354 $ @kbd{cat ./descrips}
11376 Within the process which runs the @samp{descrips} script, file
11377 descriptor 5 is closed.
11379 @acronym{DOS} variants cannot rename or remove open files, such as in
11380 @samp{mv foo bar >foo} or @samp{rm foo >foo}, even though this is
11381 perfectly portable among Posix hosts.
11383 A few ancient systems reserved some file descriptors. By convention,
11384 file descriptor 3 was opened to @file{/dev/tty} when you logged into
11385 Eighth Edition (1985) through Tenth Edition Unix (1989). File
11386 descriptor 4 had a special use on the Stardent/Kubota Titan (circa
11387 1990), though we don't now remember what it was. Both these systems are
11388 obsolete, so it's now safe to treat file descriptors 3 and 4 like any
11389 other file descriptors.
11391 @node File System Conventions
11392 @section File System Conventions
11393 @cindex File system conventions
11395 Autoconf uses shell-script processing extensively, so the file names
11396 that it processes should not contain characters that are special to the
11397 shell. Special characters include space, tab, newline, @sc{nul}, and
11401 " # $ & ' ( ) * ; < = > ? [ \ ` |
11404 Also, file names should not begin with @samp{~} or @samp{-}, and should
11405 contain neither @samp{-} immediately after @samp{/} nor @samp{~}
11406 immediately after @samp{:}. On Posix-like platforms, directory names
11407 should not contain @samp{:}, as this runs afoul of @samp{:} used as the
11410 These restrictions apply not only to the files that you distribute, but
11411 also to the absolute file names of your source, build, and destination
11414 On some Posix-like platforms, @samp{!} and @samp{^} are special too, so
11415 they should be avoided.
11417 Posix lets implementations treat leading @file{//} specially, but
11418 requires leading @file{///} and beyond to be equivalent to @file{/}.
11419 Most Unix variants treat @file{//} like @file{/}. However, some treat
11420 @file{//} as a ``super-root'' that can provide access to files that are
11421 not otherwise reachable from @file{/}. The super-root tradition began
11422 with Apollo Domain/OS, which died out long ago, but unfortunately Cygwin
11425 While @command{autoconf} and friends are usually run on some Posix
11426 variety, they can be used on other systems, most notably @acronym{DOS}
11427 variants. This impacts several assumptions regarding file names.
11430 For example, the following code:
11437 foo_dir=$dots$foo_dir ;;
11442 fails to properly detect absolute file names on those systems, because
11443 they can use a drivespec, and usually use a backslash as directory
11444 separator. If you want to be portable to @acronym{DOS} variants (at the
11445 price of rejecting valid but oddball Posix file names like @file{a:\b}),
11446 you can check for absolute file names like this:
11450 [\\/]* | ?:[\\/]* ) # Absolute
11453 foo_dir=$dots$foo_dir ;;
11458 Make sure you quote the brackets if appropriate and keep the backslash as
11459 first character (@pxref{Limitations of Builtins}).
11461 Also, because the colon is used as part of a drivespec, these systems don't
11462 use it as path separator. When creating or accessing paths, you can use the
11463 @code{PATH_SEPARATOR} output variable instead. @command{configure} sets this
11464 to the appropriate value for the build system (@samp{:} or @samp{;}) when it
11467 File names need extra care as well. While @acronym{DOS} variants
11468 that are Posixy enough to run @command{autoconf} (such as @acronym{DJGPP})
11469 are usually able to handle long file names properly, there are still
11470 limitations that can seriously break packages. Several of these issues
11471 can be easily detected by the
11472 @uref{ftp://ftp.gnu.org/gnu/non-gnu/doschk/doschk-1.1.tar.gz, doschk}
11475 A short overview follows; problems are marked with @sc{sfn}/@sc{lfn} to
11476 indicate where they apply: @sc{sfn} means the issues are only relevant to
11477 plain @acronym{DOS}, not to @acronym{DOS} under Microsoft Windows
11478 variants, while @sc{lfn} identifies problems that exist even under
11479 Microsoft Windows variants.
11482 @item No multiple dots (@sc{sfn})
11483 @acronym{DOS} cannot handle multiple dots in file names. This is an especially
11484 important thing to remember when building a portable configure script,
11485 as @command{autoconf} uses a .in suffix for template files.
11487 This is perfectly OK on Posix variants:
11490 AC_CONFIG_HEADERS([config.h])
11491 AC_CONFIG_FILES([source.c foo.bar])
11496 but it causes problems on @acronym{DOS}, as it requires @samp{config.h.in},
11497 @samp{source.c.in} and @samp{foo.bar.in}. To make your package more portable
11498 to @acronym{DOS}-based environments, you should use this instead:
11501 AC_CONFIG_HEADERS([config.h:config.hin])
11502 AC_CONFIG_FILES([source.c:source.cin foo.bar:foobar.in])
11506 @item No leading dot (@sc{sfn})
11507 @acronym{DOS} cannot handle file names that start with a dot. This is usually
11508 not important for @command{autoconf}.
11510 @item Case insensitivity (@sc{lfn})
11511 @acronym{DOS} is case insensitive, so you cannot, for example, have both a
11512 file called @samp{INSTALL} and a directory called @samp{install}. This
11513 also affects @command{make}; if there's a file called @samp{INSTALL} in
11514 the directory, @samp{make install} does nothing (unless the
11515 @samp{install} target is marked as PHONY).
11517 @item The 8+3 limit (@sc{sfn})
11518 Because the @acronym{DOS} file system only stores the first 8 characters of
11519 the file name and the first 3 of the extension, those must be unique.
11520 That means that @file{foobar-part1.c}, @file{foobar-part2.c} and
11521 @file{foobar-prettybird.c} all resolve to the same file name
11522 (@file{FOOBAR-P.C}). The same goes for @file{foo.bar} and
11523 @file{foo.bartender}.
11525 The 8+3 limit is not usually a problem under Microsoft Windows, as it
11527 tails in the short version of file names to make them unique. However, a
11528 registry setting can turn this behavior off. While this makes it
11529 possible to share file trees containing long file names between @sc{sfn}
11530 and @sc{lfn} environments, it also means the above problem applies there
11533 @item Invalid characters (@sc{lfn})
11534 Some characters are invalid in @acronym{DOS} file names, and should therefore
11535 be avoided. In a @sc{lfn} environment, these are @samp{/}, @samp{\},
11536 @samp{?}, @samp{*}, @samp{:}, @samp{<}, @samp{>}, @samp{|} and @samp{"}.
11537 In a @sc{sfn} environment, other characters are also invalid. These
11538 include @samp{+}, @samp{,}, @samp{[} and @samp{]}.
11540 @item Invalid names (@sc{lfn})
11541 Some @acronym{DOS} file names are reserved, and cause problems if you
11542 try to use files with those names. These names include @file{CON},
11543 @file{AUX}, @file{COM1}, @file{COM2}, @file{COM3}, @file{COM4},
11544 @file{LPT1}, @file{LPT2}, @file{LPT3}, @file{NUL}, and @file{PRN}.
11545 File names are case insensitive, so even names like
11546 @file{aux/config.guess} are disallowed.
11550 @node Shell Pattern Matching
11551 @section Shell Pattern Matching
11552 @cindex Shell pattern matching
11554 Nowadays portable patterns can use negated character classes like
11555 @samp{[!-aeiou]}. The older syntax @samp{[^-aeiou]} is supported by
11556 some shells but not others; hence portable scripts should never use
11557 @samp{^} as the first character of a bracket pattern.
11559 Outside the C locale, patterns like @samp{[a-z]} are problematic since
11560 they may match characters that are not lower-case letters.
11562 @node Shell Substitutions
11563 @section Shell Substitutions
11564 @cindex Shell substitutions
11566 Contrary to a persistent urban legend, the Bourne shell does not
11567 systematically split variables and back-quoted expressions, in particular
11568 on the right-hand side of assignments and in the argument of @code{case}.
11569 For instance, the following code:
11572 case "$given_srcdir" in
11573 .) top_srcdir="`echo "$dots" | sed 's,/$,,'`" ;;
11574 *) top_srcdir="$dots$given_srcdir" ;;
11579 is more readable when written as:
11582 case $given_srcdir in
11583 .) top_srcdir=`echo "$dots" | sed 's,/$,,'` ;;
11584 *) top_srcdir=$dots$given_srcdir ;;
11589 and in fact it is even @emph{more} portable: in the first case of the
11590 first attempt, the computation of @code{top_srcdir} is not portable,
11591 since not all shells properly understand @code{"`@dots{}"@dots{}"@dots{}`"}.
11592 Worse yet, not all shells understand @code{"`@dots{}\"@dots{}\"@dots{}`"}
11593 the same way. There is just no portable way to use double-quoted
11594 strings inside double-quoted back-quoted expressions (pfew!).
11598 @cindex @samp{"$@@"}
11599 One of the most famous shell-portability issues is related to
11600 @samp{"$@@"}. When there are no positional arguments, Posix says
11601 that @samp{"$@@"} is supposed to be equivalent to nothing, but the
11602 original Unix version 7 Bourne shell treated it as equivalent to
11603 @samp{""} instead, and this behavior survives in later implementations
11604 like Digital Unix 5.0.
11606 The traditional way to work around this portability problem is to use
11607 @samp{$@{1+"$@@"@}}. Unfortunately this method does not work with
11608 Zsh (3.x and 4.x), which is used on Mac OS X@. When emulating
11609 the Bourne shell, Zsh performs word splitting on @samp{$@{1+"$@@"@}}:
11612 zsh $ @kbd{emulate sh}
11613 zsh $ @kbd{for i in "$@@"; do echo $i; done}
11616 zsh $ @kbd{for i in $@{1+"$@@"@}; do echo $i; done}
11623 Zsh handles plain @samp{"$@@"} properly, but we can't use plain
11624 @samp{"$@@"} because of the portability problems mentioned above.
11625 One workaround relies on Zsh's ``global aliases'' to convert
11626 @samp{$@{1+"$@@"@}} into @samp{"$@@"} by itself:
11629 test "$@{ZSH_VERSION+set@}" = set && alias -g '$@{1+"$@@"@}'='"$@@"'
11632 Zsh only recognizes this alias when a shell word matches it exactly;
11633 @samp{"foo"$@{1+"$@@"@}} remains subject to word splitting. Since this
11634 case always yields at least one shell word, use plain @samp{"$@@"}.
11636 A more conservative workaround is to avoid @samp{"$@@"} if it is
11637 possible that there may be no positional arguments. For example,
11641 cat conftest.c "$@@"
11644 you can use this instead:
11648 0) cat conftest.c;;
11649 *) cat conftest.c "$@@";;
11653 Autoconf macros often use the @command{set} command to update
11654 @samp{$@@}, so if you are writing shell code intended for
11655 @command{configure} you should not assume that the value of @samp{$@@}
11656 persists for any length of time.
11660 @cindex positional parameters
11661 The 10th, 11th, @dots{} positional parameters can be accessed only after
11662 a @code{shift}. The 7th Edition shell reported an error if given
11663 @code{$@{10@}}, and
11664 Solaris 10 @command{/bin/sh} still acts that way:
11667 $ @kbd{set 1 2 3 4 5 6 7 8 9 10}
11668 $ @kbd{echo $@{10@}}
11672 @item $@{@var{var}:-@var{value}@}
11673 @c Info cannot handle `:' in index entries.
11674 @c @cindex $@{@var{var}:-@var{value}@}
11675 Old @acronym{BSD} shells, including the Ultrix @code{sh}, don't accept the
11676 colon for any shell substitution, and complain and die.
11677 Similarly for $@{@var{var}:=@var{value}@}, $@{@var{var}:?@var{value}@}, etc.
11679 @item $@{@var{var}=@var{literal}@}
11680 @cindex $@{@var{var}=@var{literal}@}
11684 : $@{var='Some words'@}
11688 otherwise some shells, such as on Digital Unix V 5.0, die because
11689 of a ``bad substitution''.
11693 Solaris @command{/bin/sh} has a frightening bug in its interpretation
11694 of this. Imagine you need set a variable to a string containing
11695 @samp{@}}. This @samp{@}} character confuses Solaris @command{/bin/sh}
11696 when the affected variable was already set. This bug can be exercised
11701 $ @kbd{foo=$@{foo='@}'@}}
11704 $ @kbd{foo=$@{foo='@}' # no error; this hints to what the bug is}
11707 $ @kbd{foo=$@{foo='@}'@}}
11713 It seems that @samp{@}} is interpreted as matching @samp{$@{}, even
11714 though it is enclosed in single quotes. The problem doesn't happen
11715 using double quotes.
11717 @item $@{@var{var}=@var{expanded-value}@}
11718 @cindex $@{@var{var}=@var{expanded-value}@}
11724 : $@{var="$default"@}
11728 sets @var{var} to @samp{M-yM-uM-,M-yM-aM-a}, i.e., the 8th bit of
11729 each char is set. You don't observe the phenomenon using a simple
11730 @samp{echo $var} since apparently the shell resets the 8th bit when it
11731 expands $var. Here are two means to make this shell confess its sins:
11734 $ @kbd{cat -v <<EOF
11743 $ @kbd{set | grep '^var=' | cat -v}
11746 One classic incarnation of this bug is:
11750 : $@{list="$default"@}
11757 You'll get @samp{a b c} on a single line. Why? Because there are no
11758 spaces in @samp{$list}: there are @samp{M- }, i.e., spaces with the 8th
11759 bit set, hence no IFS splitting is performed!!!
11761 One piece of good news is that Ultrix works fine with @samp{:
11762 $@{list=$default@}}; i.e., if you @emph{don't} quote. The bad news is
11763 then that @acronym{QNX} 4.25 then sets @var{list} to the @emph{last} item of
11766 The portable way out consists in using a double assignment, to switch
11767 the 8th bit twice on Ultrix:
11770 list=$@{list="$default"@}
11774 @dots{}but beware of the @samp{@}} bug from Solaris (see above). For safety,
11778 test "$@{var+set@}" = set || var=@var{@{value@}}
11781 @item $@{#@var{var}@}
11782 @itemx $@{@var{var}%@var{word}@}
11783 @itemx $@{@var{var}%%@var{word}@}
11784 @itemx $@{@var{var}#@var{word}@}
11785 @itemx $@{@var{var}##@var{word}@}
11786 @cindex $@{#@var{var}@}
11787 @cindex $@{@var{var}%@var{word}@}
11788 @cindex $@{@var{var}%%@var{word}@}
11789 @cindex $@{@var{var}#@var{word}@}
11790 @cindex $@{@var{var}##@var{word}@}
11791 Posix requires support for these usages, but they do not work with many
11792 traditional shells, e.g., Solaris 10 @command{/bin/sh}.
11794 Also, @command{pdksh} 5.2.14 mishandles some @var{word} forms. For
11795 example if @samp{$1} is @samp{a/b} and @samp{$2} is @samp{a}, then
11796 @samp{$@{1#$2@}} should yield @samp{/b}, but with @command{pdksh} it
11797 yields the empty string.
11800 @item `@var{commands}`
11801 @cindex `@var{commands}`
11802 @cindex Command Substitution
11803 Posix requires shells to trim all trailing newlines from command
11804 output before substituting it, so assignments like
11805 @samp{dir=`echo "$file" | tr a A`} do not work as expected if
11806 @samp{$file} ends in a newline.
11808 While in general it makes no sense, do not substitute a single builtin
11809 with side effects, because Ash 0.2, trying to optimize, does not fork a
11810 subshell to perform the command.
11812 For instance, if you wanted to check that @command{cd} is silent, do not
11813 use @samp{test -z "`cd /`"} because the following can happen:
11818 $ @kbd{test -z "`cd /`" && pwd}
11823 The result of @samp{foo=`exit 1`} is left as an exercise to the reader.
11825 The MSYS shell leaves a stray byte in the expansion of a double-quoted
11826 command substitution of a native program, if the end of the substitution
11827 is not aligned with the end of the double quote. This may be worked
11828 around by inserting another pair of quotes:
11831 $ @kbd{echo "`printf 'foo\r\n'` bar" > broken}
11832 $ @kbd{echo "`printf 'foo\r\n'`"" bar" | cmp - broken}
11833 - broken differ: char 4, line 1
11837 @item $(@var{commands})
11838 @cindex $(@var{commands})
11839 This construct is meant to replace @samp{`@var{commands}`},
11840 and it has most of the problems listed under @code{`@var{commands}`}.
11842 This construct can be
11843 nested while this is impossible to do portably with back quotes.
11844 Unfortunately it is not yet universally supported. Most notably, even recent
11845 releases of Solaris don't support it:
11848 $ @kbd{showrev -c /bin/sh | grep version}
11849 Command version: SunOS 5.10 Generic 121005-03 Oct 2006
11850 $ @kbd{echo $(echo blah)}
11851 syntax error: `(' unexpected
11855 nor does @sc{irix} 6.5's Bourne shell:
11858 IRIX firebird-image 6.5 07151432 IP22
11859 $ @kbd{echo $(echo blah)}
11863 If you do use @samp{$(@var{commands})}, make sure that the commands
11864 do not start with a parenthesis, as that would cause confusion with
11865 a different notation @samp{$((@var{expression}))} that in modern
11866 shells is an arithmetic expression not a command. To avoid the
11867 confusion, insert a space between the two opening parentheses.
11869 Avoid @var{commands} that contain unbalanced parentheses in
11870 here-documents, comments, or case statement patterns, as many shells
11871 mishandle them. For example, Bash 3.1, @samp{ksh88}, @command{pdksh}
11872 5.2.14, and Zsh 4.2.6 all mishandle the following valid command:
11875 echo $(case x in x) echo hello;; esac)
11880 Always quote @samp{^}, otherwise traditional shells such as
11881 @command{/bin/sh} on Solaris 10 treat this like @samp{|}.
11887 @section Assignments
11888 @cindex Shell assignments
11890 When setting several variables in a row, be aware that the order of the
11891 evaluation is undefined. For instance @samp{foo=1 foo=2; echo $foo}
11892 gives @samp{1} with Solaris @command{/bin/sh}, but @samp{2} with Bash.
11894 @samp{;} to enforce the order: @samp{foo=1; foo=2; echo $foo}.
11896 Don't rely on the following to find @file{subdir/program}:
11899 PATH=subdir$PATH_SEPARATOR$PATH program
11903 as this does not work with Zsh 3.0.6. Use something like this
11907 (PATH=subdir$PATH_SEPARATOR$PATH; export PATH; exec program)
11910 Don't rely on the exit status of an assignment: Ash 0.2 does not change
11911 the status and propagates that of the last statement:
11914 $ @kbd{false || foo=bar; echo $?}
11916 $ @kbd{false || foo=`:`; echo $?}
11921 and to make things even worse, @acronym{QNX} 4.25 just sets the exit status
11925 $ @kbd{foo=`exit 1`; echo $?}
11929 To assign default values, follow this algorithm:
11933 If the default value is a literal and does not contain any closing
11937 : $@{var='my literal'@}
11941 If the default value contains no closing brace, has to be expanded, and
11942 the variable being initialized is not intended to be IFS-split
11943 (i.e., it's not a list), then use:
11946 : $@{var="$default"@}
11950 If the default value contains no closing brace, has to be expanded, and
11951 the variable being initialized is intended to be IFS-split (i.e., it's a list),
11955 var=$@{var="$default"@}
11959 If the default value contains a closing brace, then use:
11962 test "$@{var+set@}" = set || var="has a '@}'"
11966 In most cases @samp{var=$@{var="$default"@}} is fine, but in case of
11967 doubt, just use the last form. @xref{Shell Substitutions}, items
11968 @samp{$@{@var{var}:-@var{value}@}} and @samp{$@{@var{var}=@var{value}@}}
11972 @section Parentheses in Shell Scripts
11973 @cindex Shell parentheses
11975 Beware of two opening parentheses in a row, as many shell
11976 implementations treat them specially. Posix requires that the command
11977 @samp{((cat))} must behave like @samp{(cat)}, but many shells, including
11978 Bash and the Korn shell, treat @samp{((cat))} as an arithmetic
11979 expression equivalent to @samp{let "cat"}, and may or may not report an
11980 error when they detect that @samp{cat} is not a number. As another
11981 example, @samp{pdksh} 5.2.14 misparses the following code:
11984 if ((true) || false); then
11990 To work around this problem, insert a space between the two opening
11991 parentheses. There is a similar problem and workaround with
11992 @samp{$((}; see @ref{Shell Substitutions}.
11995 @section Slashes in Shell Scripts
11996 @cindex Shell slashes
11998 Unpatched Tru64 5.1 @command{sh} omits the last slash of command-line
11999 arguments that contain two trailing slashes:
12002 $ @kbd{echo / // /// //// .// //.}
12005 $ @kbd{eval "echo \$x"}
12008 $ @kbd{echo abc | tr -t ab //}
12014 Unpatched Tru64 4.0 @command{sh} adds a slash after @samp{"$var"} if the
12015 variable is empty and the second double-quote is followed by a word that
12016 begins and ends with slash:
12019 $ @kbd{sh -xc 'p=; echo "$p"/ouch/'}
12025 However, our understanding is that patches are available, so perhaps
12026 it's not worth worrying about working around these horrendous bugs.
12028 @node Special Shell Variables
12029 @section Special Shell Variables
12030 @cindex Shell variables
12031 @cindex Special shell variables
12033 Some shell variables should not be used, since they can have a deep
12034 influence on the behavior of the shell. In order to recover a sane
12035 behavior from the shell, some variables should be unset, but
12036 @command{unset} is not portable (@pxref{Limitations of Builtins}) and a
12037 fallback value is needed.
12039 As a general rule, shell variable names containing a lower-case letter
12040 are safe; you can define and use these variables without worrying about
12041 their effect on the underlying system, and without worrying about
12042 whether the shell changes them unexpectedly. (The exception is the
12043 shell variable @code{status}, as described below.)
12045 Here is a list of names that are known to cause trouble. This list is
12046 not exhaustive, but you should be safe if you avoid the name
12047 @code{status} and names containing only upper-case letters and
12050 @c Alphabetical order, case insensitive, `A' before `a'.
12053 Many shells reserve @samp{$_} for various purposes, e.g., the name of
12054 the last command executed.
12058 In Tru64, if @env{BIN_SH} is set to @code{xpg4}, subsidiary invocations of
12059 the standard shell conform to Posix.
12063 When this variable is set it specifies a list of directories to search
12064 when invoking @code{cd} with a relative file name that did not start
12065 with @samp{./} or @samp{../}. Posix
12066 1003.1-2001 says that if a nonempty directory name from @env{CDPATH}
12067 is used successfully, @code{cd} prints the resulting absolute
12068 file name. Unfortunately this output can break idioms like
12069 @samp{abs=`cd src && pwd`} because @code{abs} receives the name twice.
12070 Also, many shells do not conform to this part of Posix; for
12071 example, @command{zsh} prints the result only if a directory name
12072 other than @file{.} was chosen from @env{CDPATH}.
12074 In practice the shells that have this problem also support
12075 @command{unset}, so you can work around the problem as follows:
12078 (unset CDPATH) >/dev/null 2>&1 && unset CDPATH
12081 You can also avoid output by ensuring that your directory name is
12082 absolute or anchored at @samp{./}, as in @samp{abs=`cd ./src && pwd`}.
12084 Autoconf-generated scripts automatically unset @env{CDPATH} if
12085 possible, so you need not worry about this problem in those scripts.
12089 In the MKS shell, case statements and file name generation are
12090 case-insensitive unless @env{DUALCASE} is nonzero.
12091 Autoconf-generated scripts export this variable when they start up.
12105 These variables should not matter for shell scripts, since they are
12106 supposed to affect only interactive shells. However, at least one
12107 shell (the pre-3.0 @sc{uwin} Korn shell) gets confused about
12108 whether it is interactive, which means that (for example) a @env{PS1}
12109 with a side effect can unexpectedly modify @samp{$?}. To work around
12110 this bug, Autoconf-generated scripts do something like this:
12113 (unset ENV) >/dev/null 2>&1 && unset ENV MAIL MAILPATH
12121 Long ago, shell scripts inherited @env{IFS} from the environment,
12122 but this caused many problems so modern shells ignore any environment
12123 settings for @env{IFS}.
12125 Don't set the first character of @code{IFS} to backslash. Indeed,
12126 Bourne shells use the first character (backslash) when joining the
12127 components in @samp{"$@@"} and some shells then reinterpret (!)@: the
12128 backslash escapes, so you can end up with backspace and other strange
12131 The proper value for @code{IFS} (in regular code, not when performing
12132 splits) is @samp{@key{SPC}@key{TAB}@key{RET}}. The first character is
12133 especially important, as it is used to join the arguments in @samp{$*};
12134 however, note that traditional shells, but also bash-2.04, fail to adhere
12135 to this and join with a space anyway.
12147 @evindex LC_COLLATE
12149 @evindex LC_MESSAGES
12150 @evindex LC_MONETARY
12151 @evindex LC_NUMERIC
12154 Autoconf-generated scripts normally set all these variables to
12155 @samp{C} because so much configuration code assumes the C locale and
12156 Posix requires that locale environment variables be set to
12157 @samp{C} if the C locale is desired. However, some older, nonstandard
12158 systems (notably @acronym{SCO}) break if locale environment variables
12159 are set to @samp{C}, so when running on these systems
12160 Autoconf-generated scripts unset the variables instead.
12165 @env{LANGUAGE} is not specified by Posix, but it is a @acronym{GNU}
12166 extension that overrides @env{LC_ALL} in some cases, so
12167 Autoconf-generated scripts set it too.
12170 @itemx LC_IDENTIFICATION
12171 @itemx LC_MEASUREMENT
12174 @itemx LC_TELEPHONE
12175 @evindex LC_ADDRESS
12176 @evindex LC_IDENTIFICATION
12177 @evindex LC_MEASUREMENT
12180 @evindex LC_TELEPHONE
12182 These locale environment variables are @acronym{GNU} extensions. They
12183 are treated like their Posix brethren (@env{LC_COLLATE},
12184 etc.)@: as described above.
12187 Most modern shells provide the current line number in @code{LINENO}.
12188 Its value is the line number of the beginning of the current command.
12189 Autoconf attempts to execute @command{configure} with a shell that
12190 supports @code{LINENO}.
12191 If no such shell is available, it attempts to implement @code{LINENO}
12192 with a Sed prepass that replaces each instance of the string
12193 @code{$LINENO} (not followed by an alphanumeric character) with the
12196 You should not rely on @code{LINENO} within @command{eval}, as the
12197 behavior differs in practice. Also, the possibility of the Sed
12198 prepass means that you should not rely on @code{$LINENO} when quoted,
12199 when in here-documents, or when in long commands that cross line
12200 boundaries. Subshells should be OK, though. In the following
12201 example, lines 1, 6, and 9 are portable, but the other instances of
12202 @code{LINENO} are not:
12212 ( echo 6. $LINENO )
12213 eval 'echo 7. $LINENO'
12219 $ @kbd{bash-2.05 lineno}
12230 $ @kbd{zsh-3.0.6 lineno}
12241 $ @kbd{pdksh-5.2.14 lineno}
12252 $ @kbd{sed '=' <lineno |}
12258 > @kbd{ s,^\([0-9]*\)\(.*\)[$]LINENO\([^a-zA-Z0-9_]\),\1\2\1\3,}
12261 > @kbd{ s,^[0-9]*\n,,}
12277 When executing the command @samp{>foo}, @command{zsh} executes
12278 @samp{$NULLCMD >foo} unless it is operating in Bourne shell
12279 compatibility mode and the @command{zsh} version is newer
12280 than 3.1.6-dev-18. If you are using an older @command{zsh}
12281 and forget to set @env{NULLCMD},
12282 your script might be suspended waiting for data on its standard input.
12284 @item PATH_SEPARATOR
12285 @evindex PATH_SEPARATOR
12286 On @acronym{DJGPP} systems, the @env{PATH_SEPARATOR} environment
12287 variable can be set to either @samp{:} or @samp{;} to control the path
12288 separator Bash uses to set up certain environment variables (such as
12289 @env{PATH}). You can set this variable to @samp{;} if you want
12290 @command{configure} to use @samp{;} as a separator; this might be useful
12291 if you plan to use non-Posix shells to execute files. @xref{File System
12292 Conventions}, for more information about @code{PATH_SEPARATOR}.
12296 Posix 1003.1-2001 requires that @command{cd} and
12297 @command{pwd} must update the @env{PWD} environment variable to point
12298 to the logical name of the current directory, but traditional shells
12299 do not support this. This can cause confusion if one shell instance
12300 maintains @env{PWD} but a subsidiary and different shell does not know
12301 about @env{PWD} and executes @command{cd}; in this case @env{PWD}
12302 points to the wrong directory. Use @samp{`pwd`} rather than
12306 Many shells provide @code{RANDOM}, a variable that returns a different
12307 integer each time it is used. Most of the time, its value does not
12308 change when it is not used, but on @sc{irix} 6.5 the value changes all
12309 the time. This can be observed by using @command{set}. It is common
12310 practice to use @code{$RANDOM} as part of a file name, but code
12311 shouldn't rely on @code{$RANDOM} expanding to a nonempty string.
12314 This variable is an alias to @samp{$?} for @code{zsh} (at least 3.1.6),
12315 hence read-only. Do not use it.
12318 @node Limitations of Builtins
12319 @section Limitations of Shell Builtins
12320 @cindex Shell builtins
12321 @cindex Limitations of shell builtins
12323 No, no, we are serious: some shells do have limitations! :)
12325 You should always keep in mind that any builtin or command may support
12326 options, and therefore differ in behavior with arguments
12327 starting with a dash. For instance, the innocent @samp{echo "$word"}
12328 can give unexpected results when @code{word} starts with a dash. It is
12329 often possible to avoid this problem using @samp{echo "x$word"}, taking
12330 the @samp{x} into account later in the pipe.
12334 @prindex @command{.}
12335 Use @command{.} only with regular files (use @samp{test -f}). Bash
12336 2.03, for instance, chokes on @samp{. /dev/null}. Also, remember that
12337 @command{.} uses @env{PATH} if its argument contains no slashes, so if
12338 you want to use @command{.} on a file @file{foo} in the current
12339 directory, you must use @samp{. ./foo}.
12342 @prindex @command{!}
12343 The Unix version 7 shell did not support
12344 negating the exit status of commands with @command{!}, and this feature
12345 is still absent from some shells (e.g., Solaris @command{/bin/sh}).
12346 Shell code like this:
12349 if ! cmp file1 file2 >/dev/null 2>&1; then
12350 echo files differ or trouble
12354 is therefore not portable in practice. Typically it is easy to rewrite
12358 cmp file1 file2 >/dev/null 2>&1 ||
12359 echo files differ or trouble
12362 More generally, one can always rewrite @samp{! @var{command}} as:
12365 if @var{command}; then (exit 1); else :; fi
12368 @item @command{break}
12369 @c ------------------
12370 @prindex @command{break}
12371 The use of @samp{break 2} etc.@: is safe.
12374 @item @command{case}
12375 @c -----------------
12376 @prindex @command{case}
12377 You don't need to quote the argument; no splitting is performed.
12379 You don't need the final @samp{;;}, but you should use it.
12381 Posix requires support for @code{case} patterns with opening
12382 parentheses like this:
12386 (*.c) echo "C source code";;
12391 but the @code{(} in this example is not portable to many Bourne
12392 shell implementations. It can be omitted safely.
12394 Zsh handles pattern fragments derived from parameter expansions or
12395 command substitutions as though quoted:
12398 $ pat=\?; case aa in ?$pat) echo match;; esac
12399 $ pat=\?; case a? in ?$pat) echo match;; esac
12404 Because of a bug in its @code{fnmatch}, Bash fails to properly
12405 handle backslashes in character classes:
12408 bash-2.02$ @kbd{case /tmp in [/\\]*) echo OK;; esac}
12413 This is extremely unfortunate, since you are likely to use this code to
12414 handle Posix or @sc{ms-dos} absolute file names. To work around this
12415 bug, always put the backslash first:
12418 bash-2.02$ @kbd{case '\TMP' in [\\/]*) echo OK;; esac}
12420 bash-2.02$ @kbd{case /tmp in [\\/]*) echo OK;; esac}
12424 Many Bourne shells cannot handle closing brackets in character classes
12427 Some shells also have problems with backslash escaping in case you do not want
12428 to match the backslash: both a backslash and the escaped character match this
12429 pattern. To work around this, specify the character class in a variable, so
12430 that quote removal does not apply afterwards, and the special characters don't
12431 have to be backslash-escaped:
12434 $ @kbd{case '\' in [\<]) echo OK;; esac}
12436 $ @kbd{scanset='[<]'; case '\' in $scanset) echo OK;; esac}
12440 Even with this, Solaris @command{ksh} matches a backslash if the set
12442 of the characters @samp{|}, @samp{&}, @samp{(}, or @samp{)}.
12444 Conversely, Tru64 @command{ksh} (circa 2003) erroneously always matches
12445 a closing parenthesis if not specified in a character class:
12448 $ @kbd{case foo in *\)*) echo fail ;; esac}
12450 $ @kbd{case foo in *')'*) echo fail ;; esac}
12454 Some shells, such as Ash 0.3.8, are confused by an empty
12455 @code{case}/@code{esac}:
12458 ash-0.3.8 $ @kbd{case foo in esac;}
12459 @error{}Syntax error: ";" unexpected (expecting ")")
12462 Many shells still do not support parenthesized cases, which is a pity
12463 for those of us using tools that rely on balanced parentheses. For
12464 instance, Solaris @command{/bin/sh}:
12467 $ @kbd{case foo in (foo) echo foo;; esac}
12468 @error{}syntax error: `(' unexpected
12474 @prindex @command{cd}
12475 Posix 1003.1-2001 requires that @command{cd} must support
12476 the @option{-L} (``logical'') and @option{-P} (``physical'') options,
12477 with @option{-L} being the default. However, traditional shells do
12478 not support these options, and their @command{cd} command has the
12479 @option{-P} behavior.
12481 Portable scripts should assume neither option is supported, and should
12482 assume neither behavior is the default. This can be a bit tricky,
12483 since the Posix default behavior means that, for example,
12484 @samp{ls ..} and @samp{cd ..} may refer to different directories if
12485 the current logical directory is a symbolic link. It is safe to use
12486 @command{cd @var{dir}} if @var{dir} contains no @file{..} components.
12487 Also, Autoconf-generated scripts check for this problem when computing
12488 variables like @code{ac_top_srcdir} (@pxref{Configuration Actions}),
12489 so it is safe to @command{cd} to these variables.
12491 See @xref{Special Shell Variables}, for portability problems involving
12492 @command{cd} and the @env{CDPATH} environment variable.
12493 Also please see the discussion of the @command{pwd} command.
12496 @item @command{echo}
12497 @c -----------------
12498 @prindex @command{echo}
12499 The simple @command{echo} is probably the most surprising source of
12500 portability troubles. It is not possible to use @samp{echo} portably
12501 unless both options and escape sequences are omitted. New applications
12502 which are not aiming at portability should use @samp{printf} instead of
12505 Don't expect any option. @xref{Preset Output Variables}, @code{ECHO_N}
12506 etc.@: for a means to simulate @option{-n}.
12508 Do not use backslashes in the arguments, as there is no consensus on
12509 their handling. For @samp{echo '\n' | wc -l}, the @command{sh} of
12510 Solaris outputs 2, but Bash and Zsh (in @command{sh} emulation mode) output 1.
12511 The problem is truly @command{echo}: all the shells
12512 understand @samp{'\n'} as the string composed of a backslash and an
12515 Because of these problems, do not pass a string containing arbitrary
12516 characters to @command{echo}. For example, @samp{echo "$foo"} is safe
12517 if you know that @var{foo}'s value cannot contain backslashes and cannot
12518 start with @samp{-}, but otherwise you should use a here-document like
12528 @item @command{eval}
12529 @c -----------------
12530 @prindex @command{eval}
12531 The @command{eval} command is useful in limited circumstances, e.g.,
12532 using commands like @samp{eval table_$key=\$value} and @samp{eval
12533 value=table_$key} to simulate a hash table when the key is known to be
12534 alphanumeric. However, @command{eval} is tricky to use on arbitrary
12535 arguments, even when it is implemented correctly.
12537 It is obviously unwise to use @samp{eval $cmd} if the string value of
12538 @samp{cmd} was derived from an untrustworthy source. But even if the
12539 string value is valid, @samp{eval $cmd} might not work as intended,
12540 since it causes field splitting and file name expansion to occur twice,
12541 once for the @command{eval} and once for the command itself. It is
12542 therefore safer to use @samp{eval "$cmd"}. For example, if @var{cmd}
12543 has the value @samp{cat test?.c}, @samp{eval $cmd} might expand to the
12544 equivalent of @samp{cat test;.c} if there happens to be a file named
12545 @file{test;.c} in the current directory; and this in turn
12546 mistakenly attempts to invoke @command{cat} on the file @file{test} and
12547 then execute the command @command{.c}. To avoid this problem, use
12548 @samp{eval "$cmd"} rather than @samp{eval $cmd}.
12550 However, suppose that you want to output the text of the evaluated
12551 command just before executing it. Assuming the previous example,
12552 @samp{echo "Executing: $cmd"} outputs @samp{Executing: cat test?.c}, but
12553 this output doesn't show the user that @samp{test;.c} is the actual name
12554 of the copied file. Conversely, @samp{eval "echo Executing: $cmd"}
12555 works on this example, but it fails with @samp{cmd='cat foo >bar'},
12556 since it mistakenly replaces the contents of @file{bar} by the
12557 string @samp{cat foo}. No simple, general, and portable solution to
12558 this problem is known.
12560 You should also be wary of common bugs in @command{eval} implementations.
12561 In some shell implementations (e.g., older @command{ash}, Open@acronym{BSD} 3.8
12562 @command{sh}, @command{pdksh} v5.2.14 99/07/13.2, and @command{zsh}
12563 4.2.5), the arguments of @samp{eval} are evaluated in a context where
12564 @samp{$?} is 0, so they exhibit behavior like this:
12567 $ @kbd{false; eval 'echo $?'}
12571 The correct behavior here is to output a nonzero value,
12572 but portable scripts should not rely on this.
12574 You should not rely on @code{LINENO} within @command{eval}.
12575 @xref{Special Shell Variables}.
12577 @item @command{exit}
12578 @c -----------------
12579 @prindex @command{exit}
12580 The default value of @command{exit} is supposed to be @code{$?};
12581 unfortunately, some shells, such as the @acronym{DJGPP} port of Bash 2.04, just
12582 perform @samp{exit 0}.
12585 bash-2.04$ @kbd{foo=`exit 1` || echo fail}
12587 bash-2.04$ @kbd{foo=`(exit 1)` || echo fail}
12589 bash-2.04$ @kbd{foo=`(exit 1); exit` || echo fail}
12593 Using @samp{exit $?} restores the expected behavior.
12595 Some shell scripts, such as those generated by @command{autoconf}, use a
12596 trap to clean up before exiting. If the last shell command exited with
12597 nonzero status, the trap also exits with nonzero status so that the
12598 invoker can tell that an error occurred.
12600 Unfortunately, in some shells, such as Solaris @command{/bin/sh}, an exit
12601 trap ignores the @code{exit} command's argument. In these shells, a trap
12602 cannot determine whether it was invoked by plain @code{exit} or by
12603 @code{exit 1}. Instead of calling @code{exit} directly, use the
12604 @code{AC_MSG_ERROR} macro that has a workaround for this problem.
12607 @item @command{export}
12608 @c -------------------
12609 @prindex @command{export}
12610 The builtin @command{export} dubs a shell variable @dfn{environment
12611 variable}. Each update of exported variables corresponds to an update
12612 of the environment variables. Conversely, each environment variable
12613 received by the shell when it is launched should be imported as a shell
12614 variable marked as exported.
12616 Alas, many shells, such as Solaris @command{/bin/sh},
12617 @sc{irix} 6.3, @sc{irix} 5.2,
12618 @acronym{AIX} 4.1.5, and Digital Unix 4.0, forget to
12619 @command{export} the environment variables they receive. As a result,
12620 two variables coexist: the environment variable and the shell
12621 variable. The following code demonstrates this failure:
12632 when run with @samp{FOO=foo} in the environment, these shells print
12633 alternately @samp{foo} and @samp{bar}, although they should print only
12634 @samp{foo} and then a sequence of @samp{bar}s.
12636 Therefore you should @command{export} again each environment variable
12640 @item @command{false}
12641 @c ------------------
12642 @prindex @command{false}
12643 Don't expect @command{false} to exit with status 1: in native
12644 Solaris @file{/bin/false} exits with status 255.
12647 @item @command{for}
12648 @c ----------------
12649 @prindex @command{for}
12650 To loop over positional arguments, use:
12660 You may @emph{not} leave the @code{do} on the same line as @code{for},
12661 since some shells improperly grok:
12669 If you want to explicitly refer to the positional arguments, given the
12670 @samp{$@@} bug (@pxref{Shell Substitutions}), use:
12673 for arg in $@{1+"$@@"@}; do
12679 But keep in mind that Zsh, even in Bourne shell emulation mode, performs
12680 word splitting on @samp{$@{1+"$@@"@}}; see @ref{Shell Substitutions},
12681 item @samp{$@@}, for more.
12686 @prindex @command{if}
12687 Using @samp{!} is not portable. Instead of:
12690 if ! cmp -s file file.new; then
12699 if cmp -s file file.new; then :; else
12704 There are shells that do not reset the exit status from an @command{if}:
12707 $ @kbd{if (exit 42); then true; fi; echo $?}
12712 whereas a proper shell should have printed @samp{0}. This is especially
12713 bad in makefiles since it produces false failures. This is why properly
12714 written makefiles, such as Automake's, have such hairy constructs:
12717 if test -f "$file"; then
12718 install "$file" "$dest"
12725 @item @command{printf}
12726 @c ------------------
12727 @prindex @command{printf}
12728 A format string starting with a @samp{-} can cause problems.
12729 Bash interprets it as an option and
12730 gives an error. And @samp{--} to mark the end of options is not good
12731 in the Net@acronym{BSD} Almquist shell (e.g., 0.4.6) which takes that
12732 literally as the format string. Putting the @samp{-} in a @samp{%c}
12733 or @samp{%s} is probably easiest:
12739 Bash 2.03 mishandles an escape sequence that happens to evaluate to @samp{%}:
12742 $ @kbd{printf '\045'}
12743 bash: printf: `%': missing format character
12746 Large outputs may cause trouble. On Solaris 2.5.1 through 10, for
12747 example, @file{/usr/bin/printf} is buggy, so when using
12748 @command{/bin/sh} the command @samp{printf %010000x 123} normally dumps
12752 @item @command{read}
12753 @c ------------------
12754 @prindex @command{read}
12755 Not all shells support @option{-r} (Solaris @command{/bin/sh} for example).
12758 @item @command{pwd}
12759 @c ----------------
12760 @prindex @command{pwd}
12761 With modern shells, plain @command{pwd} outputs a ``logical''
12762 directory name, some of whose components may be symbolic links. These
12763 directory names are in contrast to ``physical'' directory names, whose
12764 components are all directories.
12766 Posix 1003.1-2001 requires that @command{pwd} must support
12767 the @option{-L} (``logical'') and @option{-P} (``physical'') options,
12768 with @option{-L} being the default. However, traditional shells do
12769 not support these options, and their @command{pwd} command has the
12770 @option{-P} behavior.
12772 Portable scripts should assume neither option is supported, and should
12773 assume neither behavior is the default. Also, on many hosts
12774 @samp{/bin/pwd} is equivalent to @samp{pwd -P}, but Posix
12775 does not require this behavior and portable scripts should not rely on
12778 Typically it's best to use plain @command{pwd}. On modern hosts this
12779 outputs logical directory names, which have the following advantages:
12783 Logical names are what the user specified.
12785 Physical names may not be portable from one installation
12786 host to another due to network file system gymnastics.
12788 On modern hosts @samp{pwd -P} may fail due to lack of permissions to
12789 some parent directory, but plain @command{pwd} cannot fail for this
12793 Also please see the discussion of the @command{cd} command.
12796 @item @command{set}
12797 @c ----------------
12798 @prindex @command{set}
12799 With the Free@acronym{BSD} 6.0 shell, the @command{set} command (without
12800 any options) does not sort its output.
12802 The @command{set} builtin faces the usual problem with arguments starting with a
12803 dash. Modern shells such as Bash or Zsh understand @option{--} to specify
12804 the end of the options (any argument after @option{--} is a parameter,
12805 even @samp{-x} for instance), but many traditional shells (e.g., Solaris
12806 10 @command{/bin/sh}) simply stop option
12807 processing as soon as a non-option argument is found. Therefore, use
12808 @samp{dummy} or simply @samp{x} to end the option processing, and use
12809 @command{shift} to pop it out:
12812 set x $my_list; shift
12815 Avoid @samp{set -}, e.g., @samp{set - $my_list}. Posix no
12816 longer requires support for this command, and in traditional shells
12817 @samp{set - $my_list} resets the @option{-v} and @option{-x} options, which
12818 makes scripts harder to debug.
12820 Some nonstandard shells do not recognize more than one option
12821 (e.g., @samp{set -e -x} assigns @samp{-x} to the command line). It is
12822 better to combine them:
12828 The @acronym{BSD} shell has had several problems with the @option{-e}
12829 option, partly because @acronym{BSD} @command{make} traditionally used
12830 @option{-e} even though this was incompatible with Posix
12831 (@pxref{Failure in Make Rules}). Older versions of the @acronym{BSD}
12832 shell (circa 1990) mishandled @samp{&&}, @samp{||}, @samp{if}, and
12833 @samp{case} when @option{-e} was in effect, causing the shell to exit
12834 unexpectedly in some cases. This was particularly a problem with
12835 makefiles, and led to circumlocutions like @samp{sh -c 'test -f file ||
12836 touch file'}, where the seemingly-unnecessary @samp{sh -c '@dots{}'}
12837 wrapper works around the bug.
12839 Even relatively-recent versions of the @acronym{BSD} shell (e.g.,
12840 Open@acronym{BSD} 3.4) wrongly exit with @option{-e} if a command within
12841 @samp{&&} fails inside a compound statement. For example:
12847 test -n "$foo" && exit 1
12850 test -n "$foo" && exit 1
12856 does not print @samp{two}. One workaround is to use @samp{if test -n
12857 "$foo"; then exit 1; fi} rather than @samp{test -n "$foo" && exit 1}.
12858 Another possibility is to warn @acronym{BSD} users not to use @samp{sh -e}.
12861 @item @command{shift}
12862 @c ------------------
12863 @prindex @command{shift}
12864 Not only is @command{shift}ing a bad idea when there is nothing left to
12865 shift, but in addition it is not portable: the shell of @acronym{MIPS
12866 RISC/OS} 4.52 refuses to do it.
12868 Don't use @samp{shift 2} etc.; it was not in the 7th Edition Bourne shell,
12869 and it is also absent in many pre-Posix shells.
12872 @item @command{source}
12873 @c -------------------
12874 @prindex @command{source}
12875 This command is not portable, as Posix does not require it; use
12876 @command{.} instead.
12879 @item @command{test}
12880 @c -----------------
12881 @prindex @command{test}
12882 The @code{test} program is the way to perform many file and string
12883 tests. It is often invoked by the alternate name @samp{[}, but using
12884 that name in Autoconf code is asking for trouble since it is an M4 quote
12887 The @option{-a}, @option{-o}, @samp{(}, and @samp{)} operands are not
12888 portable and should be avoided. Thus, portable uses of @command{test}
12889 should never have more than four arguments, and scripts should use shell
12890 constructs like @samp{&&} and @samp{||} instead. If you combine
12891 @samp{&&} and @samp{||} in the same statement, keep in mind that they
12892 have equal precedence, so it is often better to parenthesize even when
12893 this is redundant. For example:
12897 test "X$a" = "X$b" -a \
12898 '(' "X$c" != "X$d" -o "X$e" = "X$f" ')'
12901 test "X$a" = "X$b" &&
12902 @{ test "X$c" != "X$d" || test "X$e" = "X$f"; @}
12905 @command{test} does not process options like most other commands do; for
12906 example, it does not recognize the @option{--} argument as marking the
12909 It is safe to use @samp{!} as a @command{test} operator. For example,
12910 @samp{if test ! -d foo; @dots{}} is portable even though @samp{if ! test
12911 -d foo; @dots{}} is not.
12914 @item @command{test} (files)
12915 @c -------------------------
12916 To enable @command{configure} scripts to support cross-compilation, they
12917 shouldn't do anything that tests features of the build system instead of
12918 the host system. But occasionally you may find it necessary to check
12919 whether some arbitrary file exists. To do so, use @samp{test -f} or
12920 @samp{test -r}. Do not use @samp{test -x}, because 4.3@acronym{BSD} does not
12921 have it. Do not use @samp{test -e} either, because Solaris @command{/bin/sh}
12922 lacks it. To test for symbolic links on systems that have them, use
12923 @samp{test -h} rather than @samp{test -L}; either form conforms to
12924 Posix 1003.1-2001, but older shells like Solaris 8
12925 @code{/bin/sh} support only @option{-h}.
12927 @item @command{test} (strings)
12928 @c ---------------------------
12929 Posix says that @samp{test "@var{string}"} succeeds if @var{string} is
12930 not null, but this usage is not portable to traditional platforms like
12931 Solaris 10 @command{/bin/sh}, which mishandle strings like @samp{!} and
12934 Posix says that @samp{test ! "@var{string}"}, @samp{test -n "@var{string}"} and
12935 @samp{test -z "@var{string}"} work with any string, but many
12936 shells (such as Solaris, @acronym{AIX} 3.2, @sc{unicos} 10.0.0.6,
12937 Digital Unix 4, etc.)@: get confused if
12938 @var{string} looks like an operator:
12942 test: argument expected
12944 test: argument expected
12947 Similarly, Posix says that @samp{test "@var{string1}" = "@var{string2"}}
12948 and @samp{test "@var{string1}" != "@var{string2"}} work for any pairs of
12949 strings, but in practice this is not true for troublesome strings that
12950 look like operators or parentheses, or that begin with @samp{-}.
12952 It is best to protect such strings with a leading @samp{X}, e.g.,
12953 @samp{test "X@var{string}" != X} rather than @samp{test -n
12954 "@var{string}"} or @samp{test ! "@var{string}"}.
12956 It is common to find variations of the following idiom:
12959 test -n "`echo $ac_feature | sed 's/[-a-zA-Z0-9_]//g'`" &&
12964 to take an action when a token matches a given pattern. Such constructs
12965 should be avoided by using:
12968 case $ac_feature in
12969 *[!-a-zA-Z0-9_]*) @var{action};;
12973 If the pattern is a complicated regular expression that cannot be
12974 expressed as a shell pattern, use something like this instead:
12977 expr "X$ac_feature" : 'X.*[^-a-zA-Z0-9_]' >/dev/null &&
12981 @samp{expr "X@var{foo}" : "X@var{bar}"} is more robust than @samp{echo
12982 "X@var{foo}" | grep "^X@var{bar}"}, because it avoids problems when
12983 @samp{@var{foo}} contains backslashes.
12986 @item @command{trap}
12987 @c -----------------
12988 @prindex @command{trap}
12989 It is safe to trap at least the signals 1, 2, 13, and 15. You can also
12990 trap 0, i.e., have the @command{trap} run when the script ends (either via an
12991 explicit @command{exit}, or the end of the script). The trap for 0 should be
12992 installed outside of a shell function, or @acronym{AIX} 5.3 @command{/bin/sh}
12993 will invoke the trap at the end of this function.
12995 Posix says that @samp{trap - 1 2 13 15} resets the traps for the
12996 specified signals to their default values, but many common shells (e.g.,
12997 Solaris @command{/bin/sh}) misinterpret this and attempt to execute a
12998 ``command'' named @command{-} when the specified conditions arise.
12999 There is no portable workaround, except for @samp{trap - 0}, for which
13000 @samp{trap '' 0} is a portable substitute.
13002 Although Posix is not absolutely clear on this point, it is widely
13003 admitted that when entering the trap @samp{$?} should be set to the exit
13004 status of the last command run before the trap. The ambiguity can be
13005 summarized as: ``when the trap is launched by an @command{exit}, what is
13006 the @emph{last} command run: that before @command{exit}, or
13007 @command{exit} itself?''
13009 Bash considers @command{exit} to be the last command, while Zsh and
13010 Solaris @command{/bin/sh} consider that when the trap is run it is
13011 @emph{still} in the @command{exit}, hence it is the previous exit status
13012 that the trap receives:
13015 $ @kbd{cat trap.sh}
13018 $ @kbd{zsh trap.sh}
13020 $ @kbd{bash trap.sh}
13024 The portable solution is then simple: when you want to @samp{exit 42},
13025 run @samp{(exit 42); exit 42}, the first @command{exit} being used to
13026 set the exit status to 42 for Zsh, and the second to trigger the trap
13027 and pass 42 as exit status for Bash.
13029 The shell in Free@acronym{BSD} 4.0 has the following bug: @samp{$?} is
13030 reset to 0 by empty lines if the code is inside @command{trap}.
13033 $ @kbd{trap 'false}
13041 Fortunately, this bug only affects @command{trap}.
13043 @item @command{true}
13044 @c -----------------
13045 @prindex @command{true}
13046 @c Info cannot handle `:' in index entries.
13047 @c @prindex @command{:}
13048 Don't worry: as far as we know @command{true} is portable.
13049 Nevertheless, it's not always a builtin (e.g., Bash 1.x), and the
13050 portable shell community tends to prefer using @command{:}. This has a
13051 funny side effect: when asked whether @command{false} is more portable
13052 than @command{true} Alexandre Oliva answered:
13055 In a sense, yes, because if it doesn't exist, the shell will produce an
13056 exit status of failure, which is correct for @command{false}, but not
13057 for @command{true}.
13061 @item @command{unset}
13062 @c ------------------
13063 @prindex @command{unset}
13064 In some nonconforming shells (e.g., Bash 2.05a), @code{unset FOO} fails
13065 when @code{FOO} is not set. Also, Bash 2.01 mishandles @code{unset
13066 MAIL} in some cases and dumps core.
13068 A few ancient shells lack @command{unset} entirely. Nevertheless, because
13069 it is extremely useful to disable embarrassing variables such as
13070 @code{PS1}, you can test for its existence and use
13071 it @emph{provided} you give a neutralizing value when @command{unset} is
13075 # "|| exit" suppresses any "Segmentation fault" message.
13076 if ( (MAIL=60; unset MAIL) || exit) >/dev/null 2>&1; then
13081 $unset PS1 || PS1='$ '
13085 @xref{Special Shell Variables}, for some neutralizing values. Also, see
13086 @ref{Limitations of Builtins}, documentation of @command{export}, for
13087 the case of environment variables.
13090 @node Limitations of Usual Tools
13091 @section Limitations of Usual Tools
13092 @cindex Limitations of usual tools
13094 The small set of tools you can expect to find on any machine can still
13095 include some limitations you should be aware of.
13101 Don't leave white space before the opening parenthesis in a user function call.
13102 Posix does not allow this and @acronym{GNU} Awk rejects it:
13105 $ @kbd{gawk 'function die () @{ print "Aaaaarg!" @}
13106 BEGIN @{ die () @}'}
13107 gawk: cmd. line:2: BEGIN @{ die () @}
13108 gawk: cmd. line:2: ^ parse error
13109 $ @kbd{gawk 'function die () @{ print "Aaaaarg!" @}
13110 BEGIN @{ die() @}'}
13114 Posix says that if a program contains only @samp{BEGIN} actions, and
13115 contains no instances of @code{getline}, then the program merely
13116 executes the actions without reading input. However, traditional Awk
13117 implementations (such as Solaris 10 @command{awk}) read and discard
13118 input in this case. Portable scripts can redirect input from
13119 @file{/dev/null} to work around the problem. For example:
13122 awk 'BEGIN @{print "hello world"@}' </dev/null
13125 If you want your program to be deterministic, don't depend on @code{for}
13129 $ @kbd{cat for.awk}
13136 $ @kbd{gawk -f for.awk </dev/null}
13139 $ @kbd{nawk -f for.awk </dev/null}
13144 Some Awk implementations, such as @acronym{HP-UX} 11.0's native one, mishandle anchors:
13147 $ @kbd{echo xfoo | $AWK '/foo|^bar/ @{ print @}'}
13148 $ @kbd{echo bar | $AWK '/foo|^bar/ @{ print @}'}
13150 $ @kbd{echo xfoo | $AWK '/^bar|foo/ @{ print @}'}
13152 $ @kbd{echo bar | $AWK '/^bar|foo/ @{ print @}'}
13157 Either do not depend on such patterns (i.e., use @samp{/^(.*foo|bar)/},
13158 or use a simple test to reject such implementations.
13160 @acronym{AIX} version 5.2 has an arbitrary limit of 399 on the
13161 length of regular expressions and literal strings in an Awk program.
13163 Traditional Awk implementations derived from Unix version 7, such as
13164 Solaris @command{/bin/awk}, have many limitations and do not
13165 conform to Posix. Nowadays @code{AC_PROG_AWK} (@pxref{Particular
13166 Programs}) finds you an Awk that doesn't have these problems, but if
13167 for some reason you prefer not to use @code{AC_PROG_AWK} you may need to
13170 Traditional Awk does not support multidimensional arrays or user-defined
13173 Traditional Awk does not support the @option{-v} option. You can use
13174 assignments after the program instead, e.g., @command{$AWK '@{print v
13175 $1@}' v=x}; however, don't forget that such assignments are not
13176 evaluated until they are encountered (e.g., after any @code{BEGIN}
13179 Traditional Awk does not support the keywords @code{delete} or @code{do}.
13181 Traditional Awk does not support the expressions
13182 @code{@var{a}?@var{b}:@var{c}}, @code{!@var{a}}, @code{@var{a}^@var{b}},
13183 or @code{@var{a}^=@var{b}}.
13185 Traditional Awk does not support the predefined @code{CONVFMT} variable.
13187 Traditional Awk supports only the predefined functions @code{exp},
13188 @code{int}, @code{length}, @code{log}, @code{split}, @code{sprintf},
13189 @code{sqrt}, and @code{substr}.
13191 Traditional Awk @code{getline} is not at all compatible with Posix;
13194 Traditional Awk has @code{for (i in a) @dots{}} but no other uses of the
13195 @code{in} keyword. For example, it lacks @code{if (i in a) @dots{}}.
13197 In code portable to both traditional and modern Awk, @code{FS} must be a
13198 string containing just one ordinary character, and similarly for the
13199 field-separator argument to @code{split}.
13201 Traditional Awk has a limit of 99
13202 fields in a record. You may be able to circumvent this problem by using
13205 Traditional Awk has a limit of at most 99 bytes in a number formatted by
13206 @code{OFMT}; for example, @code{OFMT="%.300e"; print 0.1;} typically
13209 The original version of Awk had a limit of at most 99 bytes per
13210 @code{split} field, 99 bytes per @code{substr} substring, and 99 bytes
13211 per run of non-special characters in a @code{printf} format, but these
13212 bugs have been fixed on all practical hosts that we know of.
13214 @item @command{basename}
13215 @c ---------------------
13216 @prindex @command{basename}
13217 Not all hosts have a working @command{basename}.
13218 You can use @command{expr} instead.
13220 @c AS_BASENAME is to be replaced by a better API.
13222 Not all hosts have a working @command{basename}, and you should instead
13223 use @code{AS_BASENAME} (@pxref{Programming in M4sh}), followed by
13224 @command{expr} if you need to strip a suffix. For example:
13227 a=`basename "$aname"` # This is not portable.
13228 a=`AS_BASENAME(["$aname"])` # This is more portable.
13230 # This is not portable.
13231 c=`basename "$cname" .c`
13233 # This is more portable.
13234 c=`AS_BASENAME(["$cname"])`
13236 ?*.c) c=`expr "X$c" : 'X\(.*\)\.c'`;;
13242 @item @command{cat}
13243 @c ----------------
13244 @prindex @command{cat}
13245 Don't rely on any option.
13250 @prindex @command{cc}
13251 The command @samp{cc -c foo.c} traditionally produces an object file
13252 named @file{foo.o}. Most compilers allow @option{-c} to be combined
13253 with @option{-o} to specify a different object file name, but
13254 Posix does not require this combination and a few compilers
13255 lack support for it. @xref{C Compiler}, for how @acronym{GNU} Make
13256 tests for this feature with @code{AC_PROG_CC_C_O}.
13258 When a compilation such as @samp{cc -o foo foo.c} fails, some compilers
13259 (such as @sc{cds} on Reliant Unix) leave a @file{foo.o}.
13261 @acronym{HP-UX} @command{cc} doesn't accept @file{.S} files to preprocess and
13262 assemble. @samp{cc -c foo.S} appears to succeed, but in fact does
13265 The default executable, produced by @samp{cc foo.c}, can be
13268 @item @file{a.out} --- usual Posix convention.
13269 @item @file{b.out} --- i960 compilers (including @command{gcc}).
13270 @item @file{a.exe} --- @acronym{DJGPP} port of @command{gcc}.
13271 @item @file{a_out.exe} --- GNV @command{cc} wrapper for DEC C on OpenVMS.
13272 @item @file{foo.exe} --- various MS-DOS compilers.
13275 The C compiler's traditional name is @command{cc}, but other names like
13276 @command{gcc} are common. Posix 1003.1-2001 specifies the
13277 name @command{c99}, but older Posix editions specified
13278 @command{c89} and anyway these standard names are rarely used in
13279 practice. Typically the C compiler is invoked from makefiles that use
13280 @samp{$(CC)}, so the value of the @samp{CC} make variable selects the
13284 @item @command{chmod}
13285 @c ------------------
13286 @prindex @command{chmod}
13287 Avoid usages like @samp{chmod -w file}; use @samp{chmod a-w file}
13288 instead, for two reasons. First, plain @option{-w} does not necessarily
13289 make the file unwritable, since it does not affect mode bits that
13290 correspond to bits in the file mode creation mask. Second,
13291 Posix says that the @option{-w} might be interpreted as an
13292 implementation-specific option, not as a mode; Posix suggests
13293 using @samp{chmod -- -w file} to avoid this confusion, but unfortunately
13294 @samp{--} does not work on some older hosts.
13297 @item @command{cmp}
13298 @c ----------------
13299 @prindex @command{cmp}
13300 @command{cmp} performs a raw data comparison of two files, while
13301 @command{diff} compares two text files. Therefore, if you might compare
13302 DOS files, even if only checking whether two files are different, use
13303 @command{diff} to avoid spurious differences due to differences of
13309 @prindex @command{cp}
13310 Avoid the @option{-r} option, since Posix 1003.1-2004 marks it as
13311 obsolescent and its behavior on special files is implementation-defined.
13312 Use @option{-R} instead. On @acronym{GNU} hosts the two options
13313 are equivalent, but on Solaris hosts (for example) @command{cp -r}
13314 reads from pipes instead of replicating them.
13316 Some @command{cp} implementations (e.g., @acronym{BSD/OS} 4.2) do not allow
13317 trailing slashes at the end of nonexistent destination directories. To
13318 avoid this problem, omit the trailing slashes. For example, use
13319 @samp{cp -R source /tmp/newdir} rather than @samp{cp -R source
13320 /tmp/newdir/} if @file{/tmp/newdir} does not exist.
13322 @c This is thanks to Ian.
13323 The ancient SunOS 4 @command{cp} does not support @option{-f}, although
13324 its @command{mv} does.
13326 @cindex timestamp resolution
13327 Traditionally, file timestamps had 1-second resolution, and @samp{cp
13328 -p} copied the timestamps exactly. However, many modern file systems
13329 have timestamps with 1-nanosecond resolution. Unfortunately, @samp{cp
13330 -p} implementations truncate timestamps when copying files, so this
13331 can result in the destination file appearing to be older than the
13332 source. The exact amount of truncation depends on the resolution of
13333 the system calls that @command{cp} uses; traditionally this was
13334 @code{utime}, which has 1-second resolution, but some newer
13335 @command{cp} implementations use @code{utimes}, which has
13336 1-microsecond resolution. These newer implementations include @acronym{GNU}
13337 Core Utilities 5.0.91 or later, and Solaris 8 (sparc) patch 109933-02 or
13338 later. Unfortunately as of January 2006 there is still no system
13339 call to set timestamps to the full nanosecond resolution.
13341 Bob Proulx notes that @samp{cp -p} always @emph{tries} to copy
13342 ownerships. But whether it actually does copy ownerships or not is a
13343 system dependent policy decision implemented by the kernel. If the
13344 kernel allows it then it happens. If the kernel does not allow it then
13345 it does not happen. It is not something @command{cp} itself has control
13348 In Unix System V any user can chown files to any other user, and System
13349 V also has a non-sticky @file{/tmp}. That probably derives from the
13350 heritage of System V in a business environment without hostile users.
13351 @acronym{BSD} changed this
13352 to be a more secure model where only root can @command{chown} files and
13353 a sticky @file{/tmp} is used. That undoubtedly derives from the heritage
13354 of @acronym{BSD} in a campus environment.
13356 @acronym{GNU}/Linux and Solaris by default follow @acronym{BSD}, but
13357 can be configured to allow a System V style @command{chown}. On the
13358 other hand, @acronym{HP-UX} follows System V, but can
13359 be configured to use the modern security model and disallow
13360 @command{chown}. Since it is an administrator-configurable parameter
13361 you can't use the name of the kernel as an indicator of the behavior.
13365 @item @command{date}
13366 @c -----------------
13367 @prindex @command{date}
13368 Some versions of @command{date} do not recognize special @samp{%} directives,
13369 and unfortunately, instead of complaining, they just pass them through,
13370 and exit with success:
13374 OSF1 medusa.sis.pasteur.fr V5.1 732 alpha
13380 @item @command{diff}
13381 @c -----------------
13382 @prindex @command{diff}
13383 Option @option{-u} is nonportable.
13385 Some implementations, such as Tru64's, fail when comparing to
13386 @file{/dev/null}. Use an empty file instead.
13389 @item @command{dirname}
13390 @c --------------------
13391 @prindex @command{dirname}
13392 Not all hosts have a working @command{dirname}, and you should instead
13393 use @code{AS_DIRNAME} (@pxref{Programming in M4sh}). For example:
13396 dir=`dirname "$file"` # This is not portable.
13397 dir=`AS_DIRNAME(["$file"])` # This is more portable.
13401 @item @command{egrep}
13402 @c ------------------
13403 @prindex @command{egrep}
13404 Posix 1003.1-2001 no longer requires @command{egrep},
13405 but many hosts do not yet support the Posix
13406 replacement @code{grep -E}. Also, some traditional implementations do
13407 not work on long input lines. To work around these problems, invoke
13408 @code{AC_PROG_EGREP} and then use @code{$EGREP}.
13410 Portable extended regular expressions should use @samp{\} only to escape
13411 characters in the string @samp{$()*+.?[\^@{|}. For example, @samp{\@}}
13412 is not portable, even though it typically matches @samp{@}}.
13414 The empty alternative is not portable. Use @samp{?} instead. For
13415 instance with Digital Unix v5.0:
13418 > printf "foo\n|foo\n" | $EGREP '^(|foo|bar)$'
13420 > printf "bar\nbar|\n" | $EGREP '^(foo|bar|)$'
13422 > printf "foo\nfoo|\n|bar\nbar\n" | $EGREP '^(foo||bar)$'
13427 @command{$EGREP} also suffers the limitations of @command{grep}.
13429 @item @command{expr}
13430 @c -----------------
13431 @prindex @command{expr}
13432 No @command{expr} keyword starts with @samp{X}, so use @samp{expr
13433 X"@var{word}" : 'X@var{regex}'} to keep @command{expr} from
13434 misinterpreting @var{word}.
13436 Don't use @code{length}, @code{substr}, @code{match} and @code{index}.
13438 @item @command{expr} (@samp{|})
13439 @prindex @command{expr} (@samp{|})
13440 You can use @samp{|}. Although Posix does require that @samp{expr
13441 ''} return the empty string, it does not specify the result when you
13442 @samp{|} together the empty string (or zero) with the empty string. For
13449 Posix 1003.2-1992 returns the empty string
13450 for this case, but traditional Unix returns @samp{0} (Solaris is
13451 one such example). In Posix 1003.1-2001, the specification was
13452 changed to match traditional Unix's behavior (which is
13453 bizarre, but it's too late to fix this). Please note that the same
13454 problem does arise when the empty string results from a computation,
13458 expr bar : foo \| foo : bar
13462 Avoid this portability problem by avoiding the empty string.
13465 @item @command{expr} (@samp{:})
13466 @c ----------------------------
13467 @prindex @command{expr}
13468 Portable @command{expr} regular expressions should use @samp{\} to
13469 escape only characters in the string @samp{$()*.0123456789[\^n@{@}}.
13470 For example, alternation, @samp{\|}, is common but Posix does not
13471 require its support, so it should be avoided in portable scripts.
13472 Similarly, @samp{\+} and @samp{\?} should be avoided.
13474 Portable @command{expr} regular expressions should not begin with
13475 @samp{^}. Patterns are automatically anchored so leading @samp{^} is
13478 The Posix standard is ambiguous as to whether
13479 @samp{expr 'a' : '\(b\)'} outputs @samp{0} or the empty string.
13480 In practice, it outputs the empty string on most platforms, but portable
13481 scripts should not assume this. For instance, the @acronym{QNX} 4.25 native
13482 @command{expr} returns @samp{0}.
13484 One might think that a way to get a uniform behavior would be to use
13485 the empty string as a default value:
13488 expr a : '\(b\)' \| ''
13492 Unfortunately this behaves exactly as the original expression; see the
13493 @command{expr} (@samp{|}) entry for more information.
13495 Ancient @command{expr} implementations (e.g., SunOS 4 @command{expr} and
13496 Solaris 8 @command{/usr/ucb/expr}) have a silly length limit that causes
13497 @command{expr} to fail if the matched substring is longer than 120
13498 bytes. In this case, you might want to fall back on @samp{echo|sed} if
13499 @command{expr} fails. Nowadays this is of practical importance only for
13500 the rare installer who mistakenly puts @file{/usr/ucb} before
13501 @file{/usr/bin} in @env{PATH}.
13503 On Mac OS X 10.4, @command{expr} mishandles the pattern @samp{[^-]} in
13504 some cases. For example, the command
13506 expr Xpowerpc-apple-darwin8.1.0 : 'X[^-]*-[^-]*-\(.*\)'
13510 outputs @samp{apple-darwin8.1.0} rather than the correct @samp{darwin8.1.0}.
13511 This particular case can be worked around by substituting @samp{[^--]}
13514 Don't leave, there is some more!
13516 The @acronym{QNX} 4.25 @command{expr}, in addition of preferring @samp{0} to
13517 the empty string, has a funny behavior in its exit status: it's always 1
13518 when parentheses are used!
13521 $ @kbd{val=`expr 'a' : 'a'`; echo "$?: $val"}
13523 $ @kbd{val=`expr 'a' : 'b'`; echo "$?: $val"}
13526 $ @kbd{val=`expr 'a' : '\(a\)'`; echo "?: $val"}
13528 $ @kbd{val=`expr 'a' : '\(b\)'`; echo "?: $val"}
13533 In practice this can be a big problem if you are ready to catch failures
13534 of @command{expr} programs with some other method (such as using
13535 @command{sed}), since you may get twice the result. For instance
13538 $ @kbd{expr 'a' : '\(a\)' || echo 'a' | sed 's/^\(a\)$/\1/'}
13542 outputs @samp{a} on most hosts, but @samp{aa} on @acronym{QNX} 4.25. A
13543 simple workaround consists of testing @command{expr} and using a variable
13544 set to @command{expr} or to @command{false} according to the result.
13546 Tru64 @command{expr} incorrectly treats the result as a number, if it
13547 can be interpreted that way:
13550 $ @kbd{expr 00001 : '.*\(...\)'}
13555 @item @command{fgrep}
13556 @c ------------------
13557 @prindex @command{fgrep}
13558 Posix 1003.1-2001 no longer requires @command{fgrep},
13559 but many hosts do not yet support the Posix
13560 replacement @code{grep -F}. Also, some traditional implementations do
13561 not work on long input lines. To work around these problems, invoke
13562 @code{AC_PROG_FGREP} and then use @code{$FGREP}.
13565 @item @command{find}
13566 @c -----------------
13567 @prindex @command{find}
13568 The option @option{-maxdepth} seems to be @acronym{GNU} specific.
13569 Tru64 v5.1, Net@acronym{BSD} 1.5 and Solaris @command{find}
13570 commands do not understand it.
13572 The replacement of @samp{@{@}} is guaranteed only if the argument is
13573 exactly @emph{@{@}}, not if it's only a part of an argument. For
13574 instance on DU, and @acronym{HP-UX} 10.20 and @acronym{HP-UX} 11:
13578 $ @kbd{find . -name foo -exec echo "@{@}-@{@}" \;}
13583 while @acronym{GNU} @command{find} reports @samp{./foo-./foo}.
13586 @item @command{grep}
13587 @c -----------------
13588 @prindex @command{grep}
13589 Portable scripts can rely on the @command{grep} options @option{-c},
13590 @option{-l}, @option{-n}, and @option{-v}, but should avoid other
13591 options. For example, don't use @option{-w}, as Posix does not require
13592 it and Irix 6.5.16m's @command{grep} does not support it. Also,
13593 portable scripts should not combine @option{-c} with @option{-l},
13594 as Posix does not allow this.
13596 Some of the options required by Posix are not portable in practice.
13597 Don't use @samp{grep -q} to suppress output, because many @command{grep}
13598 implementations (e.g., Solaris) do not support @option{-q}.
13599 Don't use @samp{grep -s} to suppress output either, because Posix
13600 says @option{-s} does not suppress output, only some error messages;
13601 also, the @option{-s} option of traditional @command{grep} behaved
13602 like @option{-q} does in most modern implementations. Instead,
13603 redirect the standard output and standard error (in case the file
13604 doesn't exist) of @code{grep} to @file{/dev/null}. Check the exit
13605 status of @code{grep} to determine whether it found a match.
13607 Some traditional @command{grep} implementations do not work on long
13608 input lines. On AIX the default @code{grep} silently truncates long
13609 lines on the input before matching.
13611 Also, many implementations do not support multiple regexps
13612 with @option{-e}: they either reject @option{-e} entirely (e.g., Solaris)
13613 or honor only the last pattern (e.g., @acronym{IRIX} 6.5 and NeXT). To
13614 work around these problems, invoke @code{AC_PROG_GREP} and then use
13617 Another possible workaround for the multiple @option{-e} problem is to
13618 separate the patterns by newlines, for example:
13626 except that this fails with traditional @command{grep}
13627 implementations and with Open@acronym{BSD} 3.8 @command{grep}.
13629 Traditional @command{grep} implementations (e.g., Solaris) do not
13630 support the @option{-E} or @option{-F} options. To work around these
13631 problems, invoke @code{AC_PROG_EGREP} and then use @code{$EGREP}, and
13632 similarly for @code{AC_PROG_FGREP} and @code{$FGREP}. Even if you are
13633 willing to require support for Posix @command{grep}, your script should
13634 not use both @option{-E} and @option{-F}, since Posix does not allow
13637 Portable @command{grep} regular expressions should use @samp{\} only to
13638 escape characters in the string @samp{$()*.0123456789[\^@{@}}. For example,
13639 alternation, @samp{\|}, is common but Posix does not require its
13640 support in basic regular expressions, so it should be avoided in
13641 portable scripts. Solaris and HP-UX @command{grep} do not support it.
13642 Similarly, the following escape sequences should also be avoided:
13643 @samp{\<}, @samp{\>}, @samp{\+}, @samp{\?}, @samp{\`}, @samp{\'},
13644 @samp{\B}, @samp{\b}, @samp{\S}, @samp{\s}, @samp{\W}, and @samp{\w}.
13647 @item @command{join}
13648 @c -----------------
13649 @prindex @command{join}
13650 Solaris 8 @command{join} has bugs when the second operand is standard
13651 input, and when standard input is a pipe. For example, the following
13652 shell script causes Solaris 8 @command{join} to loop forever:
13659 cat file | join file -
13662 Use @samp{join - file} instead.
13667 @prindex @command{ln}
13668 @cindex Symbolic links
13669 Don't rely on @command{ln} having a @option{-f} option. Symbolic links
13670 are not available on old systems; use @samp{$(LN_S)} as a portable substitute.
13672 For versions of the @acronym{DJGPP} before 2.04,
13673 @command{ln} emulates symbolic links
13674 to executables by generating a stub that in turn calls the real
13675 program. This feature also works with nonexistent files like in the
13676 Posix spec. So @samp{ln -s file link} generates @file{link.exe},
13677 which attempts to call @file{file.exe} if run. But this feature only
13678 works for executables, so @samp{cp -p} is used instead for these
13679 systems. @acronym{DJGPP} versions 2.04 and later have full support
13680 for symbolic links.
13685 @prindex @command{ls}
13686 @cindex Listing directories
13687 The portable options are @option{-acdilrtu}. Current practice is for
13688 @option{-l} to output both owner and group, even though ancient versions
13689 of @command{ls} omitted the group.
13691 On ancient hosts, @samp{ls foo} sent the diagnostic @samp{foo not found}
13692 to standard output if @file{foo} did not exist. Hence a shell command
13693 like @samp{sources=`ls *.c 2>/dev/null`} did not always work, since it
13694 was equivalent to @samp{sources='*.c not found'} in the absence of
13695 @samp{.c} files. This is no longer a practical problem, since current
13696 @command{ls} implementations send diagnostics to standard error.
13698 @item @command{mkdir}
13699 @c ------------------
13700 @prindex @command{mkdir}
13701 @cindex Making directories
13702 No @command{mkdir} option is portable to older systems. Instead of
13703 @samp{mkdir -p @var{file-name}}, you should use
13704 @code{AS_MKDIR_P(@var{file-name})} (@pxref{Programming in M4sh})
13705 or @code{AC_PROG_MKDIR_P} (@pxref{Particular Programs}).
13707 Combining the @option{-m} and @option{-p} options, as in @samp{mkdir -m
13708 go-w -p @var{dir}}, often leads to trouble. Free@acronym{BSD}
13709 @command{mkdir} incorrectly attempts to change the permissions of
13710 @var{dir} even if it already exists. @acronym{HP-UX} 11.23 and
13711 @acronym{IRIX} 6.5 @command{mkdir} often assign the wrong permissions to
13712 any newly-created parents of @var{dir}.
13714 Posix does not clearly specify whether @samp{mkdir -p foo}
13715 should succeed when @file{foo} is a symbolic link to an already-existing
13716 directory. The @acronym{GNU} Core Utilities 5.1.0 @command{mkdir}
13717 succeeds, but Solaris @command{mkdir} fails.
13719 Traditional @code{mkdir -p} implementations suffer from race conditions.
13720 For example, if you invoke @code{mkdir -p a/b} and @code{mkdir -p a/c}
13721 at the same time, both processes might detect that @file{a} is missing,
13722 one might create @file{a}, then the other might try to create @file{a}
13723 and fail with a @code{File exists} diagnostic. The @acronym{GNU} Core
13724 Utilities (@samp{fileutils} version 4.1), Free@acronym{BSD} 5.0,
13725 Net@acronym{BSD} 2.0.2, and Open@acronym{BSD} 2.4 are known to be
13726 race-free when two processes invoke @code{mkdir -p} simultaneously, but
13727 earlier versions are vulnerable. Solaris @command{mkdir} is still
13728 vulnerable as of Solaris 10, and other traditional Unix systems are
13729 probably vulnerable too. This possible race is harmful in parallel
13730 builds when several Make rules call @code{mkdir -p} to
13731 construct directories. You may use
13732 @code{install-sh -d} as a safe replacement, provided this script is
13733 recent enough; the copy shipped with Autoconf 2.60 and Automake 1.10 is
13734 OK, but copies from older versions are vulnerable.
13737 @item @command{mktemp}
13738 @c -------------------
13739 @prindex @command{mktemp}
13740 @cindex Creating temporary files
13741 Shell scripts can use temporary files safely with @command{mktemp}, but
13742 it does not exist on all systems. A portable way to create a safe
13743 temporary file name is to create a temporary directory with mode 700 and
13744 use a file inside this directory. Both methods prevent attackers from
13745 gaining control, though @command{mktemp} is far less likely to fail
13746 gratuitously under attack.
13748 Here is sample code to create a new temporary directory safely:
13751 # Create a temporary directory $tmp in $TMPDIR (default /tmp).
13752 # Use mktemp if possible; otherwise fall back on mkdir,
13753 # with $RANDOM to make collisions less likely.
13757 (umask 077 && mktemp -d "$TMPDIR/fooXXXXXX") 2>/dev/null
13759 test -n "$tmp" && test -d "$tmp"
13761 tmp=$TMPDIR/foo$$-$RANDOM
13762 (umask 077 && mkdir "$tmp")
13769 @prindex @command{mv}
13770 @cindex Moving open files
13771 The only portable options are @option{-f} and @option{-i}.
13773 Moving individual files between file systems is portable (it was in Unix
13775 but it is not always atomic: when doing @samp{mv new existing}, there's
13776 a critical section where neither the old nor the new version of
13777 @file{existing} actually exists.
13779 On some systems moving files from @file{/tmp} can sometimes cause
13780 undesirable (but perfectly valid) warnings, even if you created these
13781 files. This is because @file{/tmp} belongs to a group that ordinary
13782 users are not members of, and files created in @file{/tmp} inherit
13783 the group of @file{/tmp}. When the file is copied, @command{mv} issues
13784 a diagnostic without failing:
13787 $ @kbd{touch /tmp/foo}
13788 $ @kbd{mv /tmp/foo .}
13789 @error{}mv: ./foo: set owner/group (was: 100/0): Operation not permitted
13797 This annoying behavior conforms to Posix, unfortunately.
13799 Moving directories across mount points is not portable, use @command{cp}
13802 @acronym{DOS} variants cannot rename or remove open files, and do not
13803 support commands like @samp{mv foo bar >foo}, even though this is
13804 perfectly portable among Posix hosts.
13809 @prindex @command{od}
13811 In Mac OS X 10.3, @command{od} does not support the
13812 standard Posix options @option{-A}, @option{-j}, @option{-N}, or
13813 @option{-t}, or the @acronym{XSI} option @option{-s}. The only
13814 supported Posix option is @option{-v}, and the only supported
13815 @acronym{XSI} options are those in @option{-bcdox}. The @acronym{BSD}
13816 @command{hexdump} program can be used instead.
13818 This problem no longer exists in Mac OS X 10.4.3.
13823 @prindex @command{rm}
13824 The @option{-f} and @option{-r} options are portable.
13826 It is not portable to invoke @command{rm} without operands. For
13827 example, on many systems @samp{rm -f -r} (with no other arguments)
13828 silently succeeds without doing anything, but it fails with a diagnostic
13829 on Net@acronym{BSD} 2.0.2.
13831 A file might not be removed even if its parent directory is writable
13832 and searchable. Many Posix hosts cannot remove a mount point, a named
13833 stream, a working directory, or a last link to a file that is being
13836 @acronym{DOS} variants cannot rename or remove open files, and do not
13837 support commands like @samp{rm foo >foo}, even though this is
13838 perfectly portable among Posix hosts.
13841 @item @command{sed}
13842 @c ----------------
13843 @prindex @command{sed}
13844 Patterns should not include the separator (unless escaped), even as part
13845 of a character class. In conformance with Posix, the Cray
13846 @command{sed} rejects @samp{s/[^/]*$//}: use @samp{s,[^/]*$,,}.
13848 Avoid empty patterns within parentheses (i.e., @samp{\(\)}). Posix does
13849 not require support for empty patterns, and Unicos 9 @command{sed} rejects
13852 Unicos 9 @command{sed} loops endlessly on patterns like @samp{.*\n.*}.
13854 Sed scripts should not use branch labels longer than 7 characters and
13855 should not contain comments. @acronym{HP-UX} sed has a limit of 99 commands
13856 (not counting @samp{:} commands) and
13857 48 labels, which can not be circumvented by using more than one script
13858 file. It can execute up to 19 reads with the @samp{r} command per cycle.
13859 Solaris @command{/usr/ucb/sed} rejects usages that exceed an limit of
13860 about 6000 bytes for the internal representation of commands.
13862 Avoid redundant @samp{;}, as some @command{sed} implementations, such as
13863 Net@acronym{BSD} 1.4.2's, incorrectly try to interpret the second
13864 @samp{;} as a command:
13867 $ @kbd{echo a | sed 's/x/x/;;s/x/x/'}
13868 sed: 1: "s/x/x/;;s/x/x/": invalid command code ;
13871 Input should not have unreasonably long lines, since some @command{sed}
13872 implementations have an input buffer limited to 4000 bytes.
13874 Portable @command{sed} regular expressions should use @samp{\} only to escape
13875 characters in the string @samp{$()*.0123456789[\^n@{@}}. For example,
13876 alternation, @samp{\|}, is common but Posix does not require its
13877 support, so it should be avoided in portable scripts. Solaris
13878 @command{sed} does not support alternation; e.g., @samp{sed '/a\|b/d'}
13879 deletes only lines that contain the literal string @samp{a|b}.
13880 Similarly, @samp{\+} and @samp{\?} should be avoided.
13882 Anchors (@samp{^} and @samp{$}) inside groups are not portable.
13884 Nested parentheses in patterns (e.g., @samp{\(\(a*\)b*)\)}) are
13885 quite portable to current hosts, but was not supported by some ancient
13886 @command{sed} implementations like SVR3.
13888 Some @command{sed} implementations, e.g., Solaris,
13889 restrict the special role of the asterisk to one-character regular expressions.
13890 This may lead to unexpected behavior:
13893 $ @kbd{echo '1*23*4' | /usr/bin/sed 's/\(.\)*/x/g'}
13895 $ @kbd{echo '1*23*4' | /usr/xpg4/bin/sed 's/\(.\)*/x/g'}
13899 The @option{-e} option is portable, so long as its argument
13900 does not begin with @samp{a}, @samp{c}, or @samp{i}
13901 (as this runs afoul of a Tru64 5.1 bug).
13902 Some people prefer to use @samp{-e}:
13905 sed -e '@var{command-1}' \
13906 -e '@var{command-2}'
13910 as opposed to the equivalent:
13920 The following usage is sometimes equivalent:
13923 sed '@var{command-1};@var{command-2}'
13926 but Posix says that this use of a semicolon has undefined effect if
13927 @var{command-1}'s verb is @samp{@{}, @samp{a}, @samp{b}, @samp{c},
13928 @samp{i}, @samp{r}, @samp{t}, @samp{w}, @samp{:}, or @samp{#}, so you
13929 should use semicolon only with simple scripts that do not use these
13932 Commands inside @{ @} brackets are further restricted. Posix says that
13933 they cannot be preceded by addresses, @samp{!}, or @samp{;}, and that
13934 each command must be followed immediately by a newline, without any
13935 intervening blanks or semicolons. The closing bracket must be alone on
13936 a line, other than white space preceding or following it.
13938 Contrary to yet another urban legend, you may portably use @samp{&} in
13939 the replacement part of the @code{s} command to mean ``what was
13940 matched''. All descendants of Unix version 7 @command{sed}
13942 don't have first hand experience with older @command{sed} implementations) have
13945 Posix requires that you must not have any white space between
13946 @samp{!} and the following command. It is OK to have blanks between
13947 the address and the @samp{!}. For instance, on Solaris:
13950 $ @kbd{echo "foo" | sed -n '/bar/ ! p'}
13951 @error{}Unrecognized command: /bar/ ! p
13952 $ @kbd{echo "foo" | sed -n '/bar/! p'}
13953 @error{}Unrecognized command: /bar/! p
13954 $ @kbd{echo "foo" | sed -n '/bar/ !p'}
13958 Posix also says that you should not combine @samp{!} and @samp{;}. If
13959 you use @samp{!}, it is best to put it on a command that is delimited by
13960 newlines rather than @samp{;}.
13962 Also note that Posix requires that the @samp{b}, @samp{t}, @samp{r}, and
13963 @samp{w} commands be followed by exactly one space before their argument.
13964 On the other hand, no white space is allowed between @samp{:} and the
13965 subsequent label name.
13967 If a sed script is specified on the command line and ends in an
13968 @samp{a}, @samp{c}, or @samp{i} command, the last line of inserted text
13969 should be followed by a newline. Otherwise some @command{sed}
13970 implementations (e.g., Open@acronym{BSD} 3.9) do not append a newline to the
13973 Many @command{sed} implementations (e.g., MacOS X 10.4,
13974 Open@acronym{BSD} 3.9, Solaris 10
13975 @command{/usr/ucb/sed}) strip leading white space from the text of
13976 @samp{a}, @samp{c}, and @samp{i} commands. Prepend a backslash to
13977 work around this incompatibility with Posix:
13980 $ @kbd{echo flushleft | sed 'a\}
13985 $ @kbd{echo foo | sed 'a\}
13993 @item @command{sed} (@samp{t})
13994 @c ---------------------------
13995 @prindex @command{sed} (@samp{t})
13996 Some old systems have @command{sed} that ``forget'' to reset their
13997 @samp{t} flag when starting a new cycle. For instance on @acronym{MIPS
13998 RISC/OS}, and on @sc{irix} 5.3, if you run the following @command{sed}
13999 script (the line numbers are not actual part of the texts):
14002 s/keep me/kept/g # a
14038 Why? When processing line 1, (c) matches, therefore sets the @samp{t}
14039 flag, and the output is produced. When processing
14040 line 2, the @samp{t} flag is still set (this is the bug). Command (a)
14041 fails to match, but @command{sed} is not supposed to clear the @samp{t}
14042 flag when a substitution fails. Command (b) sees that the flag is set,
14043 therefore it clears it, and jumps to (d), hence you get @samp{delete me}
14044 instead of @samp{deleted}. When processing line (3), @samp{t} is clear,
14045 (a) matches, so the flag is set, hence (b) clears the flags and jumps.
14046 Finally, since the flag is clear, line 4 is processed properly.
14048 There are two things one should remember about @samp{t} in @command{sed}.
14049 Firstly, always remember that @samp{t} jumps if @emph{some} substitution
14050 succeeded, not only the immediately preceding substitution. Therefore,
14051 always use a fake @samp{t clear} followed by a @samp{:clear} on the next
14052 line, to reset the @samp{t} flag where needed.
14054 Secondly, you cannot rely on @command{sed} to clear the flag at each new
14057 One portable implementation of the script above is:
14068 @item @command{touch}
14069 @c ------------------
14070 @prindex @command{touch}
14071 @cindex timestamp resolution
14072 If you specify the desired timestamp (e.g., with the @option{-r}
14073 option), @command{touch} typically uses the @code{utime} or
14074 @code{utimes} system call, which can result in the same kind of
14075 timestamp truncation problems that @samp{cp -p} has.
14077 On ancient @acronym{BSD} systems, @command{touch} or any command that
14078 results in an empty file does not update the timestamps, so use a
14079 command like @command{echo} as a workaround.
14081 @acronym{GNU} @command{touch} 3.16r (and presumably all before that)
14082 fails to work on SunOS 4.1.3 when the empty file is on an
14083 @acronym{NFS}-mounted 4.2 volume.
14084 However, these problems are no longer of practical concern.
14089 @node Portable Make
14090 @chapter Portable Make Programming
14091 @prindex @command{make}
14092 @cindex Limitations of @command{make}
14094 Writing portable makefiles is an art. Since a makefile's commands are
14095 executed by the shell, you must consider the shell portability issues
14096 already mentioned. However, other issues are specific to @command{make}
14100 * $< in Ordinary Make Rules:: $< in ordinary rules
14101 * Failure in Make Rules:: Failing portably in rules
14102 * Special Chars in Names:: Special Characters in Macro Names
14103 * Backslash-Newline-Newline:: Empty last lines in macro definitions
14104 * Backslash-Newline Comments:: Spanning comments across line boundaries
14105 * Long Lines in Makefiles:: Line length limitations
14106 * Macros and Submakes:: @code{make macro=value} and submakes
14107 * The Make Macro MAKEFLAGS:: @code{$(MAKEFLAGS)} portability issues
14108 * The Make Macro SHELL:: @code{$(SHELL)} portability issues
14109 * Comments in Make Rules:: Other problems with Make comments
14110 * obj/ and Make:: Don't name a subdirectory @file{obj}
14111 * make -k Status:: Exit status of @samp{make -k}
14112 * VPATH and Make:: @code{VPATH} woes
14113 * Single Suffix Rules:: Single suffix rules and separated dependencies
14114 * Timestamps and Make:: Subsecond timestamp resolution
14117 @node $< in Ordinary Make Rules
14118 @section @code{$<} in Ordinary Make Rules
14120 Posix says that the @samp{$<} construct in makefiles can be
14121 used only in inference rules and in the @samp{.DEFAULT} rule; its
14122 meaning in ordinary rules is unspecified. Solaris @command{make}
14123 for instance replaces it with the empty string. Open@acronym{BSD} (3.0 and
14124 later) @command{make} diagnoses these uses and errors out.
14126 @node Failure in Make Rules
14127 @section Failure in Make Rules
14129 Since 1992 Posix has required that @command{make} must invoke
14130 each command with the equivalent of a @samp{sh -c} subshell. However,
14131 many @command{make} implementations, including @acronym{BSD} make through 2004,
14132 use @samp{sh -e -c} instead, and the @option{-e} option causes the
14133 subshell to exit immediately if a subsidiary simple-command fails. For
14134 example, the command @samp{touch T; rm -f U} always attempts to
14135 remove @file{U} with Posix make, but incompatible
14136 @command{make} implementations skip the @command{rm} if the
14137 @command{touch} fails. One way to work around this is to reword the
14138 affected simple-commands so that they always succeed, e.g., @samp{touch
14140 However, even this approach can run into common bugs in @acronym{BSD}
14141 implementations of the @option{-e} option of @command{sh} and
14142 @command{set} (@pxref{Limitations of Builtins}), so if you are worried
14143 about porting to buggy @acronym{BSD} shells it may be simpler to migrate
14144 complicated @command{make} actions into separate scripts.
14146 @node Special Chars in Names
14147 @section Special Characters in Make Macro Names
14149 Posix limits macro names to nonempty strings containing only
14150 @acronym{ASCII} letters and digits, @samp{.}, and @samp{_}. Many
14151 @command{make} implementations allow a wider variety of characters, but
14152 portable makefiles should avoid them. It is portable to start a name
14153 with a special character, e.g., @samp{$(.FOO)}.
14155 Some ancient @command{make} implementations don't support leading
14156 underscores in macro names. An example is @acronym{NEWS-OS} 4.2R.
14159 $ @kbd{cat Makefile}
14162 all:; @@echo this is test
14164 Make: Must be a separator on rules line 2. Stop.
14165 $ @kbd{cat Makefile2}
14168 all:; @@echo this is test
14169 $ @kbd{make -f Makefile2}
14174 However, this problem is no longer of practical concern.
14176 @node Backslash-Newline-Newline
14177 @section Backslash-Newline-Newline in Make Macro Values
14179 @c This has been seen on ia64 hpux 11.20, and on one hppa hpux 10.20,
14180 @c but another hppa hpux 10.20 didn't have it. Bob Proulx
14181 @c <bob@proulx.com> thinks it was in hpux 8.0 too.
14182 On some versions of @acronym{HP-UX}, @command{make} reads multiple newlines
14183 following a backslash, continuing to the next non-empty line. For
14197 shows @code{FOO} equal to @code{one BAR = two}. Other implementations
14198 sensibly let a backslash continue only to the immediately following
14201 @node Backslash-Newline Comments
14202 @section Backslash-Newline in Make Comments
14204 According to Posix, Make comments start with @code{#}
14205 and continue until an unescaped newline is reached.
14208 $ @kbd{cat Makefile}
14215 $ @kbd{make} # GNU make
14220 However this is not always the case. Some implementations
14221 discard everything from @code{#} through the end of the line, ignoring any
14222 trailing backslash.
14225 $ @kbd{pmake} # BSD make
14226 "Makefile", line 3: Need an operator
14227 Fatal errors encountered -- cannot continue
14231 Therefore, if you want to comment out a multi-line definition, prefix each
14232 line with @code{#}, not only the first.
14240 @node Long Lines in Makefiles
14241 @section Long Lines in Makefiles
14243 Tru64 5.1's @command{make} has been reported to crash when given a
14244 makefile with lines longer than around 20 kB. Earlier versions are
14245 reported to exit with @code{Line too long} diagnostics.
14247 @node Macros and Submakes
14248 @section @code{make macro=value} and Submakes
14250 A command-line variable definition such as @code{foo=bar} overrides any
14251 definition of @code{foo} in a makefile. Some @command{make}
14252 implementations (such as @acronym{GNU} @command{make}) propagate this
14253 override to subsidiary invocations of @command{make}. Some other
14254 implementations do not pass the substitution along to submakes.
14257 $ @kbd{cat Makefile}
14264 $ @kbd{make foo=bar} # GNU make 3.79.1
14267 make[1]: Entering directory `/home/adl'
14269 make[1]: Leaving directory `/home/adl'
14270 $ @kbd{pmake foo=bar} # BSD make
14276 You have a few possibilities if you do want the @code{foo=bar} override
14277 to propagate to submakes. One is to use the @option{-e}
14278 option, which causes all environment variables to have precedence over
14279 the makefile macro definitions, and declare foo as an environment
14283 $ @kbd{env foo=bar make -e}
14286 The @option{-e} option is propagated to submakes automatically,
14287 and since the environment is inherited between @command{make}
14288 invocations, the @code{foo} macro is overridden in
14289 submakes as expected.
14291 This syntax (@code{foo=bar make -e}) is portable only when used
14292 outside of a makefile, for instance from a script or from the
14293 command line. When run inside a @command{make} rule, @acronym{GNU}
14294 @command{make} 3.80 and prior versions forget to propagate the
14295 @option{-e} option to submakes.
14297 Moreover, using @option{-e} could have unexpected side effects if your
14298 environment contains some other macros usually defined by the
14299 makefile. (See also the note about @code{make -e} and @code{SHELL}
14302 Another way to propagate overrides to submakes is to do it
14303 manually, from your makefile:
14309 $(MAKE) foo=$(foo) two
14314 You need to foresee all macros that a user might want to override if
14317 @node The Make Macro MAKEFLAGS
14318 @section The Make Macro MAKEFLAGS
14319 @cindex @code{MAKEFLAGS} and @command{make}
14320 @cindex @command{make} and @code{MAKEFLAGS}
14322 Posix requires @command{make} to use @code{MAKEFLAGS} to affect the
14323 current and recursive invocations of make, but allows implementations
14324 several formats for the variable. It is tricky to parse
14325 @code{$MAKEFLAGS} to determine whether @option{-s} for silent execution
14326 or @option{-k} for continued execution are in effect. For example, you
14327 cannot assume that the first space-separated word in @code{$MAKEFLAGS}
14328 contains single-letter options, since in the Cygwin version of
14329 @acronym{GNU} @command{make} it is either @option{--unix} or
14330 @option{--win32} with the second word containing single-letter options.
14333 $ @kbd{cat Makefile}
14335 @@echo MAKEFLAGS = $(MAKEFLAGS)
14339 MAKEFLAGS = --unix -k
14342 @node The Make Macro SHELL
14343 @section The Make Macro @code{SHELL}
14344 @cindex @code{SHELL} and @command{make}
14345 @cindex @command{make} and @code{SHELL}
14347 Posix-compliant @command{make} internally uses the @code{$(SHELL)}
14348 macro to spawn shell processes and execute Make rules. This
14349 is a builtin macro supplied by @command{make}, but it can be modified
14350 by a makefile or by a command-line argument.
14352 Not all @command{make} implementations define this @code{SHELL} macro.
14354 @command{make} is an example; this implementation always uses
14355 @code{/bin/sh}. So it's a good idea to always define @code{SHELL} in
14356 your makefiles. If you use Autoconf, do
14362 Do not force @code{SHELL = /bin/sh} because that is not correct
14363 everywhere. For instance @acronym{DJGPP} lacks @code{/bin/sh}, and when
14364 its @acronym{GNU} @code{make} port sees such a setting it enters a special
14365 emulation mode where features like pipes and redirections are emulated
14366 on top of DOS's @command{command.com}. Unfortunately this emulation is
14367 incomplete; for instance it does not handle command substitutions.
14368 On @acronym{DJGPP} @code{SHELL} should point to Bash.
14370 Posix-compliant @command{make} should never acquire the value of
14371 $(SHELL) from the environment, even when @code{make -e} is used
14372 (otherwise, think about what would happen to your rules if
14373 @code{SHELL=/bin/tcsh}).
14375 However not all @command{make} implementations have this exception.
14376 For instance it's not surprising that Tru64 @command{make} doesn't
14377 protect @code{SHELL}, since it doesn't use it.
14380 $ @kbd{cat Makefile}
14386 $ @kbd{env SHELL=/bin/tcsh FOO=bar make -e} # Tru64 Make
14389 $ @kbd{env SHELL=/bin/tcsh FOO=bar gmake -e} # GNU make
14394 @node Comments in Make Rules
14395 @section Comments in Make Rules
14396 @cindex Comments in @file{Makefile} rules
14397 @cindex @file{Makefile} rules and comments
14399 Never put comments in a rule.
14401 Some @command{make} treat anything starting with a tab as a command for
14402 the current rule, even if the tab is immediately followed by a @code{#}.
14403 The @command{make} from Tru64 Unix V5.1 is one of them. The following
14404 makefile runs @code{# foo} through the shell.
14411 @node obj/ and Make
14412 @section The @file{obj/} Subdirectory and Make
14413 @cindex @file{obj/}, subdirectory
14414 @cindex @acronym{BSD} @command{make} and @file{obj/}
14416 Never name one of your subdirectories @file{obj/} if you don't like
14419 If an @file{obj/} directory exists, @acronym{BSD} @command{make} enters it
14420 before reading the makefile. Hence the makefile in the
14421 current directory is not read.
14424 $ @kbd{cat Makefile}
14427 $ @kbd{cat obj/Makefile}
14430 $ @kbd{make} # GNU make
14433 $ @kbd{pmake} # BSD make
14438 @node make -k Status
14439 @section Exit Status of @code{make -k}
14440 @cindex @code{make -k}
14442 Do not rely on the exit status of @code{make -k}. Some implementations
14443 reflect whether they encountered an error in their exit status; other
14444 implementations always succeed.
14447 $ @kbd{cat Makefile}
14450 $ @kbd{make -k; echo exit status: $?} # GNU make
14452 make: *** [all] Error 1
14454 $ @kbd{pmake -k; echo exit status: $?} # BSD make
14456 *** Error code 1 (continuing)
14460 @node VPATH and Make
14461 @section @code{VPATH} and Make
14462 @cindex @code{VPATH}
14464 Posix does not specify the semantics of @code{VPATH}. Typically,
14465 @command{make} supports @code{VPATH}, but its implementation is not
14468 Autoconf and Automake support makefiles whose usages of @code{VPATH} are
14469 portable to recent-enough popular implementations of @command{make}, but
14470 to keep the resulting makefiles portable, a package's makefile
14471 prototypes must take the following issues into account. These issues
14472 are complicated and are often poorly understood, and installers who use
14473 @code{VPATH} should expect to find many bugs in this area. If you use
14474 @code{VPATH}, the simplest way to avoid these portability bugs is to
14475 stick with @acronym{GNU} @command{make}, since it is the most
14476 commonly-used @command{make} among Autoconf users.
14478 Here are some known issues with some @code{VPATH}
14482 * VPATH and Double-colon:: Problems with @samp{::} on ancient hosts
14483 * $< in Explicit Rules:: @code{$<} does not work in ordinary rules
14484 * Automatic Rule Rewriting:: @code{VPATH} goes wild on Solaris
14485 * Tru64 Directory Magic:: @command{mkdir} goes wild on Tru64
14486 * Make Target Lookup:: More details about @code{VPATH} lookup
14489 @node VPATH and Double-colon
14490 @subsection @code{VPATH} and Double-colon Rules
14491 @cindex @code{VPATH} and double-colon rules
14492 @cindex double-colon rules and @code{VPATH}
14494 With ancient versions of Sun @command{make},
14495 any assignment to @code{VPATH} causes @command{make} to execute only
14496 the first set of double-colon rules.
14497 However, this problem is no longer of practical concern.
14499 @node $< in Explicit Rules
14500 @subsection @code{$<} Not Supported in Explicit Rules
14501 @cindex explicit rules, @code{$<}, and @code{VPATH}
14502 @cindex @code{$<}, explicit rules, and @code{VPATH}
14503 @cindex @code{VPATH}, explicit rules, and @code{$<}
14505 Using @code{$<} in explicit rules is not portable.
14506 The prerequisite file must be named explicitly in the rule. If you want
14507 to find the prerequisite via a @code{VPATH} search, you have to code the
14508 whole thing manually. @xref{Build Directories}.
14510 @node Automatic Rule Rewriting
14511 @subsection Automatic Rule Rewriting
14512 @cindex @code{VPATH} and automatic rule rewriting
14513 @cindex automatic rule rewriting and @code{VPATH}
14515 Some @command{make} implementations, such as Solaris and Tru64,
14516 search for prerequisites in @code{VPATH} and
14517 then rewrite each occurrence as a plain word in the rule.
14521 # This isn't portable to GNU make.
14528 executes @code{cp ../pkg/src/if.c f.c} if @file{if.c} is
14529 found in @file{../pkg/src}.
14531 However, this rule leads to real problems in practice. For example, if
14532 the source directory contains an ordinary file named @file{test} that is
14533 used in a dependency, Solaris @command{make} rewrites commands like
14534 @samp{if test -r foo; @dots{}} to @samp{if ../pkg/src/test -r foo;
14535 @dots{}}, which is typically undesirable. To avoid this problem,
14536 portable makefiles should never mention a source file whose name is that
14537 of a shell keyword like @file{until} or a shell command like
14538 @command{cat} or @command{gcc} or @command{test}.
14540 Because of these problems @acronym{GNU} @command{make} and many other
14541 @command{make} implementations do not rewrite commands, so portable
14543 search @code{VPATH} manually. It is tempting to write this:
14546 # This isn't portable to Solaris make.
14549 cp `test -f if.c || echo $(VPATH)/`if.c f.c
14553 However, the ``prerequisite rewriting'' still applies here. So if
14554 @file{if.c} is in @file{../pkg/src}, Solaris and Tru64 @command{make}
14558 cp `test -f ../pkg/src/if.c || echo ../pkg/src/`if.c f.c
14569 and thus fails. Oops.
14571 A simple workaround, and good practice anyway, is to use @samp{$?} and
14572 @samp{$@@} when possible:
14581 but this does not generalize well to commands with multiple
14582 prerequisites. A more general workaround is to rewrite the rule so that
14583 the prerequisite @file{if.c} never appears as a plain word. For
14584 example, these three rules would be safe, assuming @file{if.c} is in
14585 @file{../pkg/src} and the other files are in the working directory:
14590 cat `test -f ./if.c || echo $(VPATH)/`if.c f1.c >$@@
14592 cat `test -f 'if.c' || echo $(VPATH)/`if.c g1.c >$@@
14594 cat `test -f "if.c" || echo $(VPATH)/`if.c h1.c >$@@
14597 Things get worse when your prerequisites are in a macro.
14601 HEADERS = f.h g.h h.h
14602 install-HEADERS: $(HEADERS)
14603 for i in $(HEADERS); do \
14604 $(INSTALL) -m 644 \
14605 `test -f $$i || echo $(VPATH)/`$$i \
14606 $(DESTDIR)$(includedir)/$$i; \
14610 The above @code{install-HEADERS} rule is not Solaris-proof because @code{for
14611 i in $(HEADERS);} is expanded to @code{for i in f.h g.h h.h;}
14612 where @code{f.h} and @code{g.h} are plain words and are hence
14613 subject to @code{VPATH} adjustments.
14615 If the three files are in @file{../pkg/src}, the rule is run as:
14618 for i in ../pkg/src/f.h ../pkg/src/g.h h.h; do \
14620 `test -f $i || echo ../pkg/src/`$i \
14621 /usr/local/include/$i; \
14625 where the two first @command{install} calls fail. For instance,
14626 consider the @code{f.h} installation:
14630 `test -f ../pkg/src/f.h || \
14633 /usr/local/include/../pkg/src/f.h;
14642 /usr/local/include/../pkg/src/f.h;
14645 Note that the manual @code{VPATH} search did not cause any problems here;
14646 however this command installs @file{f.h} in an incorrect directory.
14648 Trying to quote @code{$(HEADERS)} in some way, as we did for
14649 @code{foo.c} a few makefiles ago, does not help:
14652 install-HEADERS: $(HEADERS)
14653 headers='$(HEADERS)'; \
14654 for i in $$headers; do \
14655 $(INSTALL) -m 644 \
14656 `test -f $$i || echo $(VPATH)/`$$i \
14657 $(DESTDIR)$(includedir)/$$i; \
14661 Now, @code{headers='$(HEADERS)'} macro-expands to:
14664 headers='f.h g.h h.h'
14668 but @code{g.h} is still a plain word. (As an aside, the idiom
14669 @code{headers='$(HEADERS)'; for i in $$headers;} is a good
14670 idea if @code{$(HEADERS)} can be empty, because some shells diagnose a
14671 syntax error on @code{for i in;}.)
14673 One workaround is to strip this unwanted @file{../pkg/src/} prefix manually:
14677 HEADERS = f.h g.h h.h
14678 install-HEADERS: $(HEADERS)
14679 headers='$(HEADERS)'; \
14680 for i in $$headers; do \
14681 i=`expr "$$i" : '$(VPATH)/\(.*\)'`;
14682 $(INSTALL) -m 644 \
14683 `test -f $$i || echo $(VPATH)/`$$i \
14684 $(DESTDIR)$(includedir)/$$i; \
14688 Automake does something similar. However the above hack works only if
14689 the files listed in @code{HEADERS} are in the current directory or a
14690 subdirectory; they should not be in an enclosing directory. If we had
14691 @code{HEADERS = ../f.h}, the above fragment would fail in a VPATH
14692 build with Tru64 @command{make}. The reason is that not only does
14693 Tru64 @command{make} rewrite dependencies, but it also simplifies
14694 them. Hence @code{../f.h} becomes @code{../pkg/f.h} instead of
14695 @code{../pkg/src/../f.h}. This obviously defeats any attempt to strip
14696 a leading @file{../pkg/src/} component.
14698 The following example makes the behavior of Tru64 @command{make}
14702 $ @kbd{cat Makefile}
14714 Dependency @file{../foo} was found in @file{sub/../foo}, but Tru64
14715 @command{make} simplified it as @file{foo}. (Note that the @file{sub/}
14716 directory does not even exist, this just means that the simplification
14717 occurred before the file was checked for.)
14719 For the record here is how SunOS 4 @command{make} behaves on this
14724 make: Fatal error: Don't know how to make target `../foo'
14732 @node Tru64 Directory Magic
14733 @subsection Tru64 @command{make} Creates Prerequisite Directories Magically
14734 @cindex @code{VPATH} and prerequisite directories
14735 @cindex prerequisite directories and @code{VPATH}
14737 When a prerequisite is a subdirectory of @code{VPATH}, Tru64
14738 @command{make} creates it in the current directory.
14741 $ @kbd{mkdir -p foo/bar build}
14743 $ @kbd{cat >Makefile <<END
14752 This can yield unexpected results if a rule uses a manual @code{VPATH}
14753 search as presented before.
14758 command `test -d foo/bar || echo ../`foo/bar
14761 The above @command{command} is run on the empty @file{foo/bar}
14762 directory that was created in the current directory.
14764 @node Make Target Lookup
14765 @subsection Make Target Lookup
14766 @cindex @code{VPATH}, resolving target pathnames
14768 @acronym{GNU} @command{make} uses a complex algorithm to decide when it
14769 should use files found via a @code{VPATH} search. @xref{Search
14770 Algorithm, , How Directory Searches are Performed, make, The @acronym{GNU} Make
14773 If a target needs to be rebuilt, @acronym{GNU} @command{make} discards the
14774 file name found during the @code{VPATH} search for this target, and
14775 builds the file locally using the file name given in the makefile.
14776 If a target does not need to be rebuilt, @acronym{GNU} @command{make} uses the
14777 file name found during the @code{VPATH} search.
14779 Other @command{make} implementations, like Net@acronym{BSD} @command{make}, are
14780 easier to describe: the file name found during the @code{VPATH} search
14781 is used whether the target needs to be rebuilt or not. Therefore
14782 new files are created locally, but existing files are updated at their
14783 @code{VPATH} location.
14785 Open@acronym{BSD} and Free@acronym{BSD} @command{make}, however,
14787 @code{VPATH} search for a dependency that has an explicit rule.
14788 This is extremely annoying.
14790 When attempting a @code{VPATH} build for an autoconfiscated package
14791 (e.g., @code{mkdir build && cd build && ../configure}), this means
14793 @command{make} builds everything locally in the @file{build}
14794 directory, while @acronym{BSD} @command{make} builds new files locally and
14795 updates existing files in the source directory.
14798 $ @kbd{cat Makefile}
14801 foo.x bar.x: newer.x
14802 @@echo Building $@@
14803 $ @kbd{touch ../bar.x}
14804 $ @kbd{touch ../newer.x}
14805 $ @kbd{make} # GNU make
14808 $ @kbd{pmake} # NetBSD make
14811 $ @kbd{fmake} # FreeBSD make, OpenBSD make
14814 $ @kbd{tmake} # Tru64 make
14817 $ @kbd{touch ../bar.x}
14818 $ @kbd{make} # GNU make
14820 $ @kbd{pmake} # NetBSD make
14822 $ @kbd{fmake} # FreeBSD make, OpenBSD make
14825 $ @kbd{tmake} # Tru64 make
14830 Note how Net@acronym{BSD} @command{make} updates @file{../bar.x} in its
14831 VPATH location, and how Free@acronym{BSD}, Open@acronym{BSD}, and Tru64
14832 @command{make} always
14833 update @file{bar.x}, even when @file{../bar.x} is up to date.
14835 Another point worth mentioning is that once @acronym{GNU} @command{make} has
14836 decided to ignore a @code{VPATH} file name (e.g., it ignored
14837 @file{../bar.x} in the above example) it continues to ignore it when
14838 the target occurs as a prerequisite of another rule.
14840 The following example shows that @acronym{GNU} @command{make} does not look up
14841 @file{bar.x} in @code{VPATH} before performing the @code{.x.y} rule,
14842 because it ignored the @code{VPATH} result of @file{bar.x} while running
14843 the @code{bar.x: newer.x} rule.
14846 $ @kbd{cat Makefile}
14850 @@echo Building $@@
14854 $ @kbd{touch ../bar.x}
14855 $ @kbd{touch ../newer.x}
14856 $ @kbd{make} # GNU make
14859 cp: cannot stat `bar.x': No such file or directory
14860 make: *** [bar.y] Error 1
14861 $ @kbd{pmake} # NetBSD make
14865 $ @kbd{fmake} # FreeBSD make, OpenBSD make
14866 echo Building bar.x
14868 cp: cannot stat `bar.x': No such file or directory
14870 $ @kbd{tmake} # Tru64 make
14872 cp: bar.x: No such file or directory
14876 Note that if you drop away the command from the @code{bar.x: newer.x}
14877 rule, @acronym{GNU} @command{make} magically starts to work: it
14878 knows that @code{bar.x} hasn't been updated, therefore it doesn't
14879 discard the result from @code{VPATH} (@file{../bar.x}) in succeeding
14880 uses. Tru64 also works, but Free@acronym{BSD} and Open@acronym{BSD}
14884 $ @kbd{cat Makefile}
14891 $ @kbd{touch ../bar.x}
14892 $ @kbd{touch ../newer.x}
14893 $ @kbd{make} # GNU make
14896 $ @kbd{pmake} # NetBSD make
14899 $ @kbd{fmake} # FreeBSD make, OpenBSD make
14901 cp: cannot stat `bar.x': No such file or directory
14903 $ @kbd{tmake} # Tru64 make
14907 It seems the sole solution that would please every @command{make}
14908 implementation is to never rely on @code{VPATH} searches for targets.
14909 In other words, @code{VPATH} should be reserved to unbuilt sources.
14912 @node Single Suffix Rules
14913 @section Single Suffix Rules and Separated Dependencies
14914 @cindex Single Suffix Inference Rule
14915 @cindex Rule, Single Suffix Inference
14916 A @dfn{Single Suffix Rule} is basically a usual suffix (inference) rule
14917 (@samp{.from.to:}), but which @emph{destination} suffix is empty
14920 @cindex Separated Dependencies
14921 @dfn{Separated dependencies} simply refers to listing the prerequisite
14922 of a target, without defining a rule. Usually one can list on the one
14923 hand side, the rules, and on the other hand side, the dependencies.
14925 Solaris @command{make} does not support separated dependencies for
14926 targets defined by single suffix rules:
14929 $ @kbd{cat Makefile}
14934 $ @kbd{touch foo.in}
14941 while @acronym{GNU} Make does:
14947 Makefile foo foo.in
14950 Note it works without the @samp{foo: foo.in} dependency.
14953 $ @kbd{cat Makefile}
14962 and it works with double suffix inference rules:
14965 $ @kbd{cat Makefile}
14967 .SUFFIXES: .in .out
14974 As a result, in such a case, you have to write target rules.
14976 @node Timestamps and Make
14977 @section Timestamp Resolution and Make
14978 @cindex timestamp resolution
14979 Traditionally, file timestamps had 1-second resolution, and
14980 @command{make} used those timestamps to determine whether one file was
14981 newer than the other. However, many modern file systems have
14982 timestamps with 1-nanosecond resolution. Some @command{make}
14983 implementations look at the entire timestamp; others ignore the
14984 fractional part, which can lead to incorrect results. Normally this
14985 is not a problem, but in some extreme cases you may need to use tricks
14986 like @samp{sleep 1} to work around timestamp truncation bugs.
14988 Commands like @samp{cp -p} and @samp{touch -r} typically do not copy
14989 file timestamps to their full resolutions (@pxref{Limitations of Usual
14990 Tools}). Hence you should be wary of rules like this:
14997 as @file{dest} often appears to be older than @file{src} after the
14998 timestamp is truncated, and this can cause @command{make} to do
14999 needless rework the next time it is invoked. To work around this
15000 problem, you can use a timestamp file, e.g.:
15011 @c ======================================== Portable C and C++ Programming
15013 @node Portable C and C++
15014 @chapter Portable C and C++ Programming
15015 @cindex Portable C and C++ programming
15017 C and C++ programs often use low-level features of the underlying
15018 system, and therefore are often more difficult to make portable to other
15021 Several standards have been developed to help make your programs more
15022 portable. If you write programs with these standards in mind, you can
15023 have greater confidence that your programs work on a wide variety
15024 of systems. @xref{Standards, , Language Standards Supported by
15025 @acronym{GCC}, gcc, Using the @acronym{GNU} Compiler Collection
15026 (@acronym{GCC})}, for a list of C-related
15027 standards. Many programs also assume the
15028 @uref{http://www.opengroup.org/susv3, Posix standard}.
15030 Some old code is written to be portable to K&R C, which predates any C
15031 standard. K&R C compilers are no longer of practical interest, though,
15032 and the rest of section assumes at least C89, the first C standard.
15034 Program portability is a huge topic, and this section can only briefly
15035 introduce common pitfalls. @xref{System Portability, , Portability
15036 between System Types, standards, @acronym{GNU} Coding Standards}, for
15040 * Varieties of Unportability:: How to make your programs unportable
15041 * Integer Overflow:: When integers get too large
15042 * Null Pointers:: Properties of null pointers
15043 * Buffer Overruns:: Subscript errors and the like
15044 * Volatile Objects:: @code{volatile} and signals
15045 * Floating Point Portability:: Portable floating-point arithmetic
15046 * Exiting Portably:: Exiting and the exit status
15049 @node Varieties of Unportability
15050 @section Varieties of Unportability
15051 @cindex portability
15053 Autoconf tests and ordinary programs often need to test what is allowed
15054 on a system, and therefore they may need to deliberately exceed the
15055 boundaries of what the standards allow, if only to see whether an
15056 optional feature is present. When you write such a program, you should
15057 keep in mind the difference between constraints, unspecified behavior,
15058 and undefined behavior.
15060 In C, a @dfn{constraint} is a rule that the compiler must enforce. An
15061 example constraint is that C programs must not declare a bit-field with
15062 negative width. Tests can therefore reliably assume that programs with
15063 negative-width bit-fields are rejected by a compiler that conforms
15066 @dfn{Unspecified behavior} is valid behavior, where the standard allows
15067 multiple possibilities. For example, the order of evaluation of
15068 function arguments is unspecified. Some unspecified behavior is
15069 @dfn{implementation-defined}, i.e., documented by the implementation,
15070 but since Autoconf tests cannot read the documentation they cannot
15071 distinguish between implementation-defined and other unspecified
15072 behavior. It is common for Autoconf tests to probe implementations to
15073 determine otherwise-unspecified behavior.
15075 @dfn{Undefined behavior} is invalid behavior, where the standard allows
15076 the implementation to do anything it pleases. For example,
15077 dereferencing a null pointer leads to undefined behavior. If possible,
15078 test programs should avoid undefined behavior, since a program with
15079 undefined behavior might succeed on a test that should fail.
15081 The above rules apply to programs that are intended to conform to the
15082 standard. However, strictly-conforming programs are quite rare, since
15083 the standards are so limiting. A major goal of Autoconf is to support
15084 programs that use implementation features not described by the standard,
15085 and it is fairly common for test programs to violate the above rules, if
15086 the programs work well enough in practice.
15088 @node Integer Overflow
15089 @section Integer Overflow
15090 @cindex integer overflow
15091 @cindex overflow, signed integer
15092 @cindex signed integer overflow
15093 @cindex wraparound arithmetic
15095 In practice many portable C programs assume that signed integer overflow wraps
15096 around reliably using two's complement arithmetic. Yet the C standard
15097 says that program behavior is undefined on overflow, and in a few cases
15098 C programs do not work on some modern implementations because their
15099 overflows do not wrap around as their authors expected. Conversely, in
15100 signed integer remainder, the C standard requires overflow
15101 behavior that is commonly not implemented.
15104 * Integer Overflow Basics:: Why integer overflow is a problem
15105 * Signed Overflow Examples:: Examples of code assuming wraparound
15106 * Optimization and Wraparound:: Optimizations that break uses of wraparound
15107 * Signed Overflow Advice:: Practical advice for signed overflow issues
15108 * Signed Integer Division:: @code{INT_MIN / -1} and @code{INT_MIN % -1}
15111 @node Integer Overflow Basics
15112 @subsection Basics of Integer Overflow
15113 @cindex integer overflow
15114 @cindex overflow, signed integer
15115 @cindex signed integer overflow
15116 @cindex wraparound arithmetic
15118 In languages like C, unsigned integer overflow reliably wraps around;
15119 e.g., @code{UINT_MAX + 1} yields zero.
15120 This is guaranteed by the C standard and is
15121 portable in practice, unless you specify aggressive,
15122 nonstandard optimization options
15123 suitable only for special applications.
15125 In contrast, the C standard says that signed integer overflow leads to
15126 undefined behavior where a program can do anything, including dumping
15127 core or overrunning a buffer. The misbehavior can even precede the
15128 overflow. Such an overflow can occur during addition, subtraction,
15129 multiplication, division, and left shift.
15131 Despite this requirement of the standard, many C programs and Autoconf
15132 tests assume that signed integer overflow silently wraps around modulo a
15133 power of two, using two's complement arithmetic, so long as you cast the
15134 resulting value to a signed integer type or store it into a signed
15135 integer variable. If you use conservative optimization flags, such
15136 programs are generally portable to the vast majority of modern
15137 platforms, with a few exceptions discussed later.
15139 For historical reasons the C standard also allows implementations with
15140 ones' complement or signed magnitude arithmetic, but it is safe to
15141 assume two's complement nowadays.
15143 Also, overflow can occur when converting an out-of-range value to a
15144 signed integer type. Here a standard implementation must define what
15145 happens, but this might include raising an exception. In practice all
15146 known implementations support silent wraparound in this case, so you need
15147 not worry about other possibilities.
15149 @node Signed Overflow Examples
15150 @subsection Examples of Code Assuming Wraparound Overflow
15151 @cindex integer overflow
15152 @cindex overflow, signed integer
15153 @cindex signed integer overflow
15154 @cindex wraparound arithmetic
15156 There has long been a tension between what the C standard requires for
15157 signed integer overflow, and what C programs commonly assume. The
15158 standard allows aggressive optimizations based on assumptions that
15159 overflow never occurs, but many practical C programs rely on overflow
15160 wrapping around. These programs do not conform to the standard, but
15161 they commonly work in practice because compiler writers are
15162 understandably reluctant to implement optimizations that would break
15163 many programs, unless perhaps a user specifies aggressive optimization.
15165 The C Standard says that if a program has signed integer overflow its
15166 behavior is undefined, and the undefined behavior can even precede the
15167 overflow. To take an extreme example:
15169 @c Inspired by Robert Dewar's example in
15170 @c <http://gcc.gnu.org/ml/gcc/2007-01/msg00038.html> (2007-01-01).
15172 if (password == expected_password)
15173 allow_superuser_privileges ();
15174 else if (counter++ == INT_MAX)
15177 printf ("%d password mismatches\n", counter);
15181 If the @code{int} variable @code{counter} equals @code{INT_MAX},
15182 @code{counter++} must overflow and the behavior is undefined, so the C
15183 standard allows the compiler to optimize away the test against
15184 @code{INT_MAX} and the @code{abort} call.
15185 Worse, if an earlier bug in the program lets the compiler deduce that
15186 @code{counter == INT_MAX} or that @code{counter} previously overflowed,
15187 the C standard allows the compiler to optimize away the password test
15188 and generate code that allows superuser privileges unconditionally.
15190 Despite this requirement by the standard, it has long been common for C
15191 code to assume wraparound arithmetic after signed overflow, and all
15192 known practical C implementations support some C idioms that assume
15193 wraparound signed arithmetic, even if the idioms do not conform
15194 strictly to the standard. If your code looks like the following
15195 examples it will almost surely work with real-world compilers.
15197 Here is an example derived from the 7th Edition Unix implementation of
15198 @code{atoi} (1979-01-10):
15204 while (*p >= '0' && *p <= '9')
15205 n = n * 10 + *p++ - '0';
15206 return (f ? -n : n);
15210 Even if the input string is in range, on most modern machines this has
15211 signed overflow when computing the most negative integer (the @code{-n}
15212 overflows) or a value near an extreme integer (the first @code{+}
15215 Here is another example, derived from the 7th Edition implementation of
15216 @code{rand} (1979-01-10). Here the programmer expects both
15217 multiplication and addition to wrap on overflow:
15220 static long int randx = 1;
15222 randx = randx * 1103515245 + 12345;
15223 return (randx >> 16) & 077777;
15226 In the following example, derived from the @acronym{GNU} C Library 2.5
15227 implementation of @code{mktime} (2006-09-09), the code assumes
15228 wraparound arithmetic in @code{+} to detect signed overflow:
15232 int sec_requested, sec_adjustment;
15234 t1 = t + sec_requested;
15235 t2 = t1 + sec_adjustment;
15236 if (((t1 < t) != (sec_requested < 0))
15237 | ((t2 < t1) != (sec_adjustment < 0)))
15241 If your code looks like these examples, it is probably safe even though
15242 it does not strictly conform to the C standard. This might lead one to
15243 believe that one can generally assume wraparound on overflow, but that
15244 is not always true, as can be seen in the next section.
15246 @node Optimization and Wraparound
15247 @subsection Optimizations That Break Wraparound Arithmetic
15248 @cindex loop induction
15250 Compilers sometimes generate code that is incompatible with wraparound
15251 integer arithmetic. A simple example is an algebraic simplification: a
15252 compiler might translate @code{(i * 2000) / 1000} to @code{i * 2}
15253 because it assumes that @code{i * 2000} does not overflow. The
15254 translation is not equivalent to the original when overflow occurs:
15255 e.g., in the typical case of 32-bit signed two's complement wraparound
15256 @code{int}, if @code{i} has type @code{int} and value @code{1073742},
15257 the original expression returns @minus{}2147483 but the optimized
15258 version returns the mathematically correct value 2147484.
15260 More subtly, loop induction optimizations often exploit the undefined
15261 behavior of signed overflow. Consider the following contrived function
15266 sumc (int lo, int hi)
15270 for (i = lo; i <= hi; i++)
15277 To avoid multiplying by 53 each time through the loop, an optimizing
15278 compiler might internally transform @code{sumc} to the equivalent of the
15283 transformed_sumc (int lo, int hi)
15288 for (ic = lo * 53; ic <= hic; ic += 53)
15295 This transformation is allowed by the C standard, but it is invalid for
15296 wraparound arithmetic when @code{INT_MAX / 53 < hi}, because then the
15297 overflow in computing expressions like @code{hi * 53} can cause the
15298 expression @code{i <= hi} to yield a different value from the
15299 transformed expression @code{ic <= hic}.
15301 For this reason, compilers that use loop induction and similar
15302 techniques often do not support reliable wraparound arithmetic when a
15303 loop induction variable like @code{ic} is involved. Since loop
15304 induction variables are generated by the compiler, and are not visible
15305 in the source code, it is not always trivial to say whether the problem
15308 Hardly any code actually depends on wraparound arithmetic in cases like
15309 these, so in practice these loop induction optimizations are almost
15310 always useful. However, edge cases in this area can cause problems.
15315 for (j = 1; 0 < j; j *= 2)
15320 Here, the loop attempts to iterate through all powers of 2 that
15321 @code{int} can represent, but the C standard allows a compiler to
15322 optimize away the comparison and generate an infinite loop,
15323 under the argument that behavior is undefined on overflow. As of this
15324 writing this optimization is not done by any production version of
15325 @acronym{GCC} with @option{-O2}, but it might be performed by other
15326 compilers, or by more aggressive @acronym{GCC} optimization options,
15327 and the @acronym{GCC} developers have not decided whether it will
15328 continue to work with @acronym{GCC} and @option{-O2}.
15330 @node Signed Overflow Advice
15331 @subsection Practical Advice for Signed Overflow Issues
15332 @cindex integer overflow
15333 @cindex overflow, signed integer
15334 @cindex signed integer overflow
15335 @cindex wraparound arithmetic
15337 Ideally the safest approach is to avoid signed integer overflow
15338 entirely. For example, instead of multiplying two signed integers, you
15339 can convert them to unsigned integers, multiply the unsigned values,
15340 then test whether the result is in signed range.
15342 Rewriting code in this way will be inconvenient, though, particularly if
15343 the signed values might be negative. Also, it may hurt
15344 performance. Using unsigned arithmetic to check for overflow is
15345 particularly painful to do portably and efficiently when dealing with an
15346 integer type like @code{uid_t} whose width and signedness vary from
15347 platform to platform.
15349 Furthermore, many C applications pervasively assume wraparound behavior
15350 and typically it is not easy to find and remove all these assumptions.
15351 Hence it is often useful to maintain nonstandard code that assumes
15352 wraparound on overflow, instead of rewriting the code. The rest of this
15353 section attempts to give practical advice for this situation.
15355 If your code wants to detect signed integer overflow in @code{sum = a +
15356 b}, it is generally safe to use an expression like @code{(sum < a) != (b
15359 If your code uses a signed loop index, make sure that the index cannot
15360 overflow, along with all signed expressions derived from the index.
15361 Here is a contrived example of problematic code with two instances of
15365 for (i = INT_MAX - 10; i <= INT_MAX; i++)
15368 report_overflow ();
15374 Because of the two overflows, a compiler might optimize away or
15375 transform the two comparisons in a way that is incompatible with the
15376 wraparound assumption.
15378 If your code uses an expression like @code{(i * 2000) / 1000} and you
15379 actually want the multiplication to wrap around on overflow, use
15380 unsigned arithmetic
15381 to do it, e.g., @code{((int) (i * 2000u)) / 1000}.
15383 If your code assumes wraparound behavior and you want to insulate it
15384 against any @acronym{GCC} optimizations that would fail to support that
15385 behavior, you should use @acronym{GCC}'s @option{-fwrapv} option, which
15386 causes signed overflow to wrap around reliably (except for division and
15387 remainder, as discussed in the next section).
15389 If you need to port to platforms where signed integer overflow does not
15390 reliably wrap around (e.g., due to hardware overflow checking, or to
15391 highly aggressive optimizations), you should consider debugging with
15392 @acronym{GCC}'s @option{-ftrapv} option, which causes signed overflow to
15393 raise an exception.
15395 @node Signed Integer Division
15396 @subsection Signed Integer Division and Integer Overflow
15397 @cindex division, integer
15400 integer division is not always harmless: for example, on CPUs of the
15401 i386 family, dividing @code{INT_MIN} by @code{-1} yields a SIGFPE signal
15402 which by default terminates the program. Worse, taking the remainder
15403 of these two values typically yields the same signal on these CPUs,
15404 even though the C standard requires @code{INT_MIN % -1} to yield zero
15405 because the expression does not overflow.
15407 @node Null Pointers
15408 @section Properties of Null Pointers
15409 @cindex null pointers
15411 Most modern hosts reliably fail when you attempt to dereference a null
15414 On almost all modern hosts, null pointers use an all-bits-zero internal
15415 representation, so you can reliably use @code{memset} with 0 to set all
15416 the pointers in an array to null values.
15418 If @code{p} is a null pointer to an object type, the C expression
15419 @code{p + 0} always evaluates to @code{p} on modern hosts, even though
15420 the standard says that it has undefined behavior.
15422 @node Buffer Overruns
15423 @section Buffer Overruns and Subscript Errors
15424 @cindex buffer overruns
15426 Buffer overruns and subscript errors are the most common dangerous
15427 errors in C programs. They result in undefined behavior because storing
15428 outside an array typically modifies storage that is used by some other
15429 object, and most modern systems lack runtime checks to catch these
15430 errors. Programs should not rely on buffer overruns being caught.
15432 There is one exception to the usual rule that a portable program cannot
15433 address outside an array. In C, it is valid to compute the address just
15434 past an object, e.g., @code{&a[N]} where @code{a} has @code{N} elements,
15435 so long as you do not dereference the resulting pointer. But it is not
15436 valid to compute the address just before an object, e.g., @code{&a[-1]};
15437 nor is it valid to compute two past the end, e.g., @code{&a[N+1]}. On
15438 most platforms @code{&a[-1] < &a[0] && &a[N] < &a[N+1]}, but this is not
15439 reliable in general, and it is usually easy enough to avoid the
15440 potential portability problem, e.g., by allocating an extra unused array
15441 element at the start or end.
15443 @uref{http://valgrind.org/, Valgrind} can catch many overruns.
15445 users might also consider using the @option{-fmudflap} option to catch
15448 Buffer overruns are usually caused by off-by-one errors, but there are
15449 more subtle ways to get them.
15451 Using @code{int} values to index into an array or compute array sizes
15452 causes problems on typical 64-bit hosts where an array index might
15453 be @math{2^31} or larger. Index values of type @code{size_t} avoid this
15454 problem, but cannot be negative. Index values of type @code{ptrdiff_t}
15455 are signed, and are wide enough in practice.
15457 If you add or multiply two numbers to calculate an array size, e.g.,
15458 @code{malloc (x * sizeof y + z)}, havoc ensues if the addition or
15459 multiplication overflows.
15461 Many implementations of the @code{alloca} function silently misbehave
15462 and can generate buffer overflows if given sizes that are too large.
15463 The size limits are implementation dependent, but are at least 4000
15464 bytes on all platforms that we know about.
15466 The standard functions @code{asctime}, @code{asctime_r}, @code{ctime},
15467 @code{ctime_r}, and @code{gets} are prone to buffer overflows, and
15468 portable code should not use them unless the inputs are known to be
15469 within certain limits. The time-related functions can overflow their
15470 buffers if given timestamps out of range (e.g., a year less than -999
15471 or greater than 9999). Time-related buffer overflows cannot happen with
15472 recent-enough versions of the @acronym{GNU} C library, but are possible
15474 implementations. The @code{gets} function is the worst, since it almost
15475 invariably overflows its buffer when presented with an input line larger
15478 @node Volatile Objects
15479 @section Volatile Objects
15480 @cindex volatile objects
15482 The keyword @code{volatile} is often misunderstood in portable code.
15483 Its use inhibits some memory-access optimizations, but programmers often
15484 wish that it had a different meaning than it actually does.
15486 @code{volatile} was designed for code that accesses special objects like
15487 memory-mapped device registers whose contents spontaneously change.
15488 Such code is inherently low-level, and it is difficult to specify
15489 portably what @code{volatile} means in these cases. The C standard
15490 says, ``What constitutes an access to an object that has
15491 volatile-qualified type is implementation-defined,'' so in theory each
15492 implementation is supposed to fill in the gap by documenting what
15493 @code{volatile} means for that implementation. In practice, though,
15494 this documentation is usually absent or incomplete.
15496 One area of confusion is the distinction between objects defined with
15497 volatile types, and volatile lvalues. From the C standard's point of
15498 view, an object defined with a volatile type has externally visible
15499 behavior. You can think of such objects as having little oscilloscope
15500 probes attached to them, so that the user can observe some properties of
15501 accesses to them, just as the user can observe data written to output
15502 files. However, the standard does not make it clear whether users can
15503 observe accesses by volatile lvalues to ordinary objects. For example:
15506 /* Declare and access a volatile object.
15507 Accesses to X are "visible" to users. */
15508 static int volatile x;
15511 /* Access two ordinary objects via a volatile lvalue.
15512 It's not clear whether accesses to *P are "visible". */
15514 int *z = malloc (sizeof (int));
15522 Programmers often wish that @code{volatile} meant ``Perform the memory
15523 access here and now, without merging several memory accesses, without
15524 changing the memory word size, and without reordering.'' But the C
15525 standard does not require this. For objects defined with a volatile
15526 type, accesses must be done before the next sequence point; but
15527 otherwise merging, reordering, and word-size change is allowed. Worse,
15528 it is not clear from the standard whether volatile lvalues provide more
15529 guarantees in general than nonvolatile lvalues, if the underlying
15530 objects are ordinary.
15532 Even when accessing objects defined with a volatile type,
15533 the C standard allows only
15534 extremely limited signal handlers: the behavior is undefined if a signal
15535 handler reads any nonlocal object, or writes to any nonlocal object
15536 whose type is not @code{sig_atomic_t volatile}, or calls any standard
15537 library function other than @code{abort}, @code{signal}, and (if C99)
15538 @code{_Exit}. Hence C compilers need not worry about a signal handler
15539 disturbing ordinary computation, unless the computation accesses a
15540 @code{sig_atomic_t volatile} lvalue that is not a local variable.
15541 (There is an obscure exception for accesses via a pointer to a volatile
15542 character, since it may point into part of a @code{sig_atomic_t
15543 volatile} object.) Posix
15544 adds to the list of library functions callable from a portable signal
15545 handler, but otherwise is like the C standard in this area.
15547 Some C implementations allow memory-access optimizations within each
15548 translation unit, such that actual behavior agrees with the behavior
15549 required by the standard only when calling a function in some other
15550 translation unit, and a signal handler acts like it was called from a
15551 different translation unit. The C standard hints that in these
15552 implementations, objects referred to by signal handlers ``would require
15553 explicit specification of @code{volatile} storage, as well as other
15554 implementation-defined restrictions.'' But unfortunately even for this
15555 special case these other restrictions are often not documented well.
15556 @xref{Volatiles, , When is a Volatile Object Accessed?, gcc, Using the
15557 @acronym{GNU} Compiler Collection (@acronym{GCC})}, for some
15558 restrictions imposed by @acronym{GCC}. @xref{Defining Handlers, ,
15559 Defining Signal Handlers, libc, The @acronym{GNU} C Library}, for some
15560 restrictions imposed by the @acronym{GNU} C library. Restrictions
15561 differ on other platforms.
15563 If possible, it is best to use a signal handler that fits within the
15564 limits imposed by the C and Posix standards.
15566 If this is not practical, you can try the following rules of thumb. A
15567 signal handler should access only volatile lvalues, preferably lvalues
15568 that refer to objects defined with a volatile type, and should not
15569 assume that the accessed objects have an internally consistent state
15570 if they are larger than a machine word. Furthermore, installers
15571 should employ compilers and compiler options that are commonly used
15572 for building operating system kernels, because kernels often need more
15573 from @code{volatile} than the C Standard requires, and installers who
15574 compile an application in a similar environment can sometimes benefit
15575 from the extra constraints imposed by kernels on compilers.
15576 Admittedly we are handwaving somewhat here, as there are few
15577 guarantees in this area; the rules of thumb may help to fix some bugs
15578 but there is a good chance that they will not fix them all.
15580 For @code{volatile}, C++ has the same problems that C does.
15581 Multithreaded applications have even more problems with @code{volatile},
15582 but they are beyond the scope of this section.
15584 The bottom line is that using @code{volatile} typically hurts
15585 performance but should not hurt correctness. In some cases its use
15586 does help correctness, but these cases are often so poorly understood
15587 that all too often adding @code{volatile} to a data structure merely
15588 alleviates some symptoms of a bug while not fixing the bug in general.
15590 @node Floating Point Portability
15591 @section Floating Point Portability
15592 @cindex floating point
15594 Almost all modern systems use IEEE-754 floating point, and it is safe to
15595 assume IEEE-754 in most portable code these days. For more information,
15596 please see David Goldberg's classic paper
15597 @uref{http://www.validlab.com/goldberg/paper.pdf, What Every Computer
15598 Scientist Should Know About Floating-Point Arithmetic}.
15600 @node Exiting Portably
15601 @section Exiting Portably
15602 @cindex exiting portably
15604 A C or C++ program can exit with status @var{N} by returning
15605 @var{N} from the @code{main} function. Portable programs are supposed
15606 to exit either with status 0 or @code{EXIT_SUCCESS} to succeed, or with
15607 status @code{EXIT_FAILURE} to fail, but in practice it is portable to
15608 fail by exiting with status 1, and test programs that assume Posix can
15609 fail by exiting with status values from 1 through 255. Programs on
15610 SunOS 2.0 (1985) through 3.5.2 (1988) incorrectly exited with zero
15611 status when @code{main} returned nonzero, but ancient systems like these
15612 are no longer of practical concern.
15614 A program can also exit with status @var{N} by passing @var{N} to the
15615 @code{exit} function, and a program can fail by calling the @code{abort}
15616 function. If a program is specialized to just some platforms, it can fail
15617 by calling functions specific to those platforms, e.g., @code{_exit}
15618 (Posix) and @code{_Exit} (C99). However, like other functions, an exit
15619 function should be declared, typically by including a header. For
15620 example, if a C program calls @code{exit}, it should include @file{stdlib.h}
15621 either directly or via the default includes (@pxref{Default Includes}).
15623 A program can fail due to undefined behavior such as dereferencing a null
15624 pointer, but this is not recommended as undefined behavior allows an
15625 implementation to do whatever it pleases and this includes exiting
15629 @c ================================================== Manual Configuration
15631 @node Manual Configuration
15632 @chapter Manual Configuration
15634 A few kinds of features can't be guessed automatically by running test
15635 programs. For example, the details of the object-file format, or
15636 special options that need to be passed to the compiler or linker. You
15637 can check for such features using ad-hoc means, such as having
15638 @command{configure} check the output of the @code{uname} program, or
15639 looking for libraries that are unique to particular systems. However,
15640 Autoconf provides a uniform method for handling unguessable features.
15643 * Specifying Names:: Specifying the system type
15644 * Canonicalizing:: Getting the canonical system type
15645 * Using System Type:: What to do with the system type
15648 @node Specifying Names
15649 @section Specifying the System Type
15650 @cindex System type
15653 @command{configure} scripts can make decisions based on a canonical name
15654 for the system type, which has the form:
15655 @samp{@var{cpu}-@var{vendor}-@var{os}}, where @var{os} can be
15656 @samp{@var{system}} or @samp{@var{kernel}-@var{system}}
15658 @command{configure} can usually guess the canonical name for the type of
15659 system it's running on. To do so it runs a script called
15660 @command{config.guess}, which infers the name using the @code{uname}
15661 command or symbols predefined by the C preprocessor.
15663 Alternately, the user can specify the system type with command line
15664 arguments to @command{configure}. Doing so is necessary when
15665 cross-compiling. In the most complex case of cross-compiling, three
15666 system types are involved. The options to specify them are:
15669 @item --build=@var{build-type}
15670 the type of system on which the package is being configured and
15671 compiled. It defaults to the result of running @command{config.guess}.
15673 @item --host=@var{host-type}
15674 the type of system on which the package runs. By default it is the
15675 same as the build machine. Specifying it enables the cross-compilation
15678 @item --target=@var{target-type}
15679 the type of system for which any compiler tools in the package
15680 produce code (rarely needed). By default, it is the same as host.
15683 If you mean to override the result of @command{config.guess}, use
15684 @option{--build}, not @option{--host}, since the latter enables
15685 cross-compilation. For historical reasons,
15686 whenever you specify @option{--host},
15687 be sure to specify @option{--build} too; this will be fixed in the
15688 future. So, to enter cross-compilation mode, use a command like this
15691 ./configure --build=i686-pc-linux-gnu --host=m68k-coff
15695 Note that if you do not specify @option{--host}, @command{configure}
15696 fails if it can't run the code generated by the specified compiler. For
15697 example, configuring as follows fails:
15700 ./configure CC=m68k-coff-gcc
15703 In the future, when cross-compiling Autoconf will @emph{not}
15704 accept tools (compilers, linkers, assemblers) whose name is not
15705 prefixed with the host type. The only case when this may be
15706 useful is when you really are not cross-compiling, but only
15707 building for a least-common-denominator architecture: an example
15708 is building for @code{i386-pc-linux-gnu} while running on an
15709 @code{i686-pc-linux-gnu} architecture. In this case, some particular
15710 pairs might be similar enough to let you get away with the system
15711 compilers, but in general the compiler might make bogus assumptions
15712 on the host: if you know what you are doing, please create symbolic
15713 links from the host compiler to the build compiler.
15715 @cindex @command{config.sub}
15716 @command{configure} recognizes short aliases for many system types; for
15717 example, @samp{decstation} can be used instead of
15718 @samp{mips-dec-ultrix4.2}. @command{configure} runs a script called
15719 @command{config.sub} to canonicalize system type aliases.
15721 This section deliberately omits the description of the obsolete
15722 interface; see @ref{Hosts and Cross-Compilation}.
15725 @node Canonicalizing
15726 @section Getting the Canonical System Type
15727 @cindex System type
15728 @cindex Canonical system type
15730 The following macros make the system type available to @command{configure}
15733 @ovindex build_alias
15734 @ovindex host_alias
15735 @ovindex target_alias
15737 The variables @samp{build_alias}, @samp{host_alias}, and
15738 @samp{target_alias} are always exactly the arguments of @option{--build},
15739 @option{--host}, and @option{--target}; in particular, they are left empty
15740 if the user did not use them, even if the corresponding
15741 @code{AC_CANONICAL} macro was run. Any configure script may use these
15742 variables anywhere. These are the variables that should be used when in
15743 interaction with the user.
15745 If you need to recognize some special environments based on their system
15746 type, run the following macros to get canonical system names. These
15747 variables are not set before the macro call.
15749 If you use these macros, you must distribute @command{config.guess} and
15750 @command{config.sub} along with your source code. @xref{Output}, for
15751 information about the @code{AC_CONFIG_AUX_DIR} macro which you can use
15752 to control in which directory @command{configure} looks for those scripts.
15755 @defmac AC_CANONICAL_BUILD
15756 @acindex{CANONICAL_BUILD}
15759 @ovindex build_vendor
15761 Compute the canonical build-system type variable, @code{build}, and its
15762 three individual parts @code{build_cpu}, @code{build_vendor}, and
15765 If @option{--build} was specified, then @code{build} is the
15766 canonicalization of @code{build_alias} by @command{config.sub},
15767 otherwise it is determined by the shell script @command{config.guess}.
15770 @defmac AC_CANONICAL_HOST
15771 @acindex{CANONICAL_HOST}
15774 @ovindex host_vendor
15776 Compute the canonical host-system type variable, @code{host}, and its
15777 three individual parts @code{host_cpu}, @code{host_vendor}, and
15780 If @option{--host} was specified, then @code{host} is the
15781 canonicalization of @code{host_alias} by @command{config.sub},
15782 otherwise it defaults to @code{build}.
15785 @defmac AC_CANONICAL_TARGET
15786 @acindex{CANONICAL_TARGET}
15788 @ovindex target_cpu
15789 @ovindex target_vendor
15791 Compute the canonical target-system type variable, @code{target}, and its
15792 three individual parts @code{target_cpu}, @code{target_vendor}, and
15795 If @option{--target} was specified, then @code{target} is the
15796 canonicalization of @code{target_alias} by @command{config.sub},
15797 otherwise it defaults to @code{host}.
15800 Note that there can be artifacts due to the backward compatibility
15801 code. See @xref{Hosts and Cross-Compilation}, for more.
15803 @node Using System Type
15804 @section Using the System Type
15806 In @file{configure.ac} the system type is generally used by one or more
15807 @code{case} statements to select system-specifics. Shell wildcards can
15808 be used to match a group of system types.
15810 For example, an extra assembler code object file could be chosen, giving
15811 access to a CPU cycle counter register. @code{$(CYCLE_OBJ)} in the
15812 following would be used in a makefile to add the object to a
15813 program or library.
15817 alpha*-*-*) CYCLE_OBJ=rpcc.o ;;
15818 i?86-*-*) CYCLE_OBJ=rdtsc.o ;;
15821 AC_SUBST([CYCLE_OBJ])
15824 @code{AC_CONFIG_LINKS} (@pxref{Configuration Links}) is another good way
15825 to select variant source files, for example optimized code for some
15826 CPUs. The configured CPU type doesn't always indicate exact CPU types,
15827 so some runtime capability checks may be necessary too.
15831 alpha*-*-*) AC_CONFIG_LINKS([dither.c:alpha/dither.c]) ;;
15832 powerpc*-*-*) AC_CONFIG_LINKS([dither.c:powerpc/dither.c]) ;;
15833 *-*-*) AC_CONFIG_LINKS([dither.c:generic/dither.c]) ;;
15837 The host system type can also be used to find cross-compilation tools
15838 with @code{AC_CHECK_TOOL} (@pxref{Generic Programs}).
15840 The above examples all show @samp{$host}, since this is where the code
15841 is going to run. Only rarely is it necessary to test @samp{$build}
15842 (which is where the build is being done).
15844 Whenever you're tempted to use @samp{$host} it's worth considering
15845 whether some sort of probe would be better. New system types come along
15846 periodically or previously missing features are added. Well-written
15847 probes can adapt themselves to such things, but hard-coded lists of
15848 names can't. Here are some guidelines,
15852 Availability of libraries and library functions should always be checked
15855 Variant behavior of system calls is best identified with runtime tests
15856 if possible, but bug workarounds or obscure difficulties might have to
15857 be driven from @samp{$host}.
15859 Assembler code is inevitably highly CPU-specific and is best selected
15860 according to @samp{$host_cpu}.
15862 Assembler variations like underscore prefix on globals or ELF versus
15863 COFF type directives are however best determined by probing, perhaps
15864 even examining the compiler output.
15867 @samp{$target} is for use by a package creating a compiler or similar.
15868 For ordinary packages it's meaningless and should not be used. It
15869 indicates what the created compiler should generate code for, if it can
15870 cross-compile. @samp{$target} generally selects various hard-coded CPU
15871 and system conventions, since usually the compiler or tools under
15872 construction themselves determine how the target works.
15875 @c ===================================================== Site Configuration.
15877 @node Site Configuration
15878 @chapter Site Configuration
15880 @command{configure} scripts support several kinds of local configuration
15881 decisions. There are ways for users to specify where external software
15882 packages are, include or exclude optional features, install programs
15883 under modified names, and set default values for @command{configure}
15887 * Help Formatting:: Customizing @samp{configure --help}
15888 * External Software:: Working with other optional software
15889 * Package Options:: Selecting optional features
15890 * Pretty Help Strings:: Formatting help string
15891 * Option Checking:: Controlling checking of @command{configure} options
15892 * Site Details:: Configuring site details
15893 * Transforming Names:: Changing program names when installing
15894 * Site Defaults:: Giving @command{configure} local defaults
15897 @node Help Formatting
15898 @section Controlling Help Output
15900 Users consult @samp{configure --help} to learn of configuration
15901 decisions specific to your package. By default, @command{configure}
15902 breaks this output into sections for each type of option; within each
15903 section, help strings appear in the order @file{configure.ac} defines
15909 --enable-bar include bar
15916 @defmac AC_PRESERVE_HELP_ORDER
15917 @acindex{PRESERVE_HELP_ORDER}
15919 Request an alternate @option{--help} format, in which options of all
15920 types appear together, in the order defined. Call this macro before any
15921 @code{AC_ARG_ENABLE} or @code{AC_ARG_WITH}.
15924 Optional Features and Packages:
15926 --enable-bar include bar
15932 @node External Software
15933 @section Working With External Software
15934 @cindex External software
15936 Some packages require, or can optionally use, other software packages
15937 that are already installed. The user can give @command{configure}
15938 command line options to specify which such external software to use.
15939 The options have one of these forms:
15941 @c FIXME: Can't use @ovar here, Texinfo 4.0 goes lunatic and emits something
15944 --with-@var{package}[=@var{arg}]
15945 --without-@var{package}
15948 For example, @option{--with-gnu-ld} means work with the @acronym{GNU} linker
15949 instead of some other linker. @option{--with-x} means work with The X
15952 The user can give an argument by following the package name with
15953 @samp{=} and the argument. Giving an argument of @samp{no} is for
15954 packages that are used by default; it says to @emph{not} use the
15955 package. An argument that is neither @samp{yes} nor @samp{no} could
15956 include a name or number of a version of the other package, to specify
15957 more precisely which other package this program is supposed to work
15958 with. If no argument is given, it defaults to @samp{yes}.
15959 @option{--without-@var{package}} is equivalent to
15960 @option{--with-@var{package}=no}.
15962 Normally @command{configure} scripts complain about
15963 @option{--with-@var{package}} options that they do not support.
15964 @xref{Option Checking}, for details, and for how to override the
15967 For each external software package that may be used, @file{configure.ac}
15968 should call @code{AC_ARG_WITH} to detect whether the @command{configure}
15969 user asked to use it. Whether each package is used or not by default,
15970 and which arguments are valid, is up to you.
15972 @defmac AC_ARG_WITH (@var{package}, @var{help-string}, @ovar{action-if-given}, @ovar{action-if-not-given})
15974 If the user gave @command{configure} the option @option{--with-@var{package}}
15975 or @option{--without-@var{package}}, run shell commands
15976 @var{action-if-given}. If neither option was given, run shell commands
15977 @var{action-if-not-given}. The name @var{package} indicates another
15978 software package that this program should work with. It should consist
15979 only of alphanumeric characters, dashes, and dots.
15981 The option's argument is available to the shell commands
15982 @var{action-if-given} in the shell variable @code{withval}, which is
15983 actually just the value of the shell variable named
15984 @code{with_@var{package}}, with any non-alphanumeric characters in
15985 @var{package} changed into @samp{_}. You may use that variable instead,
15988 The argument @var{help-string} is a description of the option that
15991 --with-readline support fancy command line editing
15995 @var{help-string} may be more than one line long, if more detail is
15996 needed. Just make sure the columns line up in @samp{configure
15997 --help}. Avoid tabs in the help string. You'll need to enclose the
15998 help string in @samp{[} and @samp{]} in order to produce the leading
16001 You should format your @var{help-string} with the macro
16002 @code{AS_HELP_STRING} (@pxref{Pretty Help Strings}).
16004 The following example shows how to use the @code{AC_ARG_WITH} macro in
16005 a common situation. You want to let the user decide whether to enable
16006 support for an external library (e.g., the readline library); if the user
16007 specified neither @option{--with-readline} nor @option{--without-readline},
16008 you want to enable support for readline only if the library is available
16011 @c FIXME: Remove AS_IF when the problem of AC_REQUIRE within `if' is solved.
16013 AC_ARG_WITH([readline],
16014 [AS_HELP_STRING([--with-readline],
16015 [support fancy command line editing @@<:@@default=check@@:>@@])],
16017 [with_readline=check])
16020 AS_IF([test "x$with_readline" != xno],
16021 [AC_CHECK_LIB([readline], [main],
16022 [AC_SUBST([LIBREADLINE], ["-lreadline -lncurses"])
16023 AC_DEFINE([HAVE_LIBREADLINE], [1],
16024 [Define if you have libreadline])
16026 [if test "x$with_readline" != xcheck; then
16028 [--with-readline was given, but test for readline failed])
16033 The next example shows how to use @code{AC_ARG_WITH} to give the user the
16034 possibility to enable support for the readline library, in case it is still
16035 experimental and not well tested, and is therefore disabled by default.
16037 @c FIXME: Remove AS_IF when the problem of AC_REQUIRE within `if' is solved.
16039 AC_ARG_WITH([readline],
16040 [AS_HELP_STRING([--with-readline],
16041 [enable experimental support for readline])],
16043 [with_readline=no])
16046 AS_IF([test "x$with_readline" != xno],
16047 [AC_CHECK_LIB([readline], [main],
16048 [AC_SUBST([LIBREADLINE], ["-lreadline -lncurses"])
16049 AC_DEFINE([HAVE_LIBREADLINE], [1],
16050 [Define if you have libreadline])
16053 [--with-readline was given, but test for readline failed])],
16057 The last example shows how to use @code{AC_ARG_WITH} to give the user the
16058 possibility to disable support for the readline library, given that it is
16059 an important feature and that it should be enabled by default.
16061 @c FIXME: Remove AS_IF when the problem of AC_REQUIRE within `if' is solved.
16063 AC_ARG_WITH([readline],
16064 [AS_HELP_STRING([--without-readline],
16065 [disable support for readline])],
16067 [with_readline=yes])
16070 AS_IF([test "x$with_readline" != xno],
16071 [AC_CHECK_LIB([readline], [main],
16072 [AC_SUBST([LIBREADLINE], ["-lreadline -lncurses"])
16073 AC_DEFINE([HAVE_LIBREADLINE], [1],
16074 [Define if you have libreadline])
16077 [readline test failed (--without-readline to disable)])],
16081 These three examples can be easily adapted to the case where
16082 @code{AC_ARG_ENABLE} should be preferred to @code{AC_ARG_WITH} (see
16083 @ref{Package Options}).
16086 @defmac AC_WITH (@var{package}, @var{action-if-given}, @ovar{action-if-not-given})
16088 This is an obsolete version of @code{AC_ARG_WITH} that does not
16089 support providing a help string.
16092 @node Package Options
16093 @section Choosing Package Options
16094 @cindex Package options
16095 @cindex Options, package
16097 If a software package has optional compile-time features, the user can
16098 give @command{configure} command line options to specify whether to
16099 compile them. The options have one of these forms:
16101 @c FIXME: Can't use @ovar here, Texinfo 4.0 goes lunatic and emits something
16104 --enable-@var{feature}[=@var{arg}]
16105 --disable-@var{feature}
16108 These options allow users to choose which optional features to build and
16109 install. @option{--enable-@var{feature}} options should never make a
16110 feature behave differently or cause one feature to replace another.
16111 They should only cause parts of the program to be built rather than left
16114 The user can give an argument by following the feature name with
16115 @samp{=} and the argument. Giving an argument of @samp{no} requests
16116 that the feature @emph{not} be made available. A feature with an
16117 argument looks like @option{--enable-debug=stabs}. If no argument is
16118 given, it defaults to @samp{yes}. @option{--disable-@var{feature}} is
16119 equivalent to @option{--enable-@var{feature}=no}.
16121 Normally @command{configure} scripts complain about
16122 @option{--enable-@var{package}} options that they do not support.
16123 @xref{Option Checking}, for details, and for how to override the
16126 For each optional feature, @file{configure.ac} should call
16127 @code{AC_ARG_ENABLE} to detect whether the @command{configure} user asked
16128 to include it. Whether each feature is included or not by default, and
16129 which arguments are valid, is up to you.
16131 @defmac AC_ARG_ENABLE (@var{feature}, @var{help-string}, @ovar{action-if-given}, @ovar{action-if-not-given})
16132 @acindex{ARG_ENABLE}
16133 If the user gave @command{configure} the option
16134 @option{--enable-@var{feature}} or @option{--disable-@var{feature}}, run
16135 shell commands @var{action-if-given}. If neither option was given, run
16136 shell commands @var{action-if-not-given}. The name @var{feature}
16137 indicates an optional user-level facility. It should consist only of
16138 alphanumeric characters, dashes, and dots.
16140 The option's argument is available to the shell commands
16141 @var{action-if-given} in the shell variable @code{enableval}, which is
16142 actually just the value of the shell variable named
16143 @code{enable_@var{feature}}, with any non-alphanumeric characters in
16144 @var{feature} changed into @samp{_}. You may use that variable instead,
16145 if you wish. The @var{help-string} argument is like that of
16146 @code{AC_ARG_WITH} (@pxref{External Software}).
16148 You should format your @var{help-string} with the macro
16149 @code{AS_HELP_STRING} (@pxref{Pretty Help Strings}).
16151 See the examples suggested with the definition of @code{AC_ARG_WITH}
16152 (@pxref{External Software}) to get an idea of possible applications of
16153 @code{AC_ARG_ENABLE}.
16156 @defmac AC_ENABLE (@var{feature}, @var{action-if-given}, @ovar{action-if-not-given})
16158 This is an obsolete version of @code{AC_ARG_ENABLE} that does not
16159 support providing a help string.
16163 @node Pretty Help Strings
16164 @section Making Your Help Strings Look Pretty
16165 @cindex Help strings
16167 Properly formatting the @samp{help strings} which are used in
16168 @code{AC_ARG_WITH} (@pxref{External Software}) and @code{AC_ARG_ENABLE}
16169 (@pxref{Package Options}) can be challenging. Specifically, you want
16170 your own @samp{help strings} to line up in the appropriate columns of
16171 @samp{configure --help} just like the standard Autoconf @samp{help
16172 strings} do. This is the purpose of the @code{AS_HELP_STRING} macro.
16174 @defmac AS_HELP_STRING (@var{left-hand-side}, @var{right-hand-side})
16175 @acindex{HELP_STRING}
16177 Expands into an help string that looks pretty when the user executes
16178 @samp{configure --help}. It is typically used in @code{AC_ARG_WITH}
16179 (@pxref{External Software}) or @code{AC_ARG_ENABLE} (@pxref{Package
16180 Options}). The following example makes this clearer.
16184 [AS_HELP_STRING([--with-foo],
16185 [use foo (default is no)])],
16186 [use_foo=$withval],
16190 The second argument of @code{AS_HELP_STRING} is
16191 not a literal, and should not be double quoted.
16192 @xref{Autoconf Language}, for a more detailed explanation.
16193 Then the last few lines of @samp{configure --help} appear like
16197 --enable and --with options recognized:
16198 --with-foo use foo (default is no)
16201 The @code{AS_HELP_STRING} macro is particularly helpful when the
16202 @var{left-hand-side} and/or @var{right-hand-side} are composed of macro
16203 arguments, as shown in the following example.
16206 AC_DEFUN([MY_ARG_WITH],
16208 [AS_HELP_STRING([--with-$1], [use $1 (default is $2)])],
16209 [use_[]$1=$withval],
16215 @node Option Checking
16216 @section Controlling Checking of @command{configure} Options
16217 @cindex Options, Package
16219 The @command{configure} script checks its command-line options against a
16220 list of known options, like @option{--help} or @option{--config-cache}.
16221 An unknown option ordinarily indicates a mistake by the user and
16222 @command{configure} halts with an error. However, by default unknown
16223 @option{--with-@var{package}} and @option{--enable-@var{feature}}
16224 options elicit only a warning, to support configuring entire source
16227 Source trees often contain multiple packages with a top-level
16228 @command{configure} script that uses the @code{AC_CONFIG_SUBDIRS} macro
16229 (@pxref{Subdirectories}). Because the packages generally support
16230 different @option{--with-@var{package}} and
16231 @option{--enable-@var{feature}} options, the @acronym{GNU} Coding
16232 Standards say they must accept unrecognized options without halting.
16233 Even a warning message is undesirable here, so @code{AC_CONFIG_SUBDIRS}
16234 automatically disables the warnings.
16236 This default behavior may be modified in two ways. First, the installer
16237 can invoke @command{configure} with the
16238 @option{--disable-option-checking} or
16239 @option{--enable-option-checking=fatal} options to disable these
16240 warnings or turn them into fatal errors, respectively. Second, the
16241 maintainer can use @code{AC_DISABLE_OPTION_CHECKING}.
16243 @defmac AC_DISABLE_OPTION_CHECKING
16244 @acindex{DISABLE_OPTION_CHECKING}
16246 By default, disable warnings for unrecognized
16247 @option{--with-@var{package}} or @option{--enable-@var{feature}}
16248 options. This is implied by @code{AC_CONFIG_SUBDIRS}.
16250 The installer can override this behavior by passing
16251 @option{--enable-option-checking} (enable warnings) or
16252 @option{--enable-option-checking=fatal} (enable errors) to
16253 @command{configure}.
16258 @section Configuring Site Details
16259 @cindex Site details
16261 Some software packages require complex site-specific information. Some
16262 examples are host names to use for certain services, company names, and
16263 email addresses to contact. Since some configuration scripts generated
16264 by Metaconfig ask for such information interactively, people sometimes
16265 wonder how to get that information in Autoconf-generated configuration
16266 scripts, which aren't interactive.
16268 Such site configuration information should be put in a file that is
16269 edited @emph{only by users}, not by programs. The location of the file
16270 can either be based on the @code{prefix} variable, or be a standard
16271 location such as the user's home directory. It could even be specified
16272 by an environment variable. The programs should examine that file at
16273 runtime, rather than at compile time. Runtime configuration is more
16274 convenient for users and makes the configuration process simpler than
16275 getting the information while configuring. @xref{Directory Variables, ,
16276 Variables for Installation Directories, standards, @acronym{GNU} Coding
16277 Standards}, for more information on where to put data files.
16279 @node Transforming Names
16280 @section Transforming Program Names When Installing
16281 @cindex Transforming program names
16282 @cindex Program names, transforming
16284 Autoconf supports changing the names of programs when installing them.
16285 In order to use these transformations, @file{configure.ac} must call the
16286 macro @code{AC_ARG_PROGRAM}.
16288 @defmac AC_ARG_PROGRAM
16289 @acindex{ARG_PROGRAM}
16290 @ovindex program_transform_name
16291 Place in output variable @code{program_transform_name} a sequence of
16292 @code{sed} commands for changing the names of installed programs.
16294 If any of the options described below are given to @command{configure},
16295 program names are transformed accordingly. Otherwise, if
16296 @code{AC_CANONICAL_TARGET} has been called and a @option{--target} value
16297 is given, the target type followed by a dash is used as a prefix.
16298 Otherwise, no program name transformation is done.
16302 * Transformation Options:: @command{configure} options to transform names
16303 * Transformation Examples:: Sample uses of transforming names
16304 * Transformation Rules:: Makefile uses of transforming names
16307 @node Transformation Options
16308 @subsection Transformation Options
16310 You can specify name transformations by giving @command{configure} these
16311 command line options:
16314 @item --program-prefix=@var{prefix}
16315 prepend @var{prefix} to the names;
16317 @item --program-suffix=@var{suffix}
16318 append @var{suffix} to the names;
16320 @item --program-transform-name=@var{expression}
16321 perform @code{sed} substitution @var{expression} on the names.
16324 @node Transformation Examples
16325 @subsection Transformation Examples
16327 These transformations are useful with programs that can be part of a
16328 cross-compilation development environment. For example, a
16329 cross-assembler running on a Sun 4 configured with
16330 @option{--target=i960-vxworks} is normally installed as
16331 @file{i960-vxworks-as}, rather than @file{as}, which could be confused
16332 with a native Sun 4 assembler.
16334 You can force a program name to begin with @file{g}, if you don't want
16335 @acronym{GNU} programs installed on your system to shadow other programs with
16336 the same name. For example, if you configure @acronym{GNU} @code{diff} with
16337 @option{--program-prefix=g}, then when you run @samp{make install} it is
16338 installed as @file{/usr/local/bin/gdiff}.
16340 As a more sophisticated example, you could use
16343 --program-transform-name='s/^/g/; s/^gg/g/; s/^gless/less/'
16347 to prepend @samp{g} to most of the program names in a source tree,
16348 excepting those like @code{gdb} that already have one and those like
16349 @code{less} and @code{lesskey} that aren't @acronym{GNU} programs. (That is
16350 assuming that you have a source tree containing those programs that is
16351 set up to use this feature.)
16353 One way to install multiple versions of some programs simultaneously is
16354 to append a version number to the name of one or both. For example, if
16355 you want to keep Autoconf version 1 around for awhile, you can configure
16356 Autoconf version 2 using @option{--program-suffix=2} to install the
16357 programs as @file{/usr/local/bin/autoconf2},
16358 @file{/usr/local/bin/autoheader2}, etc. Nevertheless, pay attention
16359 that only the binaries are renamed, therefore you'd have problems with
16360 the library files which might overlap.
16362 @node Transformation Rules
16363 @subsection Transformation Rules
16365 Here is how to use the variable @code{program_transform_name} in a
16366 @file{Makefile.in}:
16369 PROGRAMS = cp ls rm
16370 transform = @@program_transform_name@@
16372 for p in $(PROGRAMS); do \
16373 $(INSTALL_PROGRAM) $$p $(DESTDIR)$(bindir)/`echo $$p | \
16374 sed '$(transform)'`; \
16378 for p in $(PROGRAMS); do \
16379 rm -f $(DESTDIR)$(bindir)/`echo $$p | sed '$(transform)'`; \
16383 It is guaranteed that @code{program_transform_name} is never empty, and
16384 that there are no useless separators. Therefore you may safely embed
16385 @code{program_transform_name} within a sed program using @samp{;}:
16388 transform = @@program_transform_name@@
16389 transform_exe = s/$(EXEEXT)$$//;$(transform);s/$$/$(EXEEXT)/
16392 Whether to do the transformations on documentation files (Texinfo or
16393 @code{man}) is a tricky question; there seems to be no perfect answer,
16394 due to the several reasons for name transforming. Documentation is not
16395 usually particular to a specific architecture, and Texinfo files do not
16396 conflict with system documentation. But they might conflict with
16397 earlier versions of the same files, and @code{man} pages sometimes do
16398 conflict with system documentation. As a compromise, it is probably
16399 best to do name transformations on @code{man} pages but not on Texinfo
16402 @node Site Defaults
16403 @section Setting Site Defaults
16404 @cindex Site defaults
16406 Autoconf-generated @command{configure} scripts allow your site to provide
16407 default values for some configuration values. You do this by creating
16408 site- and system-wide initialization files.
16410 @evindex CONFIG_SITE
16411 If the environment variable @code{CONFIG_SITE} is set, @command{configure}
16412 uses its value as the name of a shell script to read. Otherwise, it
16413 reads the shell script @file{@var{prefix}/share/config.site} if it exists,
16414 then @file{@var{prefix}/etc/config.site} if it exists. Thus,
16415 settings in machine-specific files override those in machine-independent
16416 ones in case of conflict.
16418 Site files can be arbitrary shell scripts, but only certain kinds of
16419 code are really appropriate to be in them. Because @command{configure}
16420 reads any cache file after it has read any site files, a site file can
16421 define a default cache file to be shared between all Autoconf-generated
16422 @command{configure} scripts run on that system (@pxref{Cache Files}). If
16423 you set a default cache file in a site file, it is a good idea to also
16424 set the output variable @code{CC} in that site file, because the cache
16425 file is only valid for a particular compiler, but many systems have
16428 You can examine or override the value set by a command line option to
16429 @command{configure} in a site file; options set shell variables that have
16430 the same names as the options, with any dashes turned into underscores.
16431 The exceptions are that @option{--without-} and @option{--disable-} options
16432 are like giving the corresponding @option{--with-} or @option{--enable-}
16433 option and the value @samp{no}. Thus, @option{--cache-file=localcache}
16434 sets the variable @code{cache_file} to the value @samp{localcache};
16435 @option{--enable-warnings=no} or @option{--disable-warnings} sets the variable
16436 @code{enable_warnings} to the value @samp{no}; @option{--prefix=/usr} sets the
16437 variable @code{prefix} to the value @samp{/usr}; etc.
16439 Site files are also good places to set default values for other output
16440 variables, such as @code{CFLAGS}, if you need to give them non-default
16441 values: anything you would normally do, repetitively, on the command
16442 line. If you use non-default values for @var{prefix} or
16443 @var{exec_prefix} (wherever you locate the site file), you can set them
16444 in the site file if you specify it with the @code{CONFIG_SITE}
16445 environment variable.
16447 You can set some cache values in the site file itself. Doing this is
16448 useful if you are cross-compiling, where it is impossible to check features
16449 that require running a test program. You could ``prime the cache'' by
16450 setting those values correctly for that system in
16451 @file{@var{prefix}/etc/config.site}. To find out the names of the cache
16452 variables you need to set, look for shell variables with @samp{_cv_} in
16453 their names in the affected @command{configure} scripts, or in the Autoconf
16454 M4 source code for those macros.
16456 The cache file is careful to not override any variables set in the site
16457 files. Similarly, you should not override command-line options in the
16458 site files. Your code should check that variables such as @code{prefix}
16459 and @code{cache_file} have their default values (as set near the top of
16460 @command{configure}) before changing them.
16462 Here is a sample file @file{/usr/share/local/gnu/share/config.site}. The
16463 command @samp{configure --prefix=/usr/share/local/gnu} would read this
16464 file (if @code{CONFIG_SITE} is not set to a different file).
16467 # config.site for configure
16469 # Change some defaults.
16470 test "$prefix" = NONE && prefix=/usr/share/local/gnu
16471 test "$exec_prefix" = NONE && exec_prefix=/usr/local/gnu
16472 test "$sharedstatedir" = '$prefix/com' && sharedstatedir=/var
16473 test "$localstatedir" = '$prefix/var' && localstatedir=/var
16475 # Give Autoconf 2.x generated configure scripts a shared default
16476 # cache file for feature test results, architecture-specific.
16477 if test "$cache_file" = /dev/null; then
16478 cache_file="$prefix/var/config.cache"
16479 # A cache file is only valid for one C compiler.
16485 @c ============================================== Running configure Scripts.
16487 @node Running configure Scripts
16488 @chapter Running @command{configure} Scripts
16489 @cindex @command{configure}
16491 Below are instructions on how to configure a package that uses a
16492 @command{configure} script, suitable for inclusion as an @file{INSTALL}
16493 file in the package. A plain-text version of @file{INSTALL} which you
16494 may use comes with Autoconf.
16497 * Basic Installation:: Instructions for typical cases
16498 * Compilers and Options:: Selecting compilers and optimization
16499 * Multiple Architectures:: Compiling for multiple architectures at once
16500 * Installation Names:: Installing in different directories
16501 * Optional Features:: Selecting optional features
16502 * System Type:: Specifying the system type
16503 * Sharing Defaults:: Setting site-wide defaults for @command{configure}
16504 * Defining Variables:: Specifying the compiler etc.
16505 * configure Invocation:: Changing how @command{configure} runs
16509 @include install.texi
16512 @c ============================================== config.status Invocation
16514 @node config.status Invocation
16515 @chapter config.status Invocation
16516 @cindex @command{config.status}
16518 The @command{configure} script creates a file named @file{config.status},
16519 which actually configures, @dfn{instantiates}, the template files. It
16520 also records the configuration options that were specified when the
16521 package was last configured in case reconfiguring is needed.
16525 ./config.status @var{option}@dots{} [@var{file}@dots{}]
16528 It configures the @var{files}; if none are specified, all the templates
16529 are instantiated. The files must be specified without their
16530 dependencies, as in
16533 ./config.status foobar
16540 ./config.status foobar:foo.in:bar.in
16543 The supported options are:
16548 Print a summary of the command line options, the list of the template
16553 Print the version number of Autoconf and the configuration settings,
16559 Do not print progress messages.
16563 Don't remove the temporary files.
16565 @item --file=@var{file}[:@var{template}]
16566 Require that @var{file} be instantiated as if
16567 @samp{AC_CONFIG_FILES(@var{file}:@var{template})} was used. Both
16568 @var{file} and @var{template} may be @samp{-} in which case the standard
16569 output and/or standard input, respectively, is used. If a
16570 @var{template} file name is relative, it is first looked for in the build
16571 tree, and then in the source tree. @xref{Configuration Actions}, for
16574 This option and the following ones provide one way for separately
16575 distributed packages to share the values computed by @command{configure}.
16576 Doing so can be useful if some of the packages need a superset of the
16577 features that one of them, perhaps a common library, does. These
16578 options allow a @file{config.status} file to create files other than the
16579 ones that its @file{configure.ac} specifies, so it can be used for a
16582 @item --header=@var{file}[:@var{template}]
16583 Same as @option{--file} above, but with @samp{AC_CONFIG_HEADERS}.
16586 Ask @file{config.status} to update itself and exit (no instantiation).
16587 This option is useful if you change @command{configure}, so that the
16588 results of some tests might be different from the previous run. The
16589 @option{--recheck} option reruns @command{configure} with the same arguments
16590 you used before, plus the @option{--no-create} option, which prevents
16591 @command{configure} from running @file{config.status} and creating
16592 @file{Makefile} and other files, and the @option{--no-recursion} option,
16593 which prevents @command{configure} from running other @command{configure}
16594 scripts in subdirectories. (This is so other Make rules can
16595 run @file{config.status} when it changes; @pxref{Automatic Remaking},
16599 @file{config.status} checks several optional environment variables that
16600 can alter its behavior:
16602 @defvar CONFIG_SHELL
16603 @evindex CONFIG_SHELL
16604 The shell with which to run @command{configure} for the @option{--recheck}
16605 option. It must be Bourne-compatible. The default is a shell that
16606 supports @code{LINENO} if available, and @file{/bin/sh} otherwise.
16607 Invoking @command{configure} by hand bypasses this setting, so you may
16608 need to use a command like @samp{CONFIG_SHELL=/bin/bash /bin/bash ./configure}
16609 to insure that the same shell is used everywhere. The absolute name of the
16610 shell should be passed.
16613 @defvar CONFIG_STATUS
16614 @evindex CONFIG_STATUS
16615 The file name to use for the shell script that records the
16616 configuration. The default is @file{./config.status}. This variable is
16617 useful when one package uses parts of another and the @command{configure}
16618 scripts shouldn't be merged because they are maintained separately.
16621 You can use @file{./config.status} in your makefiles. For example, in
16622 the dependencies given above (@pxref{Automatic Remaking}),
16623 @file{config.status} is run twice when @file{configure.ac} has changed.
16624 If that bothers you, you can make each run only regenerate the files for
16629 stamp-h: config.h.in config.status
16630 ./config.status config.h
16633 Makefile: Makefile.in config.status
16634 ./config.status Makefile
16638 The calling convention of @file{config.status} has changed; see
16639 @ref{Obsolete config.status Use}, for details.
16642 @c =================================================== Obsolete Constructs
16644 @node Obsolete Constructs
16645 @chapter Obsolete Constructs
16646 @cindex Obsolete constructs
16648 Autoconf changes, and throughout the years some constructs have been
16649 obsoleted. Most of the changes involve the macros, but in some cases
16650 the tools themselves, or even some concepts, are now considered
16653 You may completely skip this chapter if you are new to Autoconf. Its
16654 intention is mainly to help maintainers updating their packages by
16655 understanding how to move to more modern constructs.
16658 * Obsolete config.status Use:: Obsolete convention for @command{config.status}
16659 * acconfig Header:: Additional entries in @file{config.h.in}
16660 * autoupdate Invocation:: Automatic update of @file{configure.ac}
16661 * Obsolete Macros:: Backward compatibility macros
16662 * Autoconf 1:: Tips for upgrading your files
16663 * Autoconf 2.13:: Some fresher tips
16666 @node Obsolete config.status Use
16667 @section Obsolete @file{config.status} Invocation
16669 @file{config.status} now supports arguments to specify the files to
16670 instantiate; see @ref{config.status Invocation}, for more details.
16671 Before, environment variables had to be used.
16673 @defvar CONFIG_COMMANDS
16674 @evindex CONFIG_COMMANDS
16675 The tags of the commands to execute. The default is the arguments given
16676 to @code{AC_OUTPUT} and @code{AC_CONFIG_COMMANDS} in
16677 @file{configure.ac}.
16680 @defvar CONFIG_FILES
16681 @evindex CONFIG_FILES
16682 The files in which to perform @samp{@@@var{variable}@@} substitutions.
16683 The default is the arguments given to @code{AC_OUTPUT} and
16684 @code{AC_CONFIG_FILES} in @file{configure.ac}.
16687 @defvar CONFIG_HEADERS
16688 @evindex CONFIG_HEADERS
16689 The files in which to substitute C @code{#define} statements. The
16690 default is the arguments given to @code{AC_CONFIG_HEADERS}; if that
16691 macro was not called, @file{config.status} ignores this variable.
16694 @defvar CONFIG_LINKS
16695 @evindex CONFIG_LINKS
16696 The symbolic links to establish. The default is the arguments given to
16697 @code{AC_CONFIG_LINKS}; if that macro was not called,
16698 @file{config.status} ignores this variable.
16701 In @ref{config.status Invocation}, using this old interface, the example
16707 stamp-h: config.h.in config.status
16708 CONFIG_COMMANDS= CONFIG_LINKS= CONFIG_FILES= \
16709 CONFIG_HEADERS=config.h ./config.status
16712 Makefile: Makefile.in config.status
16713 CONFIG_COMMANDS= CONFIG_LINKS= CONFIG_HEADERS= \
16714 CONFIG_FILES=Makefile ./config.status
16719 (If @file{configure.ac} does not call @code{AC_CONFIG_HEADERS}, there is
16720 no need to set @code{CONFIG_HEADERS} in the @code{make} rules. Equally
16721 for @code{CONFIG_COMMANDS}, etc.)
16724 @node acconfig Header
16725 @section @file{acconfig.h}
16727 @cindex @file{acconfig.h}
16728 @cindex @file{config.h.top}
16729 @cindex @file{config.h.bot}
16731 In order to produce @file{config.h.in}, @command{autoheader} needs to
16732 build or to find templates for each symbol. Modern releases of Autoconf
16733 use @code{AH_VERBATIM} and @code{AH_TEMPLATE} (@pxref{Autoheader
16734 Macros}), but in older releases a file, @file{acconfig.h}, contained the
16735 list of needed templates. @command{autoheader} copied comments and
16736 @code{#define} and @code{#undef} statements from @file{acconfig.h} in
16737 the current directory, if present. This file used to be mandatory if
16738 you @code{AC_DEFINE} any additional symbols.
16740 Modern releases of Autoconf also provide @code{AH_TOP} and
16741 @code{AH_BOTTOM} if you need to prepend/append some information to
16742 @file{config.h.in}. Ancient versions of Autoconf had a similar feature:
16743 if @file{./acconfig.h} contains the string @samp{@@TOP@@},
16744 @command{autoheader} copies the lines before the line containing
16745 @samp{@@TOP@@} into the top of the file that it generates. Similarly,
16746 if @file{./acconfig.h} contains the string @samp{@@BOTTOM@@},
16747 @command{autoheader} copies the lines after that line to the end of the
16748 file it generates. Either or both of those strings may be omitted. An
16749 even older alternate way to produce the same effect in ancient versions
16750 of Autoconf is to create the files @file{@var{file}.top} (typically
16751 @file{config.h.top}) and/or @file{@var{file}.bot} in the current
16752 directory. If they exist, @command{autoheader} copies them to the
16753 beginning and end, respectively, of its output.
16755 In former versions of Autoconf, the files used in preparing a software
16756 package for distribution were:
16759 configure.ac --. .------> autoconf* -----> configure
16761 [aclocal.m4] --+ `---.
16763 +--> [autoheader*] -> [config.h.in]
16764 [acconfig.h] ----. |
16771 Using only the @code{AH_} macros, @file{configure.ac} should be
16772 self-contained, and should not depend upon @file{acconfig.h} etc.
16775 @node autoupdate Invocation
16776 @section Using @command{autoupdate} to Modernize @file{configure.ac}
16777 @cindex @command{autoupdate}
16779 The @command{autoupdate} program updates a @file{configure.ac} file that
16780 calls Autoconf macros by their old names to use the current macro names.
16781 In version 2 of Autoconf, most of the macros were renamed to use a more
16782 uniform and descriptive naming scheme. @xref{Macro Names}, for a
16783 description of the new scheme. Although the old names still work
16784 (@pxref{Obsolete Macros}, for a list of the old macros and the corresponding
16785 new names), you can make your @file{configure.ac} files more readable
16786 and make it easier to use the current Autoconf documentation if you
16787 update them to use the new macro names.
16789 @evindex SIMPLE_BACKUP_SUFFIX
16790 If given no arguments, @command{autoupdate} updates @file{configure.ac},
16791 backing up the original version with the suffix @file{~} (or the value
16792 of the environment variable @code{SIMPLE_BACKUP_SUFFIX}, if that is
16793 set). If you give @command{autoupdate} an argument, it reads that file
16794 instead of @file{configure.ac} and writes the updated file to the
16798 @command{autoupdate} accepts the following options:
16803 Print a summary of the command line options and exit.
16807 Print the version number of Autoconf and exit.
16811 Report processing steps.
16815 Don't remove the temporary files.
16819 Force the update even if the file has not changed. Disregard the cache.
16821 @item --include=@var{dir}
16822 @itemx -I @var{dir}
16823 Also look for input files in @var{dir}. Multiple invocations accumulate.
16824 Directories are browsed from last to first.
16827 @node Obsolete Macros
16828 @section Obsolete Macros
16830 Several macros are obsoleted in Autoconf, for various reasons (typically
16831 they failed to quote properly, couldn't be extended for more recent
16832 issues, etc.). They are still supported, but deprecated: their use
16835 During the jump from Autoconf version 1 to version 2, most of the
16836 macros were renamed to use a more uniform and descriptive naming scheme,
16837 but their signature did not change. @xref{Macro Names}, for a
16838 description of the new naming scheme. Below, if there is just the mapping
16839 from old names to new names for these macros, the reader is invited to
16840 refer to the definition of the new macro for the signature and the
16845 @code{AC_FUNC_ALLOCA}
16848 @defmac AC_ARG_ARRAY
16849 @acindex{ARG_ARRAY}
16850 removed because of limited usefulness
16855 This macro is obsolete; it does nothing.
16858 @defmac AC_C_LONG_DOUBLE
16859 @acindex{C_LONG_DOUBLE}
16860 @cvindex HAVE_LONG_DOUBLE
16861 If the C compiler supports a working @code{long double} type with more
16862 range or precision than the @code{double} type, define
16863 @code{HAVE_LONG_DOUBLE}.
16865 You should use @code{AC_TYPE_LONG_DOUBLE} or
16866 @code{AC_TYPE_LONG_DOUBLE_WIDER} instead. @xref{Particular Types}.
16869 @defmac AC_CANONICAL_SYSTEM
16870 @acindex{CANONICAL_SYSTEM}
16871 Determine the system type and set output variables to the names of the
16872 canonical system types. @xref{Canonicalizing}, for details about the
16873 variables this macro sets.
16875 The user is encouraged to use either @code{AC_CANONICAL_BUILD}, or
16876 @code{AC_CANONICAL_HOST}, or @code{AC_CANONICAL_TARGET}, depending on
16877 the needs. Using @code{AC_CANONICAL_TARGET} is enough to run the two
16881 @defmac AC_CHAR_UNSIGNED
16882 @acindex{CHAR_UNSIGNED}
16883 @code{AC_C_CHAR_UNSIGNED}
16886 @defmac AC_CHECK_TYPE (@var{type}, @var{default})
16887 @acindex{CHECK_TYPE}
16888 Autoconf, up to 2.13, used to provide this version of
16889 @code{AC_CHECK_TYPE}, deprecated because of its flaws. First, although
16890 it is a member of the @code{CHECK} clan, it does
16891 more than just checking. Secondly, missing types are defined
16892 using @code{#define}, not @code{typedef}, and this can lead to
16893 problems in the case of pointer types.
16895 This use of @code{AC_CHECK_TYPE} is obsolete and discouraged; see
16896 @ref{Generic Types}, for the description of the current macro.
16898 If the type @var{type} is not defined, define it to be the C (or C++)
16899 builtin type @var{default}, e.g., @samp{short int} or @samp{unsigned int}.
16901 This macro is equivalent to:
16904 AC_CHECK_TYPE([@var{type}], [],
16905 [AC_DEFINE_UNQUOTED([@var{type}], [@var{default}],
16906 [Define to `@var{default}'
16907 if <sys/types.h> does not define.])])
16910 In order to keep backward compatibility, the two versions of
16911 @code{AC_CHECK_TYPE} are implemented, selected using these heuristics:
16915 If there are three or four arguments, the modern version is used.
16918 If the second argument appears to be a C or C++ type, then the
16919 obsolete version is used. This happens if the argument is a C or C++
16920 @emph{builtin} type or a C identifier ending in @samp{_t}, optionally
16921 followed by one of @samp{[(* } and then by a string of zero or more
16922 characters taken from the set @samp{[]()* _a-zA-Z0-9}.
16925 If the second argument is spelled with the alphabet of valid C and C++
16926 types, the user is warned and the modern version is used.
16929 Otherwise, the modern version is used.
16933 You are encouraged either to use a valid builtin type, or to use the
16934 equivalent modern code (see above), or better yet, to use
16935 @code{AC_CHECK_TYPES} together with
16938 #ifndef HAVE_LOFF_T
16939 typedef loff_t off_t;
16943 @c end of AC_CHECK_TYPE
16945 @defmac AC_CHECKING (@var{feature-description})
16947 Same as @samp{AC_MSG_NOTICE([checking @var{feature-description}@dots{}]}.
16950 @defmac AC_COMPILE_CHECK (@var{echo-text}, @var{includes}, @var{function-body}, @var{action-if-true}, @ovar{action-if-false})
16951 @acindex{COMPILE_CHECK}
16952 This is an obsolete version of @code{AC_TRY_COMPILE} itself replaced by
16953 @code{AC_COMPILE_IFELSE} (@pxref{Running the Compiler}), with the
16954 addition that it prints @samp{checking for @var{echo-text}} to the
16955 standard output first, if @var{echo-text} is non-empty. Use
16956 @code{AC_MSG_CHECKING} and @code{AC_MSG_RESULT} instead to print
16957 messages (@pxref{Printing Messages}).
16965 @defmac AC_CROSS_CHECK
16966 @acindex{CROSS_CHECK}
16967 Same as @code{AC_C_CROSS}, which is obsolete too, and does nothing
16973 Check for the Cygwin environment in which case the shell variable
16974 @code{CYGWIN} is set to @samp{yes}. Don't use this macro, the dignified
16975 means to check the nature of the host is using
16976 @code{AC_CANONICAL_HOST}. As a matter of fact this macro is defined as:
16979 AC_REQUIRE([AC_CANONICAL_HOST])[]dnl
16981 *cygwin* ) CYGWIN=yes;;
16986 Beware that the variable @code{CYGWIN} has a special meaning when
16987 running Cygwin, and should not be changed. That's yet another reason
16988 not to use this macro.
16991 @defmac AC_DECL_SYS_SIGLIST
16992 @acindex{DECL_SYS_SIGLIST}
16993 @cvindex SYS_SIGLIST_DECLARED
16997 AC_CHECK_DECLS([sys_siglist], [], [],
16998 [#include <signal.h>
16999 /* NetBSD declares sys_siglist in unistd.h. */
17000 #ifdef HAVE_UNISTD_H
17001 # include <unistd.h>
17007 @defmac AC_DECL_YYTEXT
17008 @acindex{DECL_YYTEXT}
17009 Does nothing, now integrated in @code{AC_PROG_LEX}.
17012 @defmac AC_DIR_HEADER
17013 @acindex{DIR_HEADER}
17018 Like calling @code{AC_FUNC_CLOSEDIR_VOID} and@code{AC_HEADER_DIRENT},
17019 but defines a different set of C preprocessor macros to indicate which
17020 header file is found:
17022 @multitable {@file{sys/ndir.h}} {Old Symbol} {@code{HAVE_SYS_NDIR_H}}
17023 @item Header @tab Old Symbol @tab New Symbol
17024 @item @file{dirent.h} @tab @code{DIRENT} @tab @code{HAVE_DIRENT_H}
17025 @item @file{sys/ndir.h} @tab @code{SYSNDIR} @tab @code{HAVE_SYS_NDIR_H}
17026 @item @file{sys/dir.h} @tab @code{SYSDIR} @tab @code{HAVE_SYS_DIR_H}
17027 @item @file{ndir.h} @tab @code{NDIR} @tab @code{HAVE_NDIR_H}
17031 @defmac AC_DYNIX_SEQ
17032 @acindex{DYNIX_SEQ}
17033 If on DYNIX/ptx, add @option{-lseq} to output variable
17034 @code{LIBS}. This macro used to be defined as
17037 AC_CHECK_LIB([seq], [getmntent], [LIBS="-lseq $LIBS"])
17041 now it is just @code{AC_FUNC_GETMNTENT}.
17047 Defined the output variable @code{EXEEXT} based on the output of the
17048 compiler, which is now done automatically. Typically set to empty
17049 string if Posix and @samp{.exe} if a @acronym{DOS} variant.
17054 Similar to @code{AC_CYGWIN} but checks for the EMX environment on OS/2
17055 and sets @code{EMXOS2}.
17060 @code{AC_MSG_ERROR}
17068 @defmac AC_FIND_XTRA
17069 @acindex{FIND_XTRA}
17070 @code{AC_PATH_XTRA}
17075 @code{m4_foreach_w}
17078 @defmac AC_FUNC_CHECK
17079 @acindex{FUNC_CHECK}
17080 @code{AC_CHECK_FUNC}
17083 @defmac AC_FUNC_SETVBUF_REVERSED
17084 @acindex{FUNC_SETVBUF_REVERSED}
17085 @cvindex SETVBUF_REVERSED
17086 @c @fuindex setvbuf
17087 @prindex @code{setvbuf}
17088 Do nothing. Formerly, this macro checked whether @code{setvbuf} takes
17089 the buffering type as its second argument and the buffer pointer as the
17090 third, instead of the other way around, and defined
17091 @code{SETVBUF_REVERSED}. However, the last systems to have the problem
17092 were those based on SVR2, which became obsolete in 1987, and the macro
17093 is no longer needed.
17096 @defmac AC_FUNC_WAIT3
17097 @acindex{FUNC_WAIT3}
17098 @cvindex HAVE_WAIT3
17099 If @code{wait3} is found and fills in the contents of its third argument
17100 (a @samp{struct rusage *}), which @acronym{HP-UX} does not do, define
17103 These days portable programs should use @code{waitpid}, not
17104 @code{wait3}, as @code{wait3} has been removed from Posix.
17107 @defmac AC_GCC_TRADITIONAL
17108 @acindex{GCC_TRADITIONAL}
17109 @code{AC_PROG_GCC_TRADITIONAL}
17112 @defmac AC_GETGROUPS_T
17113 @acindex{GETGROUPS_T}
17114 @code{AC_TYPE_GETGROUPS}
17117 @defmac AC_GETLOADAVG
17118 @acindex{GETLOADAVG}
17119 @code{AC_FUNC_GETLOADAVG}
17122 @defmac AC_HAVE_FUNCS
17123 @acindex{HAVE_FUNCS}
17124 @code{AC_CHECK_FUNCS}
17127 @defmac AC_HAVE_HEADERS
17128 @acindex{HAVE_HEADERS}
17129 @code{AC_CHECK_HEADERS}
17132 @defmac AC_HAVE_LIBRARY (@var{library}, @ovar{action-if-found}, @ovar{action-if-not-found}, @ovar{other-libraries})
17133 @acindex{HAVE_LIBRARY}
17134 This macro is equivalent to calling @code{AC_CHECK_LIB} with a
17135 @var{function} argument of @code{main}. In addition, @var{library} can
17136 be written as any of @samp{foo}, @option{-lfoo}, or @samp{libfoo.a}. In
17137 all of those cases, the compiler is passed @option{-lfoo}. However,
17138 @var{library} cannot be a shell variable; it must be a literal name.
17141 @defmac AC_HAVE_POUNDBANG
17142 @acindex{HAVE_POUNDBANG}
17143 @code{AC_SYS_INTERPRETER} (different calling convention)
17146 @defmac AC_HEADER_CHECK
17147 @acindex{HEADER_CHECK}
17148 @code{AC_CHECK_HEADER}
17151 @defmac AC_HEADER_EGREP
17152 @acindex{HEADER_EGREP}
17153 @code{AC_EGREP_HEADER}
17156 @defmac AC_HELP_STRING
17157 @acindex{HELP_STRING}
17158 @code{AS_HELP_STRING}
17161 @defmac AC_INIT (@var{unique-file-in-source-dir})
17163 Formerly @code{AC_INIT} used to have a single argument, and was
17168 AC_CONFIG_SRCDIR(@var{unique-file-in-source-dir})
17177 @defmac AC_INT_16_BITS
17178 @acindex{INT_16_BITS}
17179 @cvindex INT_16_BITS
17180 If the C type @code{int} is 16 bits wide, define @code{INT_16_BITS}.
17181 Use @samp{AC_CHECK_SIZEOF(int)} instead.
17184 @defmac AC_IRIX_SUN
17186 If on @sc{irix} (Silicon Graphics Unix), add @option{-lsun} to output
17187 @code{LIBS}. If you were using it to get @code{getmntent}, use
17188 @code{AC_FUNC_GETMNTENT} instead. If you used it for the NIS versions
17189 of the password and group functions, use @samp{AC_CHECK_LIB(sun,
17190 getpwnam)}. Up to Autoconf 2.13, it used to be
17193 AC_CHECK_LIB([sun], [getmntent], [LIBS="-lsun $LIBS"])
17197 now it is defined as
17201 AC_CHECK_LIB([sun], [getpwnam])
17207 Same as @samp{AC_LANG([C])}.
17210 @defmac AC_LANG_CPLUSPLUS
17211 @acindex{LANG_CPLUSPLUS}
17212 Same as @samp{AC_LANG([C++])}.
17215 @defmac AC_LANG_FORTRAN77
17216 @acindex{LANG_FORTRAN77}
17217 Same as @samp{AC_LANG([Fortran 77])}.
17220 @defmac AC_LANG_RESTORE
17221 @acindex{LANG_RESTORE}
17222 Select the @var{language} that is saved on the top of the stack, as set
17223 by @code{AC_LANG_SAVE}, remove it from the stack, and call
17224 @code{AC_LANG(@var{language})}.
17227 @defmac AC_LANG_SAVE
17228 @acindex{LANG_SAVE}
17229 Remember the current language (as set by @code{AC_LANG}) on a stack.
17230 The current language does not change. @code{AC_LANG_PUSH} is preferred.
17233 @defmac AC_LINK_FILES (@var{source}@dots{}, @var{dest}@dots{})
17234 @acindex{LINK_FILES}
17235 This is an obsolete version of @code{AC_CONFIG_LINKS}. An updated
17239 AC_LINK_FILES(config/$machine.h config/$obj_format.h,
17247 AC_CONFIG_LINKS([host.h:config/$machine.h
17248 object.h:config/$obj_format.h])
17254 @code{AC_PROG_LN_S}
17257 @defmac AC_LONG_64_BITS
17258 @acindex{LONG_64_BITS}
17259 @cvindex LONG_64_BITS
17260 Define @code{LONG_64_BITS} if the C type @code{long int} is 64 bits wide.
17261 Use the generic macro @samp{AC_CHECK_SIZEOF([long int])} instead.
17264 @defmac AC_LONG_DOUBLE
17265 @acindex{LONG_DOUBLE}
17266 If the C compiler supports a working @code{long double} type with more
17267 range or precision than the @code{double} type, define
17268 @code{HAVE_LONG_DOUBLE}.
17270 You should use @code{AC_TYPE_LONG_DOUBLE} or
17271 @code{AC_TYPE_LONG_DOUBLE_WIDER} instead. @xref{Particular Types}.
17274 @defmac AC_LONG_FILE_NAMES
17275 @acindex{LONG_FILE_NAMES}
17276 @code{AC_SYS_LONG_FILE_NAMES}
17279 @defmac AC_MAJOR_HEADER
17280 @acindex{MAJOR_HEADER}
17281 @code{AC_HEADER_MAJOR}
17284 @defmac AC_MEMORY_H
17286 @cvindex NEED_MEMORY_H
17287 Used to define @code{NEED_MEMORY_H} if the @code{mem} functions were
17288 defined in @file{memory.h}. Today it is equivalent to
17289 @samp{AC_CHECK_HEADERS([memory.h])}. Adjust your code to depend upon
17290 @code{HAVE_MEMORY_H}, not @code{NEED_MEMORY_H}; see @ref{Standard
17296 Similar to @code{AC_CYGWIN} but checks for the MinGW compiler
17297 environment and sets @code{MINGW32}.
17300 @defmac AC_MINUS_C_MINUS_O
17301 @acindex{MINUS_C_MINUS_O}
17302 @code{AC_PROG_CC_C_O}
17307 @code{AC_FUNC_MMAP}
17312 @code{AC_TYPE_MODE_T}
17318 Defined the output variable @code{OBJEXT} based on the output of the
17319 compiler, after .c files have been excluded. Typically set to @samp{o}
17320 if Posix, @samp{obj} if a @acronym{DOS} variant.
17321 Now the compiler checking macros handle
17322 this automatically.
17325 @defmac AC_OBSOLETE (@var{this-macro-name}, @ovar{suggestion})
17327 Make M4 print a message to the standard error output warning that
17328 @var{this-macro-name} is obsolete, and giving the file and line number
17329 where it was called. @var{this-macro-name} should be the name of the
17330 macro that is calling @code{AC_OBSOLETE}. If @var{suggestion} is given,
17331 it is printed at the end of the warning message; for example, it can be
17332 a suggestion for what to use instead of @var{this-macro-name}.
17337 AC_OBSOLETE([$0], [; use AC_CHECK_HEADERS(unistd.h) instead])dnl
17340 You are encouraged to use @code{AU_DEFUN} instead, since it gives better
17341 services to the user.
17346 @code{AC_TYPE_OFF_T}
17349 @defmac AC_OUTPUT (@ovar{file}@dots{}, @ovar{extra-cmds}, @ovar{init-cmds})
17351 The use of @code{AC_OUTPUT} with argument is deprecated. This obsoleted
17352 interface is equivalent to:
17356 AC_CONFIG_FILES(@var{file}@dots{})
17357 AC_CONFIG_COMMANDS([default],
17358 @var{extra-cmds}, @var{init-cmds})
17364 @defmac AC_OUTPUT_COMMANDS (@var{extra-cmds}, @ovar{init-cmds})
17365 @acindex{OUTPUT_COMMANDS}
17366 Specify additional shell commands to run at the end of
17367 @file{config.status}, and shell commands to initialize any variables
17368 from @command{configure}. This macro may be called multiple times. It is
17369 obsolete, replaced by @code{AC_CONFIG_COMMANDS}.
17371 Here is an unrealistic example:
17375 AC_OUTPUT_COMMANDS([echo this is extra $fubar, and so on.],
17377 AC_OUTPUT_COMMANDS([echo this is another, extra, bit],
17381 Aside from the fact that @code{AC_CONFIG_COMMANDS} requires an
17382 additional key, an important difference is that
17383 @code{AC_OUTPUT_COMMANDS} is quoting its arguments twice, unlike
17384 @code{AC_CONFIG_COMMANDS}. This means that @code{AC_CONFIG_COMMANDS}
17385 can safely be given macro calls as arguments:
17388 AC_CONFIG_COMMANDS(foo, [my_FOO()])
17392 Conversely, where one level of quoting was enough for literal strings
17393 with @code{AC_OUTPUT_COMMANDS}, you need two with
17394 @code{AC_CONFIG_COMMANDS}. The following lines are equivalent:
17398 AC_OUTPUT_COMMANDS([echo "Square brackets: []"])
17399 AC_CONFIG_COMMANDS([default], [[echo "Square brackets: []"]])
17406 @code{AC_TYPE_PID_T}
17411 @code{AC_PREFIX_PROGRAM}
17414 @defmac AC_PROGRAMS_CHECK
17415 @acindex{PROGRAMS_CHECK}
17416 @code{AC_CHECK_PROGS}
17419 @defmac AC_PROGRAMS_PATH
17420 @acindex{PROGRAMS_PATH}
17421 @code{AC_PATH_PROGS}
17424 @defmac AC_PROGRAM_CHECK
17425 @acindex{PROGRAM_CHECK}
17426 @code{AC_CHECK_PROG}
17429 @defmac AC_PROGRAM_EGREP
17430 @acindex{PROGRAM_EGREP}
17431 @code{AC_EGREP_CPP}
17434 @defmac AC_PROGRAM_PATH
17435 @acindex{PROGRAM_PATH}
17436 @code{AC_PATH_PROG}
17439 @defmac AC_REMOTE_TAPE
17440 @acindex{REMOTE_TAPE}
17441 removed because of limited usefulness
17444 @defmac AC_RESTARTABLE_SYSCALLS
17445 @acindex{RESTARTABLE_SYSCALLS}
17446 @code{AC_SYS_RESTARTABLE_SYSCALLS}
17449 @defmac AC_RETSIGTYPE
17450 @acindex{RETSIGTYPE}
17451 @code{AC_TYPE_SIGNAL}
17456 removed because of limited usefulness
17459 @defmac AC_SCO_INTL
17462 If on SCO Unix, add @option{-lintl} to output variable @code{LIBS}. This
17463 macro used to do this:
17466 AC_CHECK_LIB([intl], [strftime], [LIBS="-lintl $LIBS"])
17470 Now it just calls @code{AC_FUNC_STRFTIME} instead.
17473 @defmac AC_SETVBUF_REVERSED
17474 @acindex{SETVBUF_REVERSED}
17475 @code{AC_FUNC_SETVBUF_REVERSED}
17478 @defmac AC_SET_MAKE
17480 @code{AC_PROG_MAKE_SET}
17483 @defmac AC_SIZEOF_TYPE
17484 @acindex{SIZEOF_TYPE}
17485 @code{AC_CHECK_SIZEOF}
17490 @code{AC_TYPE_SIZE_T}
17493 @defmac AC_STAT_MACROS_BROKEN
17494 @acindex{STAT_MACROS_BROKEN}
17495 @code{AC_HEADER_STAT}
17498 @defmac AC_STDC_HEADERS
17499 @acindex{STDC_HEADERS}
17500 @code{AC_HEADER_STDC}
17505 @code{AC_FUNC_STRCOLL}
17508 @defmac AC_ST_BLKSIZE
17509 @acindex{ST_BLKSIZE}
17510 @code{AC_CHECK_MEMBERS}
17513 @defmac AC_ST_BLOCKS
17514 @acindex{ST_BLOCKS}
17515 @code{AC_STRUCT_ST_BLOCKS}
17520 @code{AC_CHECK_MEMBERS}
17523 @defmac AC_SYS_RESTARTABLE_SYSCALLS
17524 @acindex{SYS_RESTARTABLE_SYSCALLS}
17525 @cvindex HAVE_RESTARTABLE_SYSCALLS
17526 If the system automatically restarts a system call that is interrupted
17527 by a signal, define @code{HAVE_RESTARTABLE_SYSCALLS}. This macro does
17528 not check whether system calls are restarted in general---it checks whether a
17529 signal handler installed with @code{signal} (but not @code{sigaction})
17530 causes system calls to be restarted. It does not check whether system calls
17531 can be restarted when interrupted by signals that have no handler.
17533 These days portable programs should use @code{sigaction} with
17534 @code{SA_RESTART} if they want restartable system calls. They should
17535 not rely on @code{HAVE_RESTARTABLE_SYSCALLS}, since nowadays whether a
17536 system call is restartable is a dynamic issue, not a configuration-time
17540 @defmac AC_SYS_SIGLIST_DECLARED
17541 @acindex{SYS_SIGLIST_DECLARED}
17542 @code{AC_DECL_SYS_SIGLIST}
17545 @defmac AC_TEST_CPP
17547 @code{AC_TRY_CPP}, replaced by @code{AC_PREPROC_IFELSE}.
17550 @defmac AC_TEST_PROGRAM
17551 @acindex{TEST_PROGRAM}
17552 @code{AC_TRY_RUN}, replaced by @code{AC_RUN_IFELSE}.
17555 @defmac AC_TIMEZONE
17557 @code{AC_STRUCT_TIMEZONE}
17560 @defmac AC_TIME_WITH_SYS_TIME
17561 @acindex{TIME_WITH_SYS_TIME}
17562 @code{AC_HEADER_TIME}
17565 @defmac AC_TRY_COMPILE (@var{includes}, @var{function-body}, @ovar{action-if-true}, @ovar{action-if-false})
17566 @acindex{TRY_COMPILE}
17571 [AC_LANG_PROGRAM([[@var{includes}]],
17572 [[@var{function-body}]])],
17573 [@var{action-if-true}],
17574 [@var{action-if-false}])
17578 @xref{Running the Compiler}.
17580 This macro double quotes both @var{includes} and @var{function-body}.
17582 For C and C++, @var{includes} is any @code{#include} statements needed
17583 by the code in @var{function-body} (@var{includes} is ignored if
17584 the currently selected language is Fortran or Fortran 77). The compiler
17585 and compilation flags are determined by the current language
17586 (@pxref{Language Choice}).
17589 @defmac AC_TRY_CPP (@var{input}, @ovar{action-if-true}, @ovar{action-if-false})
17595 [AC_LANG_SOURCE([[@var{input}]])],
17596 [@var{action-if-true}],
17597 [@var{action-if-false}])
17601 @xref{Running the Preprocessor}.
17603 This macro double quotes the @var{input}.
17606 @defmac AC_TRY_LINK (@var{includes}, @var{function-body}, @ovar{action-if-true}, @ovar{action-if-false})
17612 [AC_LANG_PROGRAM([[@var{includes}]],
17613 [[@var{function-body}]])],
17614 [@var{action-if-true}],
17615 [@var{action-if-false}])
17619 @xref{Running the Compiler}.
17621 This macro double quotes both @var{includes} and @var{function-body}.
17623 Depending on the current language (@pxref{Language Choice}), create a
17624 test program to see whether a function whose body consists of
17625 @var{function-body} can be compiled and linked. If the file compiles
17626 and links successfully, run shell commands @var{action-if-found},
17627 otherwise run @var{action-if-not-found}.
17629 This macro double quotes both @var{includes} and @var{function-body}.
17631 For C and C++, @var{includes} is any @code{#include} statements needed
17632 by the code in @var{function-body} (@var{includes} is ignored if
17633 the currently selected language is Fortran or Fortran 77). The compiler
17634 and compilation flags are determined by the current language
17635 (@pxref{Language Choice}), and in addition @code{LDFLAGS} and
17636 @code{LIBS} are used for linking.
17639 @defmac AC_TRY_LINK_FUNC (@var{function}, @ovar{action-if-found}, @ovar{action-if-not-found})
17640 @acindex{TRY_LINK_FUNC}
17641 This macro is equivalent to
17642 @samp{AC_LINK_IFELSE([AC_LANG_CALL([], [@var{function}])],
17643 [@var{action-if-found}], [@var{action-if-not-found}])}.
17646 @defmac AC_TRY_RUN (@var{program}, @ovar{action-if-true}, @ovar{action-if-false}, @ovar{action-if-cross-compiling})
17652 [AC_LANG_SOURCE([[@var{program}]])],
17653 [@var{action-if-true}],
17654 [@var{action-if-false}],
17655 [@var{action-if-cross-compiling}])
17664 @code{AC_TYPE_UID_T}
17667 @defmac AC_UNISTD_H
17669 Same as @samp{AC_CHECK_HEADERS([unistd.h])}.
17675 Define @code{USG} if the @acronym{BSD} string functions are defined in
17676 @file{strings.h}. You should no longer depend upon @code{USG}, but on
17677 @code{HAVE_STRING_H}; see @ref{Standard Symbols}.
17680 @defmac AC_UTIME_NULL
17681 @acindex{UTIME_NULL}
17682 @code{AC_FUNC_UTIME_NULL}
17685 @defmac AC_VALIDATE_CACHED_SYSTEM_TUPLE (@ovar{cmd})
17686 @acindex{VALIDATE_CACHED_SYSTEM_TUPLE}
17687 If the cache file is inconsistent with the current host, target and
17688 build system types, it used to execute @var{cmd} or print a default
17689 error message. This is now handled by default.
17692 @defmac AC_VERBOSE (@var{result-description})
17694 @code{AC_MSG_RESULT}.
17699 @code{AC_FUNC_VFORK}
17704 @code{AC_FUNC_VPRINTF}
17709 @code{AC_FUNC_WAIT3}
17717 @defmac AC_WORDS_BIGENDIAN
17718 @acindex{WORDS_BIGENDIAN}
17719 @code{AC_C_BIGENDIAN}
17722 @defmac AC_XENIX_DIR
17723 @acindex{XENIX_DIR}
17725 This macro used to add @option{-lx} to output variable @code{LIBS} if on
17726 Xenix. Also, if @file{dirent.h} is being checked for, added
17727 @option{-ldir} to @code{LIBS}. Now it is merely an alias of
17728 @code{AC_HEADER_DIRENT} instead, plus some code to detect whether
17729 running @sc{xenix} on which you should not depend:
17732 AC_MSG_CHECKING([for Xenix])
17733 AC_EGREP_CPP([yes],
17734 [#if defined M_XENIX && !defined M_UNIX
17737 [AC_MSG_RESULT([yes]); XENIX=yes],
17738 [AC_MSG_RESULT([no]); XENIX=])
17742 @defmac AC_YYTEXT_POINTER
17743 @acindex{YYTEXT_POINTER}
17744 @code{AC_DECL_YYTEXT}
17748 @section Upgrading From Version 1
17749 @cindex Upgrading autoconf
17750 @cindex Autoconf upgrading
17752 Autoconf version 2 is mostly backward compatible with version 1.
17753 However, it introduces better ways to do some things, and doesn't
17754 support some of the ugly things in version 1. So, depending on how
17755 sophisticated your @file{configure.ac} files are, you might have to do
17756 some manual work in order to upgrade to version 2. This chapter points
17757 out some problems to watch for when upgrading. Also, perhaps your
17758 @command{configure} scripts could benefit from some of the new features in
17759 version 2; the changes are summarized in the file @file{NEWS} in the
17760 Autoconf distribution.
17763 * Changed File Names:: Files you might rename
17764 * Changed Makefiles:: New things to put in @file{Makefile.in}
17765 * Changed Macros:: Macro calls you might replace
17766 * Changed Results:: Changes in how to check test results
17767 * Changed Macro Writing:: Better ways to write your own macros
17770 @node Changed File Names
17771 @subsection Changed File Names
17773 If you have an @file{aclocal.m4} installed with Autoconf (as opposed to
17774 in a particular package's source directory), you must rename it to
17775 @file{acsite.m4}. @xref{autoconf Invocation}.
17777 If you distribute @file{install.sh} with your package, rename it to
17778 @file{install-sh} so @code{make} builtin rules don't inadvertently
17779 create a file called @file{install} from it. @code{AC_PROG_INSTALL}
17780 looks for the script under both names, but it is best to use the new name.
17782 If you were using @file{config.h.top}, @file{config.h.bot}, or
17783 @file{acconfig.h}, you still can, but you have less clutter if you
17784 use the @code{AH_} macros. @xref{Autoheader Macros}.
17786 @node Changed Makefiles
17787 @subsection Changed Makefiles
17789 Add @samp{@@CFLAGS@@}, @samp{@@CPPFLAGS@@}, and @samp{@@LDFLAGS@@} in
17790 your @file{Makefile.in} files, so they can take advantage of the values
17791 of those variables in the environment when @command{configure} is run.
17792 Doing this isn't necessary, but it's a convenience for users.
17794 Also add @samp{@@configure_input@@} in a comment to each input file for
17795 @code{AC_OUTPUT}, so that the output files contain a comment saying
17796 they were produced by @command{configure}. Automatically selecting the
17797 right comment syntax for all the kinds of files that people call
17798 @code{AC_OUTPUT} on became too much work.
17800 Add @file{config.log} and @file{config.cache} to the list of files you
17801 remove in @code{distclean} targets.
17803 If you have the following in @file{Makefile.in}:
17806 prefix = /usr/local
17807 exec_prefix = $(prefix)
17811 you must change it to:
17814 prefix = @@prefix@@
17815 exec_prefix = @@exec_prefix@@
17819 The old behavior of replacing those variables without @samp{@@}
17820 characters around them has been removed.
17822 @node Changed Macros
17823 @subsection Changed Macros
17825 Many of the macros were renamed in Autoconf version 2. You can still
17826 use the old names, but the new ones are clearer, and it's easier to find
17827 the documentation for them. @xref{Obsolete Macros}, for a table showing the
17828 new names for the old macros. Use the @command{autoupdate} program to
17829 convert your @file{configure.ac} to using the new macro names.
17830 @xref{autoupdate Invocation}.
17832 Some macros have been superseded by similar ones that do the job better,
17833 but are not call-compatible. If you get warnings about calling obsolete
17834 macros while running @command{autoconf}, you may safely ignore them, but
17835 your @command{configure} script generally works better if you follow
17836 the advice that is printed about what to replace the obsolete macros with. In
17837 particular, the mechanism for reporting the results of tests has
17838 changed. If you were using @command{echo} or @code{AC_VERBOSE} (perhaps
17839 via @code{AC_COMPILE_CHECK}), your @command{configure} script's output
17840 looks better if you switch to @code{AC_MSG_CHECKING} and
17841 @code{AC_MSG_RESULT}. @xref{Printing Messages}. Those macros work best
17842 in conjunction with cache variables. @xref{Caching Results}.
17846 @node Changed Results
17847 @subsection Changed Results
17849 If you were checking the results of previous tests by examining the
17850 shell variable @code{DEFS}, you need to switch to checking the values of
17851 the cache variables for those tests. @code{DEFS} no longer exists while
17852 @command{configure} is running; it is only created when generating output
17853 files. This difference from version 1 is because properly quoting the
17854 contents of that variable turned out to be too cumbersome and
17855 inefficient to do every time @code{AC_DEFINE} is called. @xref{Cache
17858 For example, here is a @file{configure.ac} fragment written for Autoconf
17862 AC_HAVE_FUNCS(syslog)
17864 *-DHAVE_SYSLOG*) ;;
17865 *) # syslog is not in the default libraries. See if it's in some other.
17867 for lib in bsd socket inet; do
17868 AC_CHECKING(for syslog in -l$lib)
17869 LIBS="-l$lib $saved_LIBS"
17870 AC_HAVE_FUNCS(syslog)
17872 *-DHAVE_SYSLOG*) break ;;
17880 Here is a way to write it for version 2:
17883 AC_CHECK_FUNCS([syslog])
17884 if test $ac_cv_func_syslog = no; then
17885 # syslog is not in the default libraries. See if it's in some other.
17886 for lib in bsd socket inet; do
17887 AC_CHECK_LIB([$lib], [syslog], [AC_DEFINE([HAVE_SYSLOG])
17888 LIBS="-l$lib $LIBS"; break])
17893 If you were working around bugs in @code{AC_DEFINE_UNQUOTED} by adding
17894 backslashes before quotes, you need to remove them. It now works
17895 predictably, and does not treat quotes (except back quotes) specially.
17896 @xref{Setting Output Variables}.
17898 All of the Boolean shell variables set by Autoconf macros now use
17899 @samp{yes} for the true value. Most of them use @samp{no} for false,
17900 though for backward compatibility some use the empty string instead. If
17901 you were relying on a shell variable being set to something like 1 or
17902 @samp{t} for true, you need to change your tests.
17904 @node Changed Macro Writing
17905 @subsection Changed Macro Writing
17907 When defining your own macros, you should now use @code{AC_DEFUN}
17908 instead of @code{define}. @code{AC_DEFUN} automatically calls
17909 @code{AC_PROVIDE} and ensures that macros called via @code{AC_REQUIRE}
17910 do not interrupt other macros, to prevent nested @samp{checking@dots{}}
17911 messages on the screen. There's no actual harm in continuing to use the
17912 older way, but it's less convenient and attractive. @xref{Macro
17915 You probably looked at the macros that came with Autoconf as a guide for
17916 how to do things. It would be a good idea to take a look at the new
17917 versions of them, as the style is somewhat improved and they take
17918 advantage of some new features.
17920 If you were doing tricky things with undocumented Autoconf internals
17921 (macros, variables, diversions), check whether you need to change
17922 anything to account for changes that have been made. Perhaps you can
17923 even use an officially supported technique in version 2 instead of
17924 kludging. Or perhaps not.
17926 To speed up your locally written feature tests, add caching to them.
17927 See whether any of your tests are of general enough usefulness to
17928 encapsulate them into macros that you can share.
17931 @node Autoconf 2.13
17932 @section Upgrading From Version 2.13
17933 @cindex Upgrading autoconf
17934 @cindex Autoconf upgrading
17936 The introduction of the previous section (@pxref{Autoconf 1}) perfectly
17937 suits this section@enddots{}
17940 Autoconf version 2.50 is mostly backward compatible with version 2.13.
17941 However, it introduces better ways to do some things, and doesn't
17942 support some of the ugly things in version 2.13. So, depending on how
17943 sophisticated your @file{configure.ac} files are, you might have to do
17944 some manual work in order to upgrade to version 2.50. This chapter
17945 points out some problems to watch for when upgrading. Also, perhaps
17946 your @command{configure} scripts could benefit from some of the new
17947 features in version 2.50; the changes are summarized in the file
17948 @file{NEWS} in the Autoconf distribution.
17952 * Changed Quotation:: Broken code which used to work
17953 * New Macros:: Interaction with foreign macros
17954 * Hosts and Cross-Compilation:: Bugward compatibility kludges
17955 * AC_LIBOBJ vs LIBOBJS:: LIBOBJS is a forbidden token
17956 * AC_FOO_IFELSE vs AC_TRY_FOO:: A more generic scheme for testing sources
17959 @node Changed Quotation
17960 @subsection Changed Quotation
17962 The most important changes are invisible to you: the implementation of
17963 most macros have completely changed. This allowed more factorization of
17964 the code, better error messages, a higher uniformity of the user's
17965 interface etc. Unfortunately, as a side effect, some construct which
17966 used to (miraculously) work might break starting with Autoconf 2.50.
17967 The most common culprit is bad quotation.
17969 For instance, in the following example, the message is not properly
17974 AC_CHECK_HEADERS(foo.h, ,
17975 AC_MSG_ERROR(cannot find foo.h, bailing out))
17980 Autoconf 2.13 simply ignores it:
17983 $ @kbd{autoconf-2.13; ./configure --silent}
17984 creating cache ./config.cache
17985 configure: error: cannot find foo.h
17990 while Autoconf 2.50 produces a broken @file{configure}:
17993 $ @kbd{autoconf-2.50; ./configure --silent}
17994 configure: error: cannot find foo.h
17995 ./configure: exit: bad non-numeric arg `bailing'
17996 ./configure: exit: bad non-numeric arg `bailing'
18000 The message needs to be quoted, and the @code{AC_MSG_ERROR} invocation
18004 AC_INIT([Example], [1.0], [bug-example@@example.org])
18005 AC_CHECK_HEADERS([foo.h], [],
18006 [AC_MSG_ERROR([cannot find foo.h, bailing out])])
18010 Many many (and many more) Autoconf macros were lacking proper quotation,
18011 including no less than@dots{} @code{AC_DEFUN} itself!
18014 $ @kbd{cat configure.in}
18015 AC_DEFUN([AC_PROG_INSTALL],
18016 [# My own much better version
18021 $ @kbd{autoconf-2.13}
18022 autoconf: Undefined macros:
18023 ***BUG in Autoconf--please report*** AC_FD_MSG
18024 ***BUG in Autoconf--please report*** AC_EPI
18025 configure.in:1:AC_DEFUN([AC_PROG_INSTALL],
18026 configure.in:5:AC_PROG_INSTALL
18027 $ @kbd{autoconf-2.50}
18033 @subsection New Macros
18035 @cindex undefined macro
18036 @cindex @code{_m4_divert_diversion}
18038 While Autoconf was relatively dormant in the late 1990s, Automake
18039 provided Autoconf-like macros for a while. Starting with Autoconf 2.50
18040 in 2001, Autoconf provided
18041 versions of these macros, integrated in the @code{AC_} namespace,
18042 instead of @code{AM_}. But in order to ease the upgrading via
18043 @command{autoupdate}, bindings to such @code{AM_} macros are provided.
18045 Unfortunately older versions of Automake (e.g., Automake 1.4)
18046 did not quote the names of these macros.
18047 Therefore, when @command{m4} finds something like
18048 @samp{AC_DEFUN(AM_TYPE_PTRDIFF_T, @dots{})} in @file{aclocal.m4},
18049 @code{AM_TYPE_PTRDIFF_T} is
18050 expanded, replaced with its Autoconf definition.
18052 Fortunately Autoconf catches pre-@code{AC_INIT} expansions, and
18053 complains, in its own words:
18056 $ @kbd{cat configure.ac}
18057 AC_INIT([Example], [1.0], [bug-example@@example.org])
18059 $ @kbd{aclocal-1.4}
18061 aclocal.m4:17: error: m4_defn: undefined macro: _m4_divert_diversion
18062 aclocal.m4:17: the top level
18063 autom4te: m4 failed with exit status: 1
18067 Modern versions of Automake no longer define most of these
18068 macros, and properly quote the names of the remaining macros.
18069 If you must use an old Automake, do not depend upon macros from Automake
18070 as it is simply not its job
18071 to provide macros (but the one it requires itself):
18074 $ @kbd{cat configure.ac}
18075 AC_INIT([Example], [1.0], [bug-example@@example.org])
18077 $ @kbd{rm aclocal.m4}
18079 autoupdate: `configure.ac' is updated
18080 $ @kbd{cat configure.ac}
18081 AC_INIT([Example], [1.0], [bug-example@@example.org])
18082 AC_CHECK_TYPES([ptrdiff_t])
18083 $ @kbd{aclocal-1.4}
18089 @node Hosts and Cross-Compilation
18090 @subsection Hosts and Cross-Compilation
18091 @cindex Cross compilation
18093 Based on the experience of compiler writers, and after long public
18094 debates, many aspects of the cross-compilation chain have changed:
18098 the relationship between the build, host, and target architecture types,
18101 the command line interface for specifying them to @command{configure},
18104 the variables defined in @command{configure},
18107 the enabling of cross-compilation mode.
18112 The relationship between build, host, and target have been cleaned up:
18113 the chain of default is now simply: target defaults to host, host to
18114 build, and build to the result of @command{config.guess}. Nevertheless,
18115 in order to ease the transition from 2.13 to 2.50, the following
18116 transition scheme is implemented. @emph{Do not rely on it}, as it will
18117 be completely disabled in a couple of releases (we cannot keep it, as it
18118 proves to cause more problems than it cures).
18120 They all default to the result of running @command{config.guess}, unless
18121 you specify either @option{--build} or @option{--host}. In this case,
18122 the default becomes the system type you specified. If you specify both,
18123 and they're different, @command{configure} enters cross compilation
18124 mode, so it doesn't run any tests that require execution.
18126 Hint: if you mean to override the result of @command{config.guess},
18127 prefer @option{--build} over @option{--host}. In the future,
18128 @option{--host} will not override the name of the build system type.
18129 Whenever you specify @option{--host}, be sure to specify @option{--build}
18134 For backward compatibility, @command{configure} accepts a system
18135 type as an option by itself. Such an option overrides the
18136 defaults for build, host, and target system types. The following
18137 configure statement configures a cross toolchain that runs on
18138 Net@acronym{BSD}/alpha but generates code for @acronym{GNU} Hurd/sparc,
18139 which is also the build platform.
18142 ./configure --host=alpha-netbsd sparc-gnu
18147 In Autoconf 2.13 and before, the variables @code{build}, @code{host},
18148 and @code{target} had a different semantics before and after the
18149 invocation of @code{AC_CANONICAL_BUILD} etc. Now, the argument of
18150 @option{--build} is strictly copied into @code{build_alias}, and is left
18151 empty otherwise. After the @code{AC_CANONICAL_BUILD}, @code{build} is
18152 set to the canonicalized build type. To ease the transition, before,
18153 its contents is the same as that of @code{build_alias}. Do @emph{not}
18154 rely on this broken feature.
18156 For consistency with the backward compatibility scheme exposed above,
18157 when @option{--host} is specified but @option{--build} isn't, the build
18158 system is assumed to be the same as @option{--host}, and
18159 @samp{build_alias} is set to that value. Eventually, this
18160 historically incorrect behavior will go away.
18164 The former scheme to enable cross-compilation proved to cause more harm
18165 than good, in particular, it used to be triggered too easily, leaving
18166 regular end users puzzled in front of cryptic error messages.
18167 @command{configure} could even enter cross-compilation mode only
18168 because the compiler was not functional. This is mainly because
18169 @command{configure} used to try to detect cross-compilation, instead of
18170 waiting for an explicit flag from the user.
18172 Now, @command{configure} enters cross-compilation mode if and only if
18173 @option{--host} is passed.
18175 That's the short documentation. To ease the transition between 2.13 and
18176 its successors, a more complicated scheme is implemented. @emph{Do not
18177 rely on the following}, as it will be removed in the near future.
18179 If you specify @option{--host}, but not @option{--build}, when
18180 @command{configure} performs the first compiler test it tries to run
18181 an executable produced by the compiler. If the execution fails, it
18182 enters cross-compilation mode. This is fragile. Moreover, by the time
18183 the compiler test is performed, it may be too late to modify the
18184 build-system type: other tests may have already been performed.
18185 Therefore, whenever you specify @option{--host}, be sure to specify
18186 @option{--build} too.
18189 ./configure --build=i686-pc-linux-gnu --host=m68k-coff
18193 enters cross-compilation mode. The former interface, which
18194 consisted in setting the compiler to a cross-compiler without informing
18195 @command{configure} is obsolete. For instance, @command{configure}
18196 fails if it can't run the code generated by the specified compiler if you
18197 configure as follows:
18200 ./configure CC=m68k-coff-gcc
18204 @node AC_LIBOBJ vs LIBOBJS
18205 @subsection @code{AC_LIBOBJ} vs.@: @code{LIBOBJS}
18207 Up to Autoconf 2.13, the replacement of functions was triggered via the
18208 variable @code{LIBOBJS}. Since Autoconf 2.50, the macro
18209 @code{AC_LIBOBJ} should be used instead (@pxref{Generic Functions}).
18210 Starting at Autoconf 2.53, the use of @code{LIBOBJS} is an error.
18212 This change is mandated by the unification of the @acronym{GNU} Build System
18213 components. In particular, the various fragile techniques used to parse
18214 a @file{configure.ac} are all replaced with the use of traces. As a
18215 consequence, any action must be traceable, which obsoletes critical
18216 variable assignments. Fortunately, @code{LIBOBJS} was the only problem,
18217 and it can even be handled gracefully (read, ``without your having to
18218 change something'').
18220 There were two typical uses of @code{LIBOBJS}: asking for a replacement
18221 function, and adjusting @code{LIBOBJS} for Automake and/or Libtool.
18225 As for function replacement, the fix is immediate: use
18226 @code{AC_LIBOBJ}. For instance:
18229 LIBOBJS="$LIBOBJS fnmatch.o"
18230 LIBOBJS="$LIBOBJS malloc.$ac_objext"
18234 should be replaced with:
18237 AC_LIBOBJ([fnmatch])
18238 AC_LIBOBJ([malloc])
18244 When used with Automake 1.10 or newer, a suitable value for
18245 @code{LIBOBJDIR} is set so that the @code{LIBOBJS} and @code{LTLIBOBJS}
18246 can be referenced from any @file{Makefile.am}. Even without Automake,
18247 arranging for @code{LIBOBJDIR} to be set correctly enables
18248 referencing @code{LIBOBJS} and @code{LTLIBOBJS} in another directory.
18249 The @code{LIBOBJDIR} feature is experimental.
18252 @node AC_FOO_IFELSE vs AC_TRY_FOO
18253 @subsection @code{AC_FOO_IFELSE} vs.@: @code{AC_TRY_FOO}
18255 Since Autoconf 2.50, internal codes uses @code{AC_PREPROC_IFELSE},
18256 @code{AC_COMPILE_IFELSE}, @code{AC_LINK_IFELSE}, and
18257 @code{AC_RUN_IFELSE} on one hand and @code{AC_LANG_SOURCES},
18258 and @code{AC_LANG_PROGRAM} on the other hand instead of the deprecated
18259 @code{AC_TRY_CPP}, @code{AC_TRY_COMPILE}, @code{AC_TRY_LINK}, and
18260 @code{AC_TRY_RUN}. The motivations where:
18263 a more consistent interface: @code{AC_TRY_COMPILE} etc.@: were double
18264 quoting their arguments;
18267 the combinatoric explosion is solved by decomposing on the one hand the
18268 generation of sources, and on the other hand executing the program;
18271 this scheme helps supporting more languages than plain C and C++.
18274 In addition to the change of syntax, the philosophy has changed too:
18275 while emphasis was put on speed at the expense of accuracy, today's
18276 Autoconf promotes accuracy of the testing framework at, ahem@dots{}, the
18280 As a perfect example of what is @emph{not} to be done, here is how to
18281 find out whether a header file contains a particular declaration, such
18282 as a typedef, a structure, a structure member, or a function. Use
18283 @code{AC_EGREP_HEADER} instead of running @code{grep} directly on the
18284 header file; on some systems the symbol might be defined in another
18285 header file that the file you are checking includes.
18287 As a (bad) example, here is how you should not check for C preprocessor
18288 symbols, either defined by header files or predefined by the C
18289 preprocessor: using @code{AC_EGREP_CPP}:
18297 ], is_aix=yes, is_aix=no)
18301 The above example, properly written would (i) use
18302 @code{AC_LANG_PROGRAM}, and (ii) run the compiler:
18306 AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
18308 error: This isn't AIX!
18317 @c ============================= Generating Test Suites with Autotest
18319 @node Using Autotest
18320 @chapter Generating Test Suites with Autotest
18325 @strong{N.B.: This section describes an experimental feature which will
18326 be part of Autoconf in a forthcoming release. Although we believe
18327 Autotest is stabilizing, this documentation describes an interface which
18328 might change in the future: do not depend upon Autotest without
18329 subscribing to the Autoconf mailing lists.}
18332 It is paradoxical that portable projects depend on nonportable tools
18333 to run their test suite. Autoconf by itself is the paragon of this
18334 problem: although it aims at perfectly portability, up to 2.13 its
18335 test suite was using Deja@acronym{GNU}, a rich and complex testing
18336 framework, but which is far from being standard on Posix systems.
18337 Worse yet, it was likely to be missing on the most fragile platforms,
18338 the very platforms that are most likely to torture Autoconf and
18339 exhibit deficiencies.
18341 To circumvent this problem, many package maintainers have developed their
18342 own testing framework, based on simple shell scripts whose sole outputs
18343 are exit status values describing whether the test succeeded. Most of
18344 these tests share common patterns, and this can result in lots of
18345 duplicated code and tedious maintenance.
18347 Following exactly the same reasoning that yielded to the inception of
18348 Autoconf, Autotest provides a test suite generation framework, based on
18349 M4 macros building a portable shell script. The suite itself is
18350 equipped with automatic logging and tracing facilities which greatly
18351 diminish the interaction with bug reporters, and simple timing reports.
18353 Autoconf itself has been using Autotest for years, and we do attest that
18354 it has considerably improved the strength of the test suite and the
18355 quality of bug reports. Other projects are known to use some generation
18356 of Autotest, such as Bison, Free Recode, Free Wdiff, @acronym{GNU} Tar, each of
18357 them with different needs, and this usage has validated Autotest as a general
18360 Nonetheless, compared to Deja@acronym{GNU}, Autotest is inadequate for
18361 interactive tool testing, which is probably its main limitation.
18364 * Using an Autotest Test Suite:: Autotest and the user
18365 * Writing Testsuites:: Autotest macros
18366 * testsuite Invocation:: Running @command{testsuite} scripts
18367 * Making testsuite Scripts:: Using autom4te to create @command{testsuite}
18370 @node Using an Autotest Test Suite
18371 @section Using an Autotest Test Suite
18374 * testsuite Scripts:: The concepts of Autotest
18375 * Autotest Logs:: Their contents
18378 @node testsuite Scripts
18379 @subsection @command{testsuite} Scripts
18381 @cindex @command{testsuite}
18383 Generating testing or validation suites using Autotest is rather easy.
18384 The whole validation suite is held in a file to be processed through
18385 @command{autom4te}, itself using @acronym{GNU} M4 under the scene, to
18386 produce a stand-alone Bourne shell script which then gets distributed.
18387 Neither @command{autom4te} nor @acronym{GNU} M4 are needed at
18388 the installer's end.
18391 Each test of the validation suite should be part of some test group. A
18392 @dfn{test group} is a sequence of interwoven tests that ought to be
18393 executed together, usually because one test in the group creates data
18394 files than a later test in the same group needs to read. Complex test
18395 groups make later debugging more tedious. It is much better to
18396 keep only a few tests per test group. Ideally there is only one test
18399 For all but the simplest packages, some file such as @file{testsuite.at}
18400 does not fully hold all test sources, as these are often easier to
18401 maintain in separate files. Each of these separate files holds a single
18402 test group, or a sequence of test groups all addressing some common
18403 functionality in the package. In such cases, @file{testsuite.at}
18404 merely initializes the validation suite, and sometimes does elementary
18405 health checking, before listing include statements for all other test
18406 files. The special file @file{package.m4}, containing the
18407 identification of the package, is automatically included if found.
18409 A convenient alternative consists in moving all the global issues
18410 (local Autotest macros, elementary health checking, and @code{AT_INIT}
18411 invocation) into the file @code{local.at}, and making
18412 @file{testsuite.at} be a simple list of @code{m4_include} of sub test
18413 suites. In such case, generating the whole test suite or pieces of it
18414 is only a matter of choosing the @command{autom4te} command line
18417 The validation scripts that Autotest produces are by convention called
18418 @command{testsuite}. When run, @command{testsuite} executes each test
18419 group in turn, producing only one summary line per test to say if that
18420 particular test succeeded or failed. At end of all tests, summarizing
18421 counters get printed. One debugging directory is left for each test
18422 group which failed, if any: such directories are named
18423 @file{testsuite.dir/@var{nn}}, where @var{nn} is the sequence number of
18424 the test group, and they include:
18427 @item a debugging script named @file{run} which reruns the test in
18428 @dfn{debug mode} (@pxref{testsuite Invocation}). The automatic generation
18429 of debugging scripts has the purpose of easing the chase for bugs.
18431 @item all the files created with @code{AT_DATA}
18433 @item a log of the run, named @file{testsuite.log}
18436 In the ideal situation, none of the tests fail, and consequently no
18437 debugging directory is left behind for validation.
18439 It often happens in practice that individual tests in the validation
18440 suite need to get information coming out of the configuration process.
18441 Some of this information, common for all validation suites, is provided
18442 through the file @file{atconfig}, automatically created by
18443 @code{AC_CONFIG_TESTDIR}. For configuration informations which your
18444 testing environment specifically needs, you might prepare an optional
18445 file named @file{atlocal.in}, instantiated by @code{AC_CONFIG_FILES}.
18446 The configuration process produces @file{atconfig} and @file{atlocal}
18447 out of these two input files, and these two produced files are
18448 automatically read by the @file{testsuite} script.
18450 Here is a diagram showing the relationship between files.
18453 Files used in preparing a software package for distribution:
18458 subfile-1.at ->. [local.at] ---->+
18460 subfile-i.at ---->-- testsuite.at -->-- autom4te* -->testsuite
18466 Files used in configuring a software package:
18471 [atlocal.in] --> config.status* --<
18477 Files created during the test suite execution:
18480 atconfig -->. .--> testsuite.log
18484 [atlocal] ->' `--> [testsuite.dir]
18488 @node Autotest Logs
18489 @subsection Autotest Logs
18491 When run, the test suite creates a log file named after itself, e.g., a
18492 test suite named @command{testsuite} creates @file{testsuite.log}. It
18493 contains a lot of information, usually more than maintainers actually
18494 need, but therefore most of the time it contains all that is needed:
18497 @item command line arguments
18498 @c akim s/to consist in/to consist of/
18499 A bad but unfortunately widespread habit consists of
18500 setting environment variables before the command, such as in
18501 @samp{CC=my-home-grown-cc ./testsuite}. The test suite does not
18502 know this change, hence (i) it cannot report it to you, and (ii)
18503 it cannot preserve the value of @code{CC} for subsequent runs.
18504 Autoconf faced exactly the same problem, and solved it by asking
18505 users to pass the variable definitions as command line arguments.
18506 Autotest requires this rule, too, but has no means to enforce it; the log
18507 then contains a trace of the variables that were changed by the user.
18509 @item @file{ChangeLog} excerpts
18510 The topmost lines of all the @file{ChangeLog} files found in the source
18511 hierarchy. This is especially useful when bugs are reported against
18512 development versions of the package, since the version string does not
18513 provide sufficient information to know the exact state of the sources
18514 the user compiled. Of course, this relies on the use of a
18517 @item build machine
18518 Running a test suite in a cross-compile environment is not an easy task,
18519 since it would mean having the test suite run on a machine @var{build},
18520 while running programs on a machine @var{host}. It is much simpler to
18521 run both the test suite and the programs on @var{host}, but then, from
18522 the point of view of the test suite, there remains a single environment,
18523 @var{host} = @var{build}. The log contains relevant information on the
18524 state of the build machine, including some important environment
18526 @c FIXME: How about having an M4sh macro to say `hey, log the value
18527 @c of `@dots{}'? This would help both Autoconf and Autotest.
18529 @item tested programs
18530 The absolute file name and answers to @option{--version} of the tested
18531 programs (see @ref{Writing Testsuites}, @code{AT_TESTED}).
18533 @item configuration log
18534 The contents of @file{config.log}, as created by @command{configure},
18535 are appended. It contains the configuration flags and a detailed report
18536 on the configuration itself.
18540 @node Writing Testsuites
18541 @section Writing @file{testsuite.at}
18543 The @file{testsuite.at} is a Bourne shell script making use of special
18544 Autotest M4 macros. It often contains a call to @code{AT_INIT} near
18545 its beginning followed by one call to @code{m4_include} per source file
18546 for tests. Each such included file, or the remainder of
18547 @file{testsuite.at} if include files are not used, contain a sequence of
18548 test groups. Each test group begins with a call to @code{AT_SETUP},
18549 then an arbitrary number of shell commands or calls to @code{AT_CHECK},
18550 and then completes with a call to @code{AT_CLEANUP}.
18552 @defmac AT_INIT (@ovar{name})
18554 @c FIXME: Not clear, plus duplication of the information.
18555 Initialize Autotest. Giving a @var{name} to the test suite is
18556 encouraged if your package includes several test suites. In any case,
18557 the test suite always displays the package name and version. It also
18558 inherits the package bug report address.
18561 @defmac AT_COPYRIGHT (@var{copyright-notice})
18562 @atindex{COPYRIGHT}
18563 @cindex Copyright Notice
18564 State that, in addition to the Free Software Foundation's copyright on
18565 the Autotest macros, parts of your test suite are covered by
18566 @var{copyright-notice}.
18568 The @var{copyright-notice} shows up in both the head of
18569 @command{testsuite} and in @samp{testsuite --version}.
18572 @defmac AT_TESTED (@var{executables})
18574 Log the file name and answer to @option{--version} of each program in
18575 space-separated list @var{executables}. Several invocations register
18576 new executables, in other words, don't fear registering one program
18580 Autotest test suites rely on @env{PATH} to find the tested program.
18581 This avoids the need to generate absolute names of the various tools, and
18582 makes it possible to test installed programs. Therefore, knowing which
18583 programs are being exercised is crucial to understanding problems in
18584 the test suite itself, or its occasional misuses. It is a good idea to
18585 also subscribe foreign programs you depend upon, to avoid incompatible
18590 @defmac AT_SETUP (@var{test-group-name})
18592 This macro starts a group of related tests, all to be executed in the
18593 same subshell. It accepts a single argument, which holds a few words
18594 (no more than about 30 or 40 characters) quickly describing the purpose
18595 of the test group being started.
18598 @defmac AT_KEYWORDS (@var{keywords})
18600 Associate the space-separated list of @var{keywords} to the enclosing
18601 test group. This makes it possible to run ``slices'' of the test suite.
18602 For instance, if some of your test groups exercise some @samp{foo}
18603 feature, then using @samp{AT_KEYWORDS(foo)} lets you run
18604 @samp{./testsuite -k foo} to run exclusively these test groups. The
18605 @var{title} of the test group is automatically recorded to
18606 @code{AT_KEYWORDS}.
18608 Several invocations within a test group accumulate new keywords. In
18609 other words, don't fear registering the same keyword several times in a
18613 @defmac AT_CAPTURE_FILE (@var{file})
18614 @atindex{CAPTURE_FILE}
18615 If the current test group fails, log the contents of @var{file}.
18616 Several identical calls within one test group have no additional effect.
18619 @defmac AT_XFAIL_IF (@var{shell-condition})
18621 Determine whether the test is expected to fail because it is a known
18622 bug (for unsupported features, you should skip the test).
18623 @var{shell-condition} is a shell expression such as a @code{test}
18624 command; you can instantiate this macro many times from within the
18625 same test group, and one of the conditions is enough to turn
18626 the test into an expected failure.
18631 End the current test group.
18636 @defmac AT_DATA (@var{file}, @var{contents})
18638 Initialize an input data @var{file} with given @var{contents}. Of
18639 course, the @var{contents} have to be properly quoted between square
18640 brackets to protect against included commas or spurious M4
18641 expansion. The contents ought to end with an end of line.
18644 @defmac AT_CHECK (@var{commands}, @dvar{status, 0}, @dvar{stdout, }, @dvar{stderr, }, @ovar{run-if-fail}, @ovar{run-if-pass})
18646 Execute a test by performing given shell @var{commands}. These commands
18647 should normally exit with @var{status}, while producing expected
18648 @var{stdout} and @var{stderr} contents. If @var{commands} exit with
18649 status 77, then the whole test group is skipped. Otherwise, if this test
18650 fails, run shell commands @var{run-if-fail} or, if this test passes, run shell
18651 commands @var{run-if-pass}.
18653 The @var{commands} @emph{must not} redirect the standard output, nor the
18656 If @var{status}, or @var{stdout}, or @var{stderr} is @samp{ignore}, then
18657 the corresponding value is not checked.
18659 The special value @samp{expout} for @var{stdout} means the expected
18660 output of the @var{commands} is the content of the file @file{expout}.
18661 If @var{stdout} is @samp{stdout}, then the standard output of the
18662 @var{commands} is available for further tests in the file @file{stdout}.
18663 Similarly for @var{stderr} with @samp{experr} and @samp{stderr}.
18667 @node testsuite Invocation
18668 @section Running @command{testsuite} Scripts
18669 @cindex @command{testsuite}
18671 Autotest test suites support the following arguments:
18676 Display the list of options and exit successfully.
18680 Display the version of the test suite and exit successfully.
18684 Remove all the files the test suite might have created and exit. Meant
18685 for @code{clean} Make targets.
18689 List all the tests (or only the selection), including their possible
18695 By default all tests are performed (or described with
18696 @option{--list}) in the default environment first silently, then
18697 verbosely, but the environment, set of tests, and verbosity level can be
18701 @item @var{variable}=@var{value}
18702 Set the environment @var{variable} to @var{value}. Use this rather
18703 than @samp{FOO=foo ./testsuite} as debugging scripts would then run in a
18704 different environment.
18706 @cindex @code{AUTOTEST_PATH}
18707 The variable @code{AUTOTEST_PATH} specifies the testing path to prepend
18708 to @env{PATH}. Relative directory names (not starting with
18709 @samp{/}) are considered to be relative to the top level of the
18710 package being built. All directories are made absolute, first
18711 starting from the top level @emph{build} tree, then from the
18712 @emph{source} tree. For instance @samp{./testsuite
18713 AUTOTEST_PATH=tests:bin} for a @file{/src/foo-1.0} source package built
18714 in @file{/tmp/foo} results in @samp{/tmp/foo/tests:/tmp/foo/bin} and
18715 then @samp{/src/foo-1.0/tests:/src/foo-1.0/bin} being prepended to
18719 @itemx @var{number}-@var{number}
18720 @itemx @var{number}-
18721 @itemx -@var{number}
18722 Add the corresponding test groups, with obvious semantics, to the
18725 @item --keywords=@var{keywords}
18726 @itemx -k @var{keywords}
18727 Add to the selection the test groups with title or keywords (arguments
18728 to @code{AT_SETUP} or @code{AT_KEYWORDS}) that match @emph{all} keywords
18729 of the comma separated list @var{keywords}, case-insensitively. Use
18730 @samp{!} immediately before the keyword to invert the selection for this
18731 keyword. By default, the keywords match whole words; enclose them in
18732 @samp{.*} to also match parts of words.
18734 For example, running
18737 @kbd{./testsuite -k 'autoupdate,.*FUNC.*'}
18741 selects all tests tagged @samp{autoupdate} @emph{and} with tags
18742 containing @samp{FUNC} (as in @samp{AC_CHECK_FUNC}, @samp{AC_FUNC_ALLOCA},
18746 @kbd{./testsuite -k '!autoupdate' -k '.*FUNC.*'}
18750 selects all tests not tagged @samp{autoupdate} @emph{or} with tags
18751 containing @samp{FUNC}.
18755 If any test fails, immediately abort testing. It implies
18756 @option{--debug}: post test group clean up, and top-level logging
18757 are inhibited. This option is meant for the full test
18758 suite, it is not really useful for generated debugging scripts.
18762 Force more verbosity in the detailed output of what is being done. This
18763 is the default for debugging scripts.
18767 Do not remove the files after a test group was performed ---but they are
18768 still removed @emph{before}, therefore using this option is sane when
18769 running several test groups. Create debugging scripts. Do not
18770 overwrite the top-level
18771 log (in order to preserve supposedly existing full log file). This is
18772 the default for debugging scripts, but it can also be useful to debug
18773 the testsuite itself.
18777 Trigger shell tracing of the test groups.
18781 @node Making testsuite Scripts
18782 @section Making @command{testsuite} Scripts
18784 For putting Autotest into movement, you need some configuration and
18785 makefile machinery. We recommend, at least if your package uses deep or
18786 shallow hierarchies, that you use @file{tests/} as the name of the
18787 directory holding all your tests and their makefile. Here is a
18788 check list of things to do.
18793 @cindex @file{package.m4}
18794 Make sure to create the file @file{package.m4}, which defines the
18795 identity of the package. It must define @code{AT_PACKAGE_STRING}, the
18796 full signature of the package, and @code{AT_PACKAGE_BUGREPORT}, the
18797 address to which bug reports should be sent. For sake of completeness,
18798 we suggest that you also define @code{AT_PACKAGE_NAME},
18799 @code{AT_PACKAGE_TARNAME}, and @code{AT_PACKAGE_VERSION}.
18800 @xref{Initializing configure}, for a description of these variables. We
18801 suggest the following makefile excerpt:
18804 $(srcdir)/package.m4: $(top_srcdir)/configure.ac
18806 echo '# Signature of the current package.'; \
18807 echo 'm4_define([AT_PACKAGE_NAME], [@@PACKAGE_NAME@@])'; \
18808 echo 'm4_define([AT_PACKAGE_TARNAME], [@@PACKAGE_TARNAME@@])'; \
18809 echo 'm4_define([AT_PACKAGE_VERSION], [@@PACKAGE_VERSION@@])'; \
18810 echo 'm4_define([AT_PACKAGE_STRING], [@@PACKAGE_STRING@@])'; \
18811 echo 'm4_define([AT_PACKAGE_BUGREPORT], [@@PACKAGE_BUGREPORT@@])'; \
18812 @} >'$(srcdir)/package.m4'
18816 Be sure to distribute @file{package.m4} and to put it into the source
18817 hierarchy: the test suite ought to be shipped!
18820 Invoke @code{AC_CONFIG_TESTDIR}.
18822 @defmac AC_CONFIG_TESTDIR (@var{directory}, @dvar{test-path, directory})
18823 @acindex{CONFIG_TESTDIR}
18824 An Autotest test suite is to be configured in @var{directory}. This
18825 macro requires the instantiation of @file{@var{directory}/atconfig} from
18826 @file{@var{directory}/atconfig.in}, and sets the default
18827 @code{AUTOTEST_PATH} to @var{test-path} (@pxref{testsuite Invocation}).
18831 Still within @file{configure.ac}, as appropriate, ensure that some
18832 @code{AC_CONFIG_FILES} command includes substitution for
18833 @file{tests/atlocal}.
18836 The @file{tests/Makefile.in} should be modified so the validation in
18837 your package is triggered by @samp{make check}. An example is provided
18841 With Automake, here is a minimal example about how to link @samp{make
18842 check} with a validation suite.
18845 EXTRA_DIST = testsuite.at $(TESTSUITE) atlocal.in
18846 TESTSUITE = $(srcdir)/testsuite
18848 check-local: atconfig atlocal $(TESTSUITE)
18849 $(SHELL) '$(TESTSUITE)' $(TESTSUITEFLAGS)
18851 installcheck-local: atconfig atlocal $(TESTSUITE)
18852 $(SHELL) '$(TESTSUITE)' AUTOTEST_PATH='$(bindir)' \
18856 test ! -f '$(TESTSUITE)' || \
18857 $(SHELL) '$(TESTSUITE)' --clean
18859 AUTOTEST = $(AUTOM4TE) --language=autotest
18860 $(TESTSUITE): $(srcdir)/testsuite.at
18861 $(AUTOTEST) -I '$(srcdir)' -o $@@.tmp $@@.at
18865 You might want to list explicitly the dependencies, i.e., the list of
18866 the files @file{testsuite.at} includes.
18868 With strict Autoconf, you might need to add lines inspired from the
18874 atconfig: $(top_builddir)/config.status
18875 cd $(top_builddir) && \
18876 $(SHELL) ./config.status $(subdir)/$@@
18878 atlocal: $(srcdir)/atlocal.in $(top_builddir)/config.status
18879 cd $(top_builddir) && \
18880 $(SHELL) ./config.status $(subdir)/$@@
18884 and manage to have @file{atconfig.in} and @code{$(EXTRA_DIST)}
18887 With all this in place, and if you have not initialized @samp{TESTSUITEFLAGS}
18888 within your makefile, you can fine-tune test suite execution with this variable,
18892 make check TESTSUITEFLAGS='-v -d -x 75 -k AC_PROG_CC CFLAGS=-g'
18897 @c =============================== Frequent Autoconf Questions, with answers
18900 @chapter Frequent Autoconf Questions, with answers
18902 Several questions about Autoconf come up occasionally. Here some of them
18906 * Distributing:: Distributing @command{configure} scripts
18907 * Why GNU M4:: Why not use the standard M4?
18908 * Bootstrapping:: Autoconf and @acronym{GNU} M4 require each other?
18909 * Why Not Imake:: Why @acronym{GNU} uses @command{configure} instead of Imake
18910 * Defining Directories:: Passing @code{datadir} to program
18911 * Autom4te Cache:: What is it? Can I remove it?
18912 * Present But Cannot Be Compiled:: Compiler and Preprocessor Disagree
18916 @section Distributing @command{configure} Scripts
18920 What are the restrictions on distributing @command{configure}
18921 scripts that Autoconf generates? How does that affect my
18922 programs that use them?
18925 There are no restrictions on how the configuration scripts that Autoconf
18926 produces may be distributed or used. In Autoconf version 1, they were
18927 covered by the @acronym{GNU} General Public License. We still encourage
18928 software authors to distribute their work under terms like those of the
18929 @acronym{GPL}, but doing so is not required to use Autoconf.
18931 Of the other files that might be used with @command{configure},
18932 @file{config.h.in} is under whatever copyright you use for your
18933 @file{configure.ac}. @file{config.sub} and @file{config.guess} have an
18934 exception to the @acronym{GPL} when they are used with an Autoconf-generated
18935 @command{configure} script, which permits you to distribute them under the
18936 same terms as the rest of your package. @file{install-sh} is from the X
18937 Consortium and is not copyrighted.
18940 @section Why Require @acronym{GNU} M4?
18943 Why does Autoconf require @acronym{GNU} M4?
18946 Many M4 implementations have hard-coded limitations on the size and
18947 number of macros that Autoconf exceeds. They also lack several
18948 builtin macros that it would be difficult to get along without in a
18949 sophisticated application like Autoconf, including:
18959 Autoconf requires version 1.4.5 or later of @acronym{GNU} M4.
18961 Since only software maintainers need to use Autoconf, and since @acronym{GNU}
18962 M4 is simple to configure and install, it seems reasonable to require
18963 @acronym{GNU} M4 to be installed also. Many maintainers of @acronym{GNU} and
18964 other free software already have most of the @acronym{GNU} utilities
18965 installed, since they prefer them.
18967 @node Bootstrapping
18968 @section How Can I Bootstrap?
18972 If Autoconf requires @acronym{GNU} M4 and @acronym{GNU} M4 has an Autoconf
18973 @command{configure} script, how do I bootstrap? It seems like a chicken
18977 This is a misunderstanding. Although @acronym{GNU} M4 does come with a
18978 @command{configure} script produced by Autoconf, Autoconf is not required
18979 in order to run the script and install @acronym{GNU} M4. Autoconf is only
18980 required if you want to change the M4 @command{configure} script, which few
18981 people have to do (mainly its maintainer).
18983 @node Why Not Imake
18984 @section Why Not Imake?
18988 Why not use Imake instead of @command{configure} scripts?
18991 Several people have written addressing this question, so I include
18992 adaptations of their explanations here.
18994 The following answer is based on one written by Richard Pixley:
18997 Autoconf generated scripts frequently work on machines that it has
18998 never been set up to handle before. That is, it does a good job of
18999 inferring a configuration for a new system. Imake cannot do this.
19001 Imake uses a common database of host specific data. For X11, this makes
19002 sense because the distribution is made as a collection of tools, by one
19003 central authority who has control over the database.
19005 @acronym{GNU} tools are not released this way. Each @acronym{GNU} tool has a
19006 maintainer; these maintainers are scattered across the world. Using a
19007 common database would be a maintenance nightmare. Autoconf may appear
19008 to be this kind of database, but in fact it is not. Instead of listing
19009 host dependencies, it lists program requirements.
19011 If you view the @acronym{GNU} suite as a collection of native tools, then the
19012 problems are similar. But the @acronym{GNU} development tools can be
19013 configured as cross tools in almost any host+target permutation. All of
19014 these configurations can be installed concurrently. They can even be
19015 configured to share host independent files across hosts. Imake doesn't
19016 address these issues.
19018 Imake templates are a form of standardization. The @acronym{GNU} coding
19019 standards address the same issues without necessarily imposing the same
19024 Here is some further explanation, written by Per Bothner:
19027 One of the advantages of Imake is that it easy to generate large
19028 makefiles using the @samp{#include} and macro mechanisms of @command{cpp}.
19029 However, @code{cpp} is not programmable: it has limited conditional
19030 facilities, and no looping. And @code{cpp} cannot inspect its
19033 All of these problems are solved by using @code{sh} instead of
19034 @code{cpp}. The shell is fully programmable, has macro substitution,
19035 can execute (or source) other shell scripts, and can inspect its
19040 Paul Eggert elaborates more:
19043 With Autoconf, installers need not assume that Imake itself is already
19044 installed and working well. This may not seem like much of an advantage
19045 to people who are accustomed to Imake. But on many hosts Imake is not
19046 installed or the default installation is not working well, and requiring
19047 Imake to install a package hinders the acceptance of that package on
19048 those hosts. For example, the Imake template and configuration files
19049 might not be installed properly on a host, or the Imake build procedure
19050 might wrongly assume that all source files are in one big directory
19051 tree, or the Imake configuration might assume one compiler whereas the
19052 package or the installer needs to use another, or there might be a
19053 version mismatch between the Imake expected by the package and the Imake
19054 supported by the host. These problems are much rarer with Autoconf,
19055 where each package comes with its own independent configuration
19058 Also, Imake often suffers from unexpected interactions between
19059 @command{make} and the installer's C preprocessor. The fundamental problem
19060 here is that the C preprocessor was designed to preprocess C programs,
19061 not makefiles. This is much less of a problem with Autoconf,
19062 which uses the general-purpose preprocessor M4, and where the
19063 package's author (rather than the installer) does the preprocessing in a
19068 Finally, Mark Eichin notes:
19071 Imake isn't all that extensible, either. In order to add new features to
19072 Imake, you need to provide your own project template, and duplicate most
19073 of the features of the existing one. This means that for a sophisticated
19074 project, using the vendor-provided Imake templates fails to provide any
19075 leverage---since they don't cover anything that your own project needs
19076 (unless it is an X11 program).
19078 On the other side, though:
19080 The one advantage that Imake has over @command{configure}:
19081 @file{Imakefile} files tend to be much shorter (likewise, less redundant)
19082 than @file{Makefile.in} files. There is a fix to this, however---at least
19083 for the Kerberos V5 tree, we've modified things to call in common
19084 @file{post.in} and @file{pre.in} makefile fragments for the
19085 entire tree. This means that a lot of common things don't have to be
19086 duplicated, even though they normally are in @command{configure} setups.
19090 @node Defining Directories
19091 @section How Do I @code{#define} Installation Directories?
19094 My program needs library files, installed in @code{datadir} and
19098 AC_DEFINE_UNQUOTED([DATADIR], [$datadir],
19099 [Define to the read-only architecture-independent
19107 #define DATADIR "$@{prefix@}/share"
19111 As already explained, this behavior is on purpose, mandated by the
19112 @acronym{GNU} Coding Standards, see @ref{Installation Directory
19113 Variables}. There are several means to achieve a similar goal:
19117 Do not use @code{AC_DEFINE} but use your makefile to pass the
19118 actual value of @code{datadir} via compilation flags.
19119 @xref{Installation Directory Variables}, for the details.
19122 This solution can be simplified when compiling a program: you may either
19123 extend the @code{CPPFLAGS}:
19126 CPPFLAGS = -DDATADIR='"$(datadir)"' @@CPPFLAGS@@
19130 or create a dedicated header file:
19133 DISTCLEANFILES = datadir.h
19134 datadir.h: Makefile
19135 echo '#define DATADIR "$(datadir)"' >$@@
19139 Use @code{AC_DEFINE} but have @command{configure} compute the literal
19140 value of @code{datadir} and others. Many people have wrapped macros to
19141 automate this task. For instance, the macro @code{AC_DEFINE_DIR} from
19142 the @uref{http://autoconf-archive.cryp.to/, Autoconf Macro
19145 This solution does not conform to the @acronym{GNU} Coding Standards.
19148 Note that all the previous solutions hard wire the absolute name of
19149 these directories in the executables, which is not a good property. You
19150 may try to compute the names relative to @code{prefix}, and try to
19151 find @code{prefix} at runtime, this way your package is relocatable.
19152 Some macros are already available to address this issue: see
19153 @code{adl_COMPUTE_RELATIVE_PATHS} and
19154 @code{adl_COMPUTE_STANDARD_RELATIVE_PATHS} on the
19155 @uref{http://autoconf-archive.cryp.to/,
19156 Autoconf Macro Archive}.
19160 @node Autom4te Cache
19161 @section What is @file{autom4te.cache}?
19164 What is this directory @file{autom4te.cache}? Can I safely remove it?
19167 In the @acronym{GNU} Build System, @file{configure.ac} plays a central
19168 role and is read by many tools: @command{autoconf} to create
19169 @file{configure}, @command{autoheader} to create @file{config.h.in},
19170 @command{automake} to create @file{Makefile.in}, @command{autoscan} to
19171 check the completeness of @file{configure.ac}, @command{autoreconf} to
19172 check the @acronym{GNU} Build System components that are used. To
19173 ``read @file{configure.ac}'' actually means to compile it with M4,
19174 which can be a long process for complex @file{configure.ac}.
19176 This is why all these tools, instead of running directly M4, invoke
19177 @command{autom4te} (@pxref{autom4te Invocation}) which, while answering to
19178 a specific demand, stores additional information in
19179 @file{autom4te.cache} for future runs. For instance, if you run
19180 @command{autoconf}, behind the scenes, @command{autom4te} also
19181 stores information for the other tools, so that when you invoke
19182 @command{autoheader} or @command{automake} etc., reprocessing
19183 @file{configure.ac} is not needed. The speed up is frequently of 30%,
19184 and is increasing with the size of @file{configure.ac}.
19186 But it is and remains being simply a cache: you can safely remove it.
19191 Can I permanently get rid of it?
19194 The creation of this cache can be disabled from
19195 @file{~/.autom4te.cfg}, see @ref{Customizing autom4te}, for more
19196 details. You should be aware that disabling the cache slows down the
19197 Autoconf test suite by 40%. The more @acronym{GNU} Build System
19198 components are used, the more the cache is useful; for instance
19199 running @samp{autoreconf -f} on the Core Utilities is twice slower without
19200 the cache @emph{although @option{--force} implies that the cache is
19201 not fully exploited}, and eight times slower than without
19205 @node Present But Cannot Be Compiled
19206 @section Header Present But Cannot Be Compiled
19208 The most important guideline to bear in mind when checking for
19209 features is to mimic as much as possible the intended use.
19210 Unfortunately, old versions of @code{AC_CHECK_HEADER} and
19211 @code{AC_CHECK_HEADERS} failed to follow this idea, and called
19212 the preprocessor, instead of the compiler, to check for headers. As a
19213 result, incompatibilities between headers went unnoticed during
19214 configuration, and maintainers finally had to deal with this issue
19217 As of Autoconf 2.56 both checks are performed, and @code{configure}
19218 complains loudly if the compiler and the preprocessor do not agree.
19219 For the time being the result used is that of the preprocessor, to give
19220 maintainers time to adjust their @file{configure.ac}, but in the
19221 future, only the compiler will be considered.
19223 Consider the following example:
19226 $ @kbd{cat number.h}
19227 typedef int number;
19229 const number pi = 3;
19230 $ @kbd{cat configure.ac}
19231 AC_INIT([Example], [1.0], [bug-example@@example.org])
19232 AC_CHECK_HEADERS([pi.h])
19233 $ @kbd{autoconf -Wall}
19234 $ @kbd{./configure}
19235 checking for gcc... gcc
19236 checking for C compiler default output file name... a.out
19237 checking whether the C compiler works... yes
19238 checking whether we are cross compiling... no
19239 checking for suffix of executables...
19240 checking for suffix of object files... o
19241 checking whether we are using the GNU C compiler... yes
19242 checking whether gcc accepts -g... yes
19243 checking for gcc option to accept ISO C89... none needed
19244 checking how to run the C preprocessor... gcc -E
19245 checking for grep that handles long lines and -e... grep
19246 checking for egrep... grep -E
19247 checking for ANSI C header files... yes
19248 checking for sys/types.h... yes
19249 checking for sys/stat.h... yes
19250 checking for stdlib.h... yes
19251 checking for string.h... yes
19252 checking for memory.h... yes
19253 checking for strings.h... yes
19254 checking for inttypes.h... yes
19255 checking for stdint.h... yes
19256 checking for unistd.h... yes
19257 checking pi.h usability... no
19258 checking pi.h presence... yes
19259 configure: WARNING: pi.h: present but cannot be compiled
19260 configure: WARNING: pi.h: check for missing prerequisite headers?
19261 configure: WARNING: pi.h: see the Autoconf documentation
19262 configure: WARNING: pi.h: section "Present But Cannot Be Compiled"
19263 configure: WARNING: pi.h: proceeding with the preprocessor's result
19264 configure: WARNING: pi.h: in the future, the compiler will take precedence
19265 configure: WARNING: ## -------------------------------------- ##
19266 configure: WARNING: ## Report this to bug-example@@example.org ##
19267 configure: WARNING: ## -------------------------------------- ##
19268 checking for pi.h... yes
19272 The proper way the handle this case is using the fourth argument
19273 (@pxref{Generic Headers}):
19276 $ @kbd{cat configure.ac}
19277 AC_INIT([Example], [1.0], [bug-example@@example.org])
19278 AC_CHECK_HEADERS([number.h pi.h], [], [],
19279 [[#ifdef HAVE_NUMBER_H
19280 # include <number.h>
19283 $ @kbd{autoconf -Wall}
19284 $ @kbd{./configure}
19285 checking for gcc... gcc
19286 checking for C compiler default output... a.out
19287 checking whether the C compiler works... yes
19288 checking whether we are cross compiling... no
19289 checking for suffix of executables...
19290 checking for suffix of object files... o
19291 checking whether we are using the GNU C compiler... yes
19292 checking whether gcc accepts -g... yes
19293 checking for gcc option to accept ANSI C... none needed
19294 checking for number.h... yes
19295 checking for pi.h... yes
19298 See @ref{Particular Headers}, for a list of headers with their
19301 @c ===================================================== History of Autoconf.
19304 @chapter History of Autoconf
19305 @cindex History of autoconf
19307 You may be wondering, Why was Autoconf originally written? How did it
19308 get into its present form? (Why does it look like gorilla spit?) If
19309 you're not wondering, then this chapter contains no information useful
19310 to you, and you might as well skip it. If you @emph{are} wondering,
19311 then let there be light@enddots{}
19314 * Genesis:: Prehistory and naming of @command{configure}
19315 * Exodus:: The plagues of M4 and Perl
19316 * Leviticus:: The priestly code of portability arrives
19317 * Numbers:: Growth and contributors
19318 * Deuteronomy:: Approaching the promises of easy configuration
19324 In June 1991 I was maintaining many of the @acronym{GNU} utilities for the
19325 Free Software Foundation. As they were ported to more platforms and
19326 more programs were added, the number of @option{-D} options that users
19327 had to select in the makefile (around 20) became burdensome.
19328 Especially for me---I had to test each new release on a bunch of
19329 different systems. So I wrote a little shell script to guess some of
19330 the correct settings for the fileutils package, and released it as part
19331 of fileutils 2.0. That @command{configure} script worked well enough that
19332 the next month I adapted it (by hand) to create similar @command{configure}
19333 scripts for several other @acronym{GNU} utilities packages. Brian Berliner
19334 also adapted one of my scripts for his @acronym{CVS} revision control system.
19336 Later that summer, I learned that Richard Stallman and Richard Pixley
19337 were developing similar scripts to use in the @acronym{GNU} compiler tools;
19338 so I adapted my @command{configure} scripts to support their evolving
19339 interface: using the file name @file{Makefile.in} as the templates;
19340 adding @samp{+srcdir}, the first option (of many); and creating
19341 @file{config.status} files.
19346 As I got feedback from users, I incorporated many improvements, using
19347 Emacs to search and replace, cut and paste, similar changes in each of
19348 the scripts. As I adapted more @acronym{GNU} utilities packages to use
19349 @command{configure} scripts, updating them all by hand became impractical.
19350 Rich Murphey, the maintainer of the @acronym{GNU} graphics utilities, sent me
19351 mail saying that the @command{configure} scripts were great, and asking if
19352 I had a tool for generating them that I could send him. No, I thought,
19353 but I should! So I started to work out how to generate them. And the
19354 journey from the slavery of hand-written @command{configure} scripts to the
19355 abundance and ease of Autoconf began.
19357 Cygnus @command{configure}, which was being developed at around that time,
19358 is table driven; it is meant to deal mainly with a discrete number of
19359 system types with a small number of mainly unguessable features (such as
19360 details of the object file format). The automatic configuration system
19361 that Brian Fox had developed for Bash takes a similar approach. For
19362 general use, it seems to me a hopeless cause to try to maintain an
19363 up-to-date database of which features each variant of each operating
19364 system has. It's easier and more reliable to check for most features on
19365 the fly---especially on hybrid systems that people have hacked on
19366 locally or that have patches from vendors installed.
19368 I considered using an architecture similar to that of Cygnus
19369 @command{configure}, where there is a single @command{configure} script that
19370 reads pieces of @file{configure.in} when run. But I didn't want to have
19371 to distribute all of the feature tests with every package, so I settled
19372 on having a different @command{configure} made from each
19373 @file{configure.in} by a preprocessor. That approach also offered more
19374 control and flexibility.
19376 I looked briefly into using the Metaconfig package, by Larry Wall,
19377 Harlan Stenn, and Raphael Manfredi, but I decided not to for several
19378 reasons. The @command{Configure} scripts it produces are interactive,
19379 which I find quite inconvenient; I didn't like the ways it checked for
19380 some features (such as library functions); I didn't know that it was
19381 still being maintained, and the @command{Configure} scripts I had
19382 seen didn't work on many modern systems (such as System V R4 and NeXT);
19383 it wasn't flexible in what it could do in response to a feature's
19384 presence or absence; I found it confusing to learn; and it was too big
19385 and complex for my needs (I didn't realize then how much Autoconf would
19386 eventually have to grow).
19388 I considered using Perl to generate my style of @command{configure}
19389 scripts, but decided that M4 was better suited to the job of simple
19390 textual substitutions: it gets in the way less, because output is
19391 implicit. Plus, everyone already has it. (Initially I didn't rely on
19392 the @acronym{GNU} extensions to M4.) Also, some of my friends at the
19393 University of Maryland had recently been putting M4 front ends on
19394 several programs, including @code{tvtwm}, and I was interested in trying
19395 out a new language.
19400 Since my @command{configure} scripts determine the system's capabilities
19401 automatically, with no interactive user intervention, I decided to call
19402 the program that generates them Autoconfig. But with a version number
19403 tacked on, that name would be too long for old Unix file systems,
19404 so I shortened it to Autoconf.
19406 In the fall of 1991 I called together a group of fellow questers after
19407 the Holy Grail of portability (er, that is, alpha testers) to give me
19408 feedback as I encapsulated pieces of my handwritten scripts in M4 macros
19409 and continued to add features and improve the techniques used in the
19410 checks. Prominent among the testers were Fran@,{c}ois Pinard, who came up
19411 with the idea of making an Autoconf shell script to run M4
19412 and check for unresolved macro calls; Richard Pixley, who suggested
19413 running the compiler instead of searching the file system to find
19414 include files and symbols, for more accurate results; Karl Berry, who
19415 got Autoconf to configure @TeX{} and added the macro index to the
19416 documentation; and Ian Lance Taylor, who added support for creating a C
19417 header file as an alternative to putting @option{-D} options in a
19418 makefile, so he could use Autoconf for his @acronym{UUCP} package.
19419 The alpha testers cheerfully adjusted their files again and again as the
19420 names and calling conventions of the Autoconf macros changed from
19421 release to release. They all contributed many specific checks, great
19422 ideas, and bug fixes.
19427 In July 1992, after months of alpha testing, I released Autoconf 1.0,
19428 and converted many @acronym{GNU} packages to use it. I was surprised by how
19429 positive the reaction to it was. More people started using it than I
19430 could keep track of, including people working on software that wasn't
19431 part of the @acronym{GNU} Project (such as TCL, FSP, and Kerberos V5).
19432 Autoconf continued to improve rapidly, as many people using the
19433 @command{configure} scripts reported problems they encountered.
19435 Autoconf turned out to be a good torture test for M4 implementations.
19436 Unix M4 started to dump core because of the length of the
19437 macros that Autoconf defined, and several bugs showed up in @acronym{GNU}
19438 M4 as well. Eventually, we realized that we needed to use some
19439 features that only @acronym{GNU} M4 has. 4.3@acronym{BSD} M4, in
19440 particular, has an impoverished set of builtin macros; the System V
19441 version is better, but still doesn't provide everything we need.
19443 More development occurred as people put Autoconf under more stresses
19444 (and to uses I hadn't anticipated). Karl Berry added checks for X11.
19445 david zuhn contributed C++ support. Fran@,{c}ois Pinard made it diagnose
19446 invalid arguments. Jim Blandy bravely coerced it into configuring
19447 @acronym{GNU} Emacs, laying the groundwork for several later improvements.
19448 Roland McGrath got it to configure the @acronym{GNU} C Library, wrote the
19449 @command{autoheader} script to automate the creation of C header file
19450 templates, and added a @option{--verbose} option to @command{configure}.
19451 Noah Friedman added the @option{--autoconf-dir} option and
19452 @code{AC_MACRODIR} environment variable. (He also coined the term
19453 @dfn{autoconfiscate} to mean ``adapt a software package to use
19454 Autoconf''.) Roland and Noah improved the quoting protection in
19455 @code{AC_DEFINE} and fixed many bugs, especially when I got sick of
19456 dealing with portability problems from February through June, 1993.
19459 @section Deuteronomy
19461 A long wish list for major features had accumulated, and the effect of
19462 several years of patching by various people had left some residual
19463 cruft. In April 1994, while working for Cygnus Support, I began a major
19464 revision of Autoconf. I added most of the features of the Cygnus
19465 @command{configure} that Autoconf had lacked, largely by adapting the
19466 relevant parts of Cygnus @command{configure} with the help of david zuhn
19467 and Ken Raeburn. These features include support for using
19468 @file{config.sub}, @file{config.guess}, @option{--host}, and
19469 @option{--target}; making links to files; and running @command{configure}
19470 scripts in subdirectories. Adding these features enabled Ken to convert
19471 @acronym{GNU} @code{as}, and Rob Savoye to convert Deja@acronym{GNU}, to using
19474 I added more features in response to other peoples' requests. Many
19475 people had asked for @command{configure} scripts to share the results of
19476 the checks between runs, because (particularly when configuring a large
19477 source tree, like Cygnus does) they were frustratingly slow. Mike
19478 Haertel suggested adding site-specific initialization scripts. People
19479 distributing software that had to unpack on MS-DOS asked for a way to
19480 override the @file{.in} extension on the file names, which produced file
19481 names like @file{config.h.in} containing two dots. Jim Avera did an
19482 extensive examination of the problems with quoting in @code{AC_DEFINE}
19483 and @code{AC_SUBST}; his insights led to significant improvements.
19484 Richard Stallman asked that compiler output be sent to @file{config.log}
19485 instead of @file{/dev/null}, to help people debug the Emacs
19486 @command{configure} script.
19488 I made some other changes because of my dissatisfaction with the quality
19489 of the program. I made the messages showing results of the checks less
19490 ambiguous, always printing a result. I regularized the names of the
19491 macros and cleaned up coding style inconsistencies. I added some
19492 auxiliary utilities that I had developed to help convert source code
19493 packages to use Autoconf. With the help of Fran@,{c}ois Pinard, I made
19494 the macros not interrupt each others' messages. (That feature revealed
19495 some performance bottlenecks in @acronym{GNU} M4, which he hastily
19496 corrected!) I reorganized the documentation around problems people want
19497 to solve. And I began a test suite, because experience had shown that
19498 Autoconf has a pronounced tendency to regress when we change it.
19500 Again, several alpha testers gave invaluable feedback, especially
19501 Fran@,{c}ois Pinard, Jim Meyering, Karl Berry, Rob Savoye, Ken Raeburn,
19504 Finally, version 2.0 was ready. And there was much rejoicing. (And I
19505 have free time again. I think. Yeah, right.)
19508 @c ========================================================== Appendices
19510 @node Copying This Manual
19511 @appendix Copying This Manual
19515 * GNU Free Documentation License:: License for copying this manual
19524 * Environment Variable Index:: Index of environment variables used
19525 * Output Variable Index:: Index of variables set in output files
19526 * Preprocessor Symbol Index:: Index of C preprocessor symbols defined
19527 * Autoconf Macro Index:: Index of Autoconf macros
19528 * M4 Macro Index:: Index of M4, M4sugar, and M4sh macros
19529 * Autotest Macro Index:: Index of Autotest macros
19530 * Program & Function Index:: Index of those with portability problems
19531 * Concept Index:: General index
19534 @node Environment Variable Index
19535 @appendixsec Environment Variable Index
19537 This is an alphabetical list of the environment variables that Autoconf
19542 @node Output Variable Index
19543 @appendixsec Output Variable Index
19545 This is an alphabetical list of the variables that Autoconf can
19546 substitute into files that it creates, typically one or more
19547 makefiles. @xref{Setting Output Variables}, for more information
19548 on how this is done.
19552 @node Preprocessor Symbol Index
19553 @appendixsec Preprocessor Symbol Index
19555 This is an alphabetical list of the C preprocessor symbols that the
19556 Autoconf macros define. To work with Autoconf, C source code needs to
19557 use these names in @code{#if} or @code{#ifdef} directives.
19561 @node Autoconf Macro Index
19562 @appendixsec Autoconf Macro Index
19564 This is an alphabetical list of the Autoconf macros.
19565 @ifset shortindexflag
19566 To make the list easier to use, the macros are listed without their
19567 preceding @samp{AC_}.
19572 @node M4 Macro Index
19573 @appendixsec M4 Macro Index
19575 This is an alphabetical list of the M4, M4sugar, and M4sh macros.
19576 @ifset shortindexflag
19577 To make the list easier to use, the macros are listed without their
19578 preceding @samp{m4_} or @samp{AS_}.
19583 @node Autotest Macro Index
19584 @appendixsec Autotest Macro Index
19586 This is an alphabetical list of the Autotest macros.
19587 @ifset shortindexflag
19588 To make the list easier to use, the macros are listed without their
19589 preceding @samp{AT_}.
19594 @node Program & Function Index
19595 @appendixsec Program and Function Index
19597 This is an alphabetical list of the programs and functions which
19598 portability is discussed in this document.
19602 @node Concept Index
19603 @appendixsec Concept Index
19605 This is an alphabetical list of the files, tools, and concepts
19606 introduced in this document.
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