1 \input texinfo @c -*- Texinfo -*-
7 @set RCSID $Id: make.texi,v 1.45 2006/04/01 06:36:40 psmith Exp $
9 @settitle GNU @code{make}
10 @setchapternewpage odd
11 @c Combine the variable and function indices:
13 @c Combine the program and concept indices:
15 @c FSF publishers: format makebook.texi instead of using this file directly.
16 @c ISBN provided by Lisa M. Opus Goldstein <opus@gnu.org>, 5 May 2004
17 @set ISBN 1-882114-83-5
21 This file documents the GNU @code{make} utility, which determines
22 automatically which pieces of a large program need to be recompiled,
23 and issues the commands to recompile them.
25 This is Edition @value{EDITION}, last updated @value{UPDATED},
26 of @cite{The GNU Make Manual}, for GNU @code{make} version @value{VERSION}.
28 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995,
29 1996, 1997, 1998, 1999, 2000, 2002, 2003, 2004, 2005, 2006
30 Free Software Foundation, Inc.
33 Permission is granted to copy, distribute and/or modify this document
34 under the terms of the GNU Free Documentation License, Version 1.2 or
35 any later version published by the Free Software Foundation; with no
36 Invariant Sections, with the Front-Cover Texts being ``A GNU Manual,''
37 and with the Back-Cover Texts as in (a) below. A copy of the
38 license is included in the section entitled ``GNU Free Documentation
41 (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
42 this GNU Manual, like GNU software. Copies published by the Free
43 Software Foundation raise funds for GNU development.''
49 @c ISPELL CHECK: done, 10 June 1993 --roland
50 @c ISPELL CHECK: done, 2000-06-25 --Martin Buchholz
53 @dircategory GNU Packages
55 * Make: (make). Remake files automatically.
59 @shorttitlepage GNU Make
63 @subtitle A Program for Directing Recompilation
64 @subtitle GNU @code{make} Version @value{VERSION}
65 @subtitle @value{UPDATED-MONTH}
66 @author Richard M. Stallman, Roland McGrath, Paul D. Smith
68 @vskip 0pt plus 1filll
71 Published by the Free Software Foundation @*
72 51 Franklin St. -- Fifth Floor @*
73 Boston, MA 02110-1301 USA @*
76 Cover art by Etienne Suvasa.
83 @node Top, Overview, (dir), (dir)
90 * Overview:: Overview of @code{make}.
91 * Introduction:: An introduction to @code{make}.
92 * Makefiles:: Makefiles tell @code{make} what to do.
93 * Rules:: Rules describe when a file must be remade.
94 * Commands:: Commands say how to remake a file.
95 * Using Variables:: You can use variables to avoid repetition.
96 * Conditionals:: Use or ignore parts of the makefile based
97 on the values of variables.
98 * Functions:: Many powerful ways to manipulate text.
99 * Invoking make: Running. How to invoke @code{make} on the command line.
100 * Implicit Rules:: Use implicit rules to treat many files alike,
101 based on their file names.
102 * Archives:: How @code{make} can update library archives.
103 * Features:: Features GNU @code{make} has over other @code{make}s.
104 * Missing:: What GNU @code{make} lacks from other @code{make}s.
105 * Makefile Conventions:: Conventions for writing makefiles for
107 * Quick Reference:: A quick reference for experienced users.
108 * Error Messages:: A list of common errors generated by @code{make}.
109 * Complex Makefile:: A real example of a straightforward,
110 but nontrivial, makefile.
112 * GNU Free Documentation License:: License for copying this manual
113 * Concept Index:: Index of Concepts
114 * Name Index:: Index of Functions, Variables, & Directives
117 --- The Detailed Node Listing ---
119 Overview of @code{make}
121 * Preparing:: Preparing and Running Make
122 * Reading:: On Reading this Text
123 * Bugs:: Problems and Bugs
125 An Introduction to Makefiles
127 * Rule Introduction:: What a rule looks like.
128 * Simple Makefile:: A Simple Makefile
129 * How Make Works:: How @code{make} Processes This Makefile
130 * Variables Simplify:: Variables Make Makefiles Simpler
131 * make Deduces:: Letting @code{make} Deduce the Commands
132 * Combine By Prerequisite:: Another Style of Makefile
133 * Cleanup:: Rules for Cleaning the Directory
137 * Makefile Contents:: What makefiles contain.
138 * Makefile Names:: How to name your makefile.
139 * Include:: How one makefile can use another makefile.
140 * MAKEFILES Variable:: The environment can specify extra makefiles.
141 * MAKEFILE_LIST Variable:: Discover which makefiles have been read.
142 * Special Variables:: Other special variables.
143 * Remaking Makefiles:: How makefiles get remade.
144 * Overriding Makefiles:: How to override part of one makefile
145 with another makefile.
146 * Reading Makefiles:: How makefiles are parsed.
147 * Secondary Expansion:: How and when secondary expansion is performed.
151 * Rule Example:: An example explained.
152 * Rule Syntax:: General syntax explained.
153 * Prerequisite Types:: There are two types of prerequisites.
154 * Wildcards:: Using wildcard characters such as `*'.
155 * Directory Search:: Searching other directories for source files.
156 * Phony Targets:: Using a target that is not a real file's name.
157 * Force Targets:: You can use a target without commands
158 or prerequisites to mark other targets
160 * Empty Targets:: When only the date matters and the
162 * Special Targets:: Targets with special built-in meanings.
163 * Multiple Targets:: When to make use of several targets in a rule.
164 * Multiple Rules:: How to use several rules with the same target.
165 * Static Pattern:: Static pattern rules apply to multiple targets
166 and can vary the prerequisites according to
168 * Double-Colon:: How to use a special kind of rule to allow
169 several independent rules for one target.
170 * Automatic Prerequisites:: How to automatically generate rules giving
171 prerequisites from source files themselves.
173 Using Wildcard Characters in File Names
175 * Wildcard Examples:: Several examples
176 * Wildcard Pitfall:: Problems to avoid.
177 * Wildcard Function:: How to cause wildcard expansion where
178 it does not normally take place.
180 Searching Directories for Prerequisites
182 * General Search:: Specifying a search path that applies
183 to every prerequisite.
184 * Selective Search:: Specifying a search path
185 for a specified class of names.
186 * Search Algorithm:: When and how search paths are applied.
187 * Commands/Search:: How to write shell commands that work together
189 * Implicit/Search:: How search paths affect implicit rules.
190 * Libraries/Search:: Directory search for link libraries.
194 * Static Usage:: The syntax of static pattern rules.
195 * Static versus Implicit:: When are they better than implicit rules?
197 Writing the Commands in Rules
199 * Command Syntax:: Command syntax features and pitfalls.
200 * Echoing:: How to control when commands are echoed.
201 * Execution:: How commands are executed.
202 * Parallel:: How commands can be executed in parallel.
203 * Errors:: What happens after a command execution error.
204 * Interrupts:: What happens when a command is interrupted.
205 * Recursion:: Invoking @code{make} from makefiles.
206 * Sequences:: Defining canned sequences of commands.
207 * Empty Commands:: Defining useful, do-nothing commands.
211 * Splitting Lines:: Breaking long command lines for readability.
212 * Variables in Commands:: Using @code{make} variables in commands.
216 * Choosing the Shell:: How @code{make} chooses the shell used
219 Recursive Use of @code{make}
221 * MAKE Variable:: The special effects of using @samp{$(MAKE)}.
222 * Variables/Recursion:: How to communicate variables to a sub-@code{make}.
223 * Options/Recursion:: How to communicate options to a sub-@code{make}.
224 * -w Option:: How the @samp{-w} or @samp{--print-directory} option
225 helps debug use of recursive @code{make} commands.
229 * Reference:: How to use the value of a variable.
230 * Flavors:: Variables come in two flavors.
231 * Advanced:: Advanced features for referencing a variable.
232 * Values:: All the ways variables get their values.
233 * Setting:: How to set a variable in the makefile.
234 * Appending:: How to append more text to the old value
236 * Override Directive:: How to set a variable in the makefile even if
237 the user has set it with a command argument.
238 * Defining:: An alternate way to set a variable
239 to a verbatim string.
240 * Environment:: Variable values can come from the environment.
241 * Target-specific:: Variable values can be defined on a per-target
243 * Pattern-specific:: Target-specific variable values can be applied
244 to a group of targets that match a pattern.
246 Advanced Features for Reference to Variables
248 * Substitution Refs:: Referencing a variable with
249 substitutions on the value.
250 * Computed Names:: Computing the name of the variable to refer to.
252 Conditional Parts of Makefiles
254 * Conditional Example:: Example of a conditional
255 * Conditional Syntax:: The syntax of conditionals.
256 * Testing Flags:: Conditionals that test flags.
258 Functions for Transforming Text
260 * Syntax of Functions:: How to write a function call.
261 * Text Functions:: General-purpose text manipulation functions.
262 * File Name Functions:: Functions for manipulating file names.
263 * Conditional Functions:: Functions that implement conditions.
264 * Foreach Function:: Repeat some text with controlled variation.
265 * Call Function:: Expand a user-defined function.
266 * Value Function:: Return the un-expanded value of a variable.
267 * Eval Function:: Evaluate the arguments as makefile syntax.
268 * Origin Function:: Find where a variable got its value.
269 * Flavor Function:: Find out the flavor of a variable.
270 * Shell Function:: Substitute the output of a shell command.
271 * Make Control Functions:: Functions that control how make runs.
273 How to Run @code{make}
275 * Makefile Arguments:: How to specify which makefile to use.
276 * Goals:: How to use goal arguments to specify which
277 parts of the makefile to use.
278 * Instead of Execution:: How to use mode flags to specify what
279 kind of thing to do with the commands
280 in the makefile other than simply
282 * Avoiding Compilation:: How to avoid recompiling certain files.
283 * Overriding:: How to override a variable to specify
284 an alternate compiler and other things.
285 * Testing:: How to proceed past some errors, to
287 * Options Summary:: Summary of Options
291 * Using Implicit:: How to use an existing implicit rule
292 to get the commands for updating a file.
293 * Catalogue of Rules:: A list of built-in implicit rules.
294 * Implicit Variables:: How to change what predefined rules do.
295 * Chained Rules:: How to use a chain of implicit rules.
296 * Pattern Rules:: How to define new implicit rules.
297 * Last Resort:: How to define commands for rules which
299 * Suffix Rules:: The old-fashioned style of implicit rule.
300 * Implicit Rule Search:: The precise algorithm for applying
303 Defining and Redefining Pattern Rules
305 * Pattern Intro:: An introduction to pattern rules.
306 * Pattern Examples:: Examples of pattern rules.
307 * Automatic Variables:: How to use automatic variables in the
308 commands of implicit rules.
309 * Pattern Match:: How patterns match.
310 * Match-Anything Rules:: Precautions you should take prior to
311 defining rules that can match any
312 target file whatever.
313 * Canceling Rules:: How to override or cancel built-in rules.
315 Using @code{make} to Update Archive Files
317 * Archive Members:: Archive members as targets.
318 * Archive Update:: The implicit rule for archive member targets.
319 * Archive Pitfalls:: Dangers to watch out for when using archives.
320 * Archive Suffix Rules:: You can write a special kind of suffix rule
321 for updating archives.
323 Implicit Rule for Archive Member Targets
325 * Archive Symbols:: How to update archive symbol directories.
330 @node Overview, Introduction, Top, Top
331 @comment node-name, next, previous, up
332 @chapter Overview of @code{make}
334 The @code{make} utility automatically determines which pieces of a large
335 program need to be recompiled, and issues commands to recompile them.
336 This manual describes GNU @code{make}, which was implemented by Richard
337 Stallman and Roland McGrath. Development since Version 3.76 has been
338 handled by Paul D. Smith.
340 GNU @code{make} conforms to section 6.2 of @cite{IEEE Standard
341 1003.2-1992} (POSIX.2).
343 @cindex IEEE Standard 1003.2
344 @cindex standards conformance
346 Our examples show C programs, since they are most common, but you can use
347 @code{make} with any programming language whose compiler can be run with a
348 shell command. Indeed, @code{make} is not limited to programs. You can
349 use it to describe any task where some files must be updated automatically
350 from others whenever the others change.
353 * Preparing:: Preparing and Running Make
354 * Reading:: On Reading this Text
355 * Bugs:: Problems and Bugs
358 @node Preparing, Reading, Overview, Overview
360 @heading Preparing and Running Make
363 To prepare to use @code{make}, you must write a file called
364 the @dfn{makefile} that describes the relationships among files
365 in your program and provides commands for updating each file.
366 In a program, typically, the executable file is updated from object
367 files, which are in turn made by compiling source files.@refill
369 Once a suitable makefile exists, each time you change some source files,
370 this simple shell command:
377 suffices to perform all necessary recompilations. The @code{make} program
378 uses the makefile data base and the last-modification times of the files to
379 decide which of the files need to be updated. For each of those files, it
380 issues the commands recorded in the data base.
382 You can provide command line arguments to @code{make} to control which
383 files should be recompiled, or how. @xref{Running, ,How to Run
386 @node Reading, Bugs, Preparing, Overview
387 @section How to Read This Manual
389 If you are new to @code{make}, or are looking for a general
390 introduction, read the first few sections of each chapter, skipping the
391 later sections. In each chapter, the first few sections contain
392 introductory or general information and the later sections contain
393 specialized or technical information.
395 The exception is the second chapter, @ref{Introduction, ,An
396 Introduction to Makefiles}, all of which is introductory.
399 The exception is @ref{Introduction, ,An Introduction to Makefiles},
400 all of which is introductory.
403 If you are familiar with other @code{make} programs, see @ref{Features,
404 ,Features of GNU @code{make}}, which lists the enhancements GNU
405 @code{make} has, and @ref{Missing, ,Incompatibilities and Missing
406 Features}, which explains the few things GNU @code{make} lacks that
409 For a quick summary, see @ref{Options Summary}, @ref{Quick Reference},
410 and @ref{Special Targets}.
412 @node Bugs, , Reading, Overview
413 @section Problems and Bugs
414 @cindex reporting bugs
415 @cindex bugs, reporting
416 @cindex problems and bugs, reporting
418 If you have problems with GNU @code{make} or think you've found a bug,
419 please report it to the developers; we cannot promise to do anything but
420 we might well want to fix it.
422 Before reporting a bug, make sure you've actually found a real bug.
423 Carefully reread the documentation and see if it really says you can do
424 what you're trying to do. If it's not clear whether you should be able
425 to do something or not, report that too; it's a bug in the
428 Before reporting a bug or trying to fix it yourself, try to isolate it
429 to the smallest possible makefile that reproduces the problem. Then
430 send us the makefile and the exact results @code{make} gave you,
431 including any error or warning messages. Please don't paraphrase
432 these messages: it's best to cut and paste them into your report.
433 When generating this small makefile, be sure to not use any non-free
434 or unusual tools in your commands: you can almost always emulate what
435 such a tool would do with simple shell commands. Finally, be sure to
436 explain what you expected to occur; this will help us decide whether
437 the problem was really in the documentation.
439 Once you have a precise problem you can report it in one of two ways.
440 Either send electronic mail to:
447 or use our Web-based project management tool, at:
450 http://savannah.gnu.org/projects/make/
454 In addition to the information above, please be careful to include the
455 version number of @code{make} you are using. You can get this
456 information with the command @samp{make --version}. Be sure also to
457 include the type of machine and operating system you are using. One
458 way to obtain this information is by looking at the final lines of
459 output from the command @samp{make --help}.
461 @node Introduction, Makefiles, Overview, Top
462 @comment node-name, next, previous, up
463 @chapter An Introduction to Makefiles
465 You need a file called a @dfn{makefile} to tell @code{make} what to do.
466 Most often, the makefile tells @code{make} how to compile and link a
470 In this chapter, we will discuss a simple makefile that describes how to
471 compile and link a text editor which consists of eight C source files
472 and three header files. The makefile can also tell @code{make} how to
473 run miscellaneous commands when explicitly asked (for example, to remove
474 certain files as a clean-up operation). To see a more complex example
475 of a makefile, see @ref{Complex Makefile}.
477 When @code{make} recompiles the editor, each changed C source file
478 must be recompiled. If a header file has changed, each C source file
479 that includes the header file must be recompiled to be safe. Each
480 compilation produces an object file corresponding to the source file.
481 Finally, if any source file has been recompiled, all the object files,
482 whether newly made or saved from previous compilations, must be linked
483 together to produce the new executable editor.
484 @cindex recompilation
488 * Rule Introduction:: What a rule looks like.
489 * Simple Makefile:: A Simple Makefile
490 * How Make Works:: How @code{make} Processes This Makefile
491 * Variables Simplify:: Variables Make Makefiles Simpler
492 * make Deduces:: Letting @code{make} Deduce the Commands
493 * Combine By Prerequisite:: Another Style of Makefile
494 * Cleanup:: Rules for Cleaning the Directory
497 @node Rule Introduction, Simple Makefile, Introduction, Introduction
498 @comment node-name, next, previous, up
499 @section What a Rule Looks Like
500 @cindex rule, introduction to
501 @cindex makefile rule parts
502 @cindex parts of makefile rule
504 A simple makefile consists of ``rules'' with the following shape:
506 @cindex targets, introduction to
507 @cindex prerequisites, introduction to
508 @cindex commands, introduction to
511 @var{target} @dots{} : @var{prerequisites} @dots{}
518 A @dfn{target} is usually the name of a file that is generated by a
519 program; examples of targets are executable or object files. A target
520 can also be the name of an action to carry out, such as @samp{clean}
521 (@pxref{Phony Targets}).
523 A @dfn{prerequisite} is a file that is used as input to create the
524 target. A target often depends on several files.
526 @cindex tabs in rules
527 A @dfn{command} is an action that @code{make} carries out.
528 A rule may have more than one command, each on its own line.
529 @strong{Please note:} you need to put a tab character at the beginning of
530 every command line! This is an obscurity that catches the unwary.
532 Usually a command is in a rule with prerequisites and serves to create a
533 target file if any of the prerequisites change. However, the rule that
534 specifies commands for the target need not have prerequisites. For
535 example, the rule containing the delete command associated with the
536 target @samp{clean} does not have prerequisites.
538 A @dfn{rule}, then, explains how and when to remake certain files
539 which are the targets of the particular rule. @code{make} carries out
540 the commands on the prerequisites to create or update the target. A
541 rule can also explain how and when to carry out an action.
542 @xref{Rules, , Writing Rules}.
544 A makefile may contain other text besides rules, but a simple makefile
545 need only contain rules. Rules may look somewhat more complicated
546 than shown in this template, but all fit the pattern more or less.
548 @node Simple Makefile, How Make Works, Rule Introduction, Introduction
549 @section A Simple Makefile
550 @cindex simple makefile
551 @cindex makefile, simple
553 Here is a straightforward makefile that describes the way an
554 executable file called @code{edit} depends on eight object files
555 which, in turn, depend on eight C source and three header files.
557 In this example, all the C files include @file{defs.h}, but only those
558 defining editing commands include @file{command.h}, and only low
559 level files that change the editor buffer include @file{buffer.h}.
563 edit : main.o kbd.o command.o display.o \
564 insert.o search.o files.o utils.o
565 cc -o edit main.o kbd.o command.o display.o \
566 insert.o search.o files.o utils.o
568 main.o : main.c defs.h
570 kbd.o : kbd.c defs.h command.h
572 command.o : command.c defs.h command.h
574 display.o : display.c defs.h buffer.h
576 insert.o : insert.c defs.h buffer.h
578 search.o : search.c defs.h buffer.h
580 files.o : files.c defs.h buffer.h command.h
582 utils.o : utils.c defs.h
585 rm edit main.o kbd.o command.o display.o \
586 insert.o search.o files.o utils.o
591 We split each long line into two lines using backslash-newline; this is
592 like using one long line, but is easier to read.
593 @cindex continuation lines
594 @cindex @code{\} (backslash), for continuation lines
595 @cindex backslash (@code{\}), for continuation lines
596 @cindex quoting newline, in makefile
597 @cindex newline, quoting, in makefile
599 To use this makefile to create the executable file called @file{edit},
606 To use this makefile to delete the executable file and all the object
607 files from the directory, type:
613 In the example makefile, the targets include the executable file
614 @samp{edit}, and the object files @samp{main.o} and @samp{kbd.o}. The
615 prerequisites are files such as @samp{main.c} and @samp{defs.h}.
616 In fact, each @samp{.o} file is both a target and a prerequisite.
617 Commands include @w{@samp{cc -c main.c}} and @w{@samp{cc -c kbd.c}}.
619 When a target is a file, it needs to be recompiled or relinked if any
620 of its prerequisites change. In addition, any prerequisites that are
621 themselves automatically generated should be updated first. In this
622 example, @file{edit} depends on each of the eight object files; the
623 object file @file{main.o} depends on the source file @file{main.c} and
624 on the header file @file{defs.h}.
626 A shell command follows each line that contains a target and
627 prerequisites. These shell commands say how to update the target file.
628 A tab character must come at the beginning of every command line to
629 distinguish command lines from other lines in the makefile. (Bear in
630 mind that @code{make} does not know anything about how the commands
631 work. It is up to you to supply commands that will update the target
632 file properly. All @code{make} does is execute the commands in the rule
633 you have specified when the target file needs to be updated.)
634 @cindex shell command
636 The target @samp{clean} is not a file, but merely the name of an
639 do not want to carry out the actions in this rule, @samp{clean} is not a prerequisite of any other rule.
640 Consequently, @code{make} never does anything with it unless you tell
641 it specifically. Note that this rule not only is not a prerequisite, it
642 also does not have any prerequisites, so the only purpose of the rule
643 is to run the specified commands. Targets that do not refer to files
644 but are just actions are called @dfn{phony targets}. @xref{Phony
645 Targets}, for information about this kind of target. @xref{Errors, ,
646 Errors in Commands}, to see how to cause @code{make} to ignore errors
647 from @code{rm} or any other command.
648 @cindex @code{clean} target
649 @cindex @code{rm} (shell command)
651 @node How Make Works, Variables Simplify, Simple Makefile, Introduction
652 @comment node-name, next, previous, up
653 @section How @code{make} Processes a Makefile
654 @cindex processing a makefile
655 @cindex makefile, how @code{make} processes
657 By default, @code{make} starts with the first target (not targets whose
658 names start with @samp{.}). This is called the @dfn{default goal}.
659 (@dfn{Goals} are the targets that @code{make} strives ultimately to
660 update. You can override this behavior using the command line
661 (@pxref{Goals, , Arguments to Specify the Goals}) or with the
662 @code{.DEFAULT_GOAL} special variable (@pxref{Special Variables, ,
663 Other Special Variables}).
665 @cindex goal, default
668 In the simple example of the previous section, the default goal is to
669 update the executable program @file{edit}; therefore, we put that rule
672 Thus, when you give the command:
679 @code{make} reads the makefile in the current directory and begins by
680 processing the first rule. In the example, this rule is for relinking
681 @file{edit}; but before @code{make} can fully process this rule, it
682 must process the rules for the files that @file{edit} depends on,
683 which in this case are the object files. Each of these files is
684 processed according to its own rule. These rules say to update each
685 @samp{.o} file by compiling its source file. The recompilation must
686 be done if the source file, or any of the header files named as
687 prerequisites, is more recent than the object file, or if the object
690 The other rules are processed because their targets appear as
691 prerequisites of the goal. If some other rule is not depended on by the
692 goal (or anything it depends on, etc.), that rule is not processed,
693 unless you tell @code{make} to do so (with a command such as
694 @w{@code{make clean}}).
696 Before recompiling an object file, @code{make} considers updating its
697 prerequisites, the source file and header files. This makefile does not
698 specify anything to be done for them---the @samp{.c} and @samp{.h} files
699 are not the targets of any rules---so @code{make} does nothing for these
700 files. But @code{make} would update automatically generated C programs,
701 such as those made by Bison or Yacc, by their own rules at this time.
703 After recompiling whichever object files need it, @code{make} decides
704 whether to relink @file{edit}. This must be done if the file
705 @file{edit} does not exist, or if any of the object files are newer than
706 it. If an object file was just recompiled, it is now newer than
707 @file{edit}, so @file{edit} is relinked.
710 Thus, if we change the file @file{insert.c} and run @code{make},
711 @code{make} will compile that file to update @file{insert.o}, and then
712 link @file{edit}. If we change the file @file{command.h} and run
713 @code{make}, @code{make} will recompile the object files @file{kbd.o},
714 @file{command.o} and @file{files.o} and then link the file @file{edit}.
716 @node Variables Simplify, make Deduces, How Make Works, Introduction
717 @section Variables Make Makefiles Simpler
719 @cindex simplifying with variables
721 In our example, we had to list all the object files twice in the rule for
722 @file{edit} (repeated here):
726 edit : main.o kbd.o command.o display.o \
727 insert.o search.o files.o utils.o
728 cc -o edit main.o kbd.o command.o display.o \
729 insert.o search.o files.o utils.o
733 @cindex @code{objects}
734 Such duplication is error-prone; if a new object file is added to the
735 system, we might add it to one list and forget the other. We can eliminate
736 the risk and simplify the makefile by using a variable. @dfn{Variables}
737 allow a text string to be defined once and substituted in multiple places
738 later (@pxref{Using Variables, ,How to Use Variables}).
740 @cindex @code{OBJECTS}
745 It is standard practice for every makefile to have a variable named
746 @code{objects}, @code{OBJECTS}, @code{objs}, @code{OBJS}, @code{obj},
747 or @code{OBJ} which is a list of all object file names. We would
748 define such a variable @code{objects} with a line like this in the
753 objects = main.o kbd.o command.o display.o \
754 insert.o search.o files.o utils.o
759 Then, each place we want to put a list of the object file names, we can
760 substitute the variable's value by writing @samp{$(objects)}
761 (@pxref{Using Variables, ,How to Use Variables}).
763 Here is how the complete simple makefile looks when you use a variable
764 for the object files:
768 objects = main.o kbd.o command.o display.o \
769 insert.o search.o files.o utils.o
772 cc -o edit $(objects)
773 main.o : main.c defs.h
775 kbd.o : kbd.c defs.h command.h
777 command.o : command.c defs.h command.h
779 display.o : display.c defs.h buffer.h
781 insert.o : insert.c defs.h buffer.h
783 search.o : search.c defs.h buffer.h
785 files.o : files.c defs.h buffer.h command.h
787 utils.o : utils.c defs.h
794 @node make Deduces, Combine By Prerequisite, Variables Simplify, Introduction
795 @section Letting @code{make} Deduce the Commands
796 @cindex deducing commands (implicit rules)
797 @cindex implicit rule, introduction to
798 @cindex rule, implicit, introduction to
800 It is not necessary to spell out the commands for compiling the individual
801 C source files, because @code{make} can figure them out: it has an
802 @dfn{implicit rule} for updating a @samp{.o} file from a correspondingly
803 named @samp{.c} file using a @samp{cc -c} command. For example, it will
804 use the command @samp{cc -c main.c -o main.o} to compile @file{main.c} into
805 @file{main.o}. We can therefore omit the commands from the rules for the
806 object files. @xref{Implicit Rules, ,Using Implicit Rules}.@refill
808 When a @samp{.c} file is used automatically in this way, it is also
809 automatically added to the list of prerequisites. We can therefore omit
810 the @samp{.c} files from the prerequisites, provided we omit the commands.
812 Here is the entire example, with both of these changes, and a variable
813 @code{objects} as suggested above:
817 objects = main.o kbd.o command.o display.o \
818 insert.o search.o files.o utils.o
821 cc -o edit $(objects)
824 kbd.o : defs.h command.h
825 command.o : defs.h command.h
826 display.o : defs.h buffer.h
827 insert.o : defs.h buffer.h
828 search.o : defs.h buffer.h
829 files.o : defs.h buffer.h command.h
839 This is how we would write the makefile in actual practice. (The
840 complications associated with @samp{clean} are described elsewhere.
841 See @ref{Phony Targets}, and @ref{Errors, ,Errors in Commands}.)
843 Because implicit rules are so convenient, they are important. You
844 will see them used frequently.@refill
846 @node Combine By Prerequisite, Cleanup, make Deduces, Introduction
847 @section Another Style of Makefile
848 @cindex combining rules by prerequisite
850 When the objects of a makefile are created only by implicit rules, an
851 alternative style of makefile is possible. In this style of makefile,
852 you group entries by their prerequisites instead of by their targets.
853 Here is what one looks like:
857 objects = main.o kbd.o command.o display.o \
858 insert.o search.o files.o utils.o
861 cc -o edit $(objects)
864 kbd.o command.o files.o : command.h
865 display.o insert.o search.o files.o : buffer.h
870 Here @file{defs.h} is given as a prerequisite of all the object files;
871 @file{command.h} and @file{buffer.h} are prerequisites of the specific
872 object files listed for them.
874 Whether this is better is a matter of taste: it is more compact, but some
875 people dislike it because they find it clearer to put all the information
876 about each target in one place.
878 @node Cleanup, , Combine By Prerequisite, Introduction
879 @section Rules for Cleaning the Directory
881 @cindex removing, to clean up
883 Compiling a program is not the only thing you might want to write rules
884 for. Makefiles commonly tell how to do a few other things besides
885 compiling a program: for example, how to delete all the object files
886 and executables so that the directory is @samp{clean}.
888 @cindex @code{clean} target
890 could write a @code{make} rule for cleaning our example editor:
899 In practice, we might want to write the rule in a somewhat more
900 complicated manner to handle unanticipated situations. We would do this:
911 This prevents @code{make} from getting confused by an actual file
912 called @file{clean} and causes it to continue in spite of errors from
913 @code{rm}. (See @ref{Phony Targets}, and @ref{Errors, ,Errors in
917 A rule such as this should not be placed at the beginning of the
918 makefile, because we do not want it to run by default! Thus, in the
919 example makefile, we want the rule for @code{edit}, which recompiles
920 the editor, to remain the default goal.
922 Since @code{clean} is not a prerequisite of @code{edit}, this rule will not
923 run at all if we give the command @samp{make} with no arguments. In
924 order to make the rule run, we have to type @samp{make clean}.
925 @xref{Running, ,How to Run @code{make}}.
927 @node Makefiles, Rules, Introduction, Top
928 @chapter Writing Makefiles
930 @cindex makefile, how to write
931 The information that tells @code{make} how to recompile a system comes from
932 reading a data base called the @dfn{makefile}.
935 * Makefile Contents:: What makefiles contain.
936 * Makefile Names:: How to name your makefile.
937 * Include:: How one makefile can use another makefile.
938 * MAKEFILES Variable:: The environment can specify extra makefiles.
939 * MAKEFILE_LIST Variable:: Discover which makefiles have been read.
940 * Special Variables:: Other special variables.
941 * Remaking Makefiles:: How makefiles get remade.
942 * Overriding Makefiles:: How to override part of one makefile
943 with another makefile.
944 * Reading Makefiles:: How makefiles are parsed.
945 * Secondary Expansion:: How and when secondary expansion is performed.
948 @node Makefile Contents, Makefile Names, Makefiles, Makefiles
949 @section What Makefiles Contain
951 Makefiles contain five kinds of things: @dfn{explicit rules},
952 @dfn{implicit rules}, @dfn{variable definitions}, @dfn{directives},
953 and @dfn{comments}. Rules, variables, and directives are described at
954 length in later chapters.@refill
957 @cindex rule, explicit, definition of
958 @cindex explicit rule, definition of
960 An @dfn{explicit rule} says when and how to remake one or more files,
961 called the rule's @dfn{targets}. It lists the other files that the
962 targets depend on, called the @dfn{prerequisites} of the target, and
963 may also give commands to use to create or update the targets.
964 @xref{Rules, ,Writing Rules}.
966 @cindex rule, implicit, definition of
967 @cindex implicit rule, definition of
969 An @dfn{implicit rule} says when and how to remake a class of files
970 based on their names. It describes how a target may depend on a file
971 with a name similar to the target and gives commands to create or
972 update such a target. @xref{Implicit Rules, ,Using Implicit Rules}.
974 @cindex variable definition
976 A @dfn{variable definition} is a line that specifies a text string
977 value for a variable that can be substituted into the text later. The
978 simple makefile example shows a variable definition for @code{objects}
979 as a list of all object files (@pxref{Variables Simplify, , Variables
980 Make Makefiles Simpler}).
984 A @dfn{directive} is a command for @code{make} to do something special while
985 reading the makefile. These include:
989 Reading another makefile (@pxref{Include, ,Including Other Makefiles}).
992 Deciding (based on the values of variables) whether to use or
993 ignore a part of the makefile (@pxref{Conditionals, ,Conditional Parts of Makefiles}).
996 Defining a variable from a verbatim string containing multiple lines
997 (@pxref{Defining, ,Defining Variables Verbatim}).
1000 @cindex comments, in makefile
1001 @cindex @code{#} (comments), in makefile
1003 @samp{#} in a line of a makefile starts a @dfn{comment}. It and the
1004 rest of the line are ignored, except that a trailing backslash not
1005 escaped by another backslash will continue the comment across multiple
1006 lines. A line containing just a comment (with perhaps spaces before
1007 it) is effectively blank, and is ignored. If you want a literal
1008 @code{#}, escape it with a backslash (e.g., @code{\#}). Comments may
1009 appear on any line in the makefile, although they are treated
1010 specially in certain situations.
1012 Within a command script (if the line begins with a TAB character) the
1013 entire line is passed to the shell, just as with any other line that
1014 begins with a TAB. The shell decides how to interpret the text:
1015 whether or not this is a comment is up to the shell.
1017 Within a @code{define} directive, comments are not ignored during the
1018 definition of the variable, but rather kept intact in the value of the
1019 variable. When the variable is expanded they will either be treated
1020 as @code{make} comments or as command script text, depending on the
1021 context in which the variable is evaluated.
1024 @node Makefile Names, Include, Makefile Contents, Makefiles
1025 @section What Name to Give Your Makefile
1026 @cindex makefile name
1027 @cindex name of makefile
1028 @cindex default makefile name
1029 @cindex file name of makefile
1031 @c following paragraph rewritten to avoid overfull hbox
1032 By default, when @code{make} looks for the makefile, it tries the
1033 following names, in order: @file{GNUmakefile}, @file{makefile}
1034 and @file{Makefile}.@refill
1039 @cindex @code{README}
1040 Normally you should call your makefile either @file{makefile} or
1041 @file{Makefile}. (We recommend @file{Makefile} because it appears
1042 prominently near the beginning of a directory listing, right near other
1043 important files such as @file{README}.) The first name checked,
1044 @file{GNUmakefile}, is not recommended for most makefiles. You should
1045 use this name if you have a makefile that is specific to GNU
1046 @code{make}, and will not be understood by other versions of
1047 @code{make}. Other @code{make} programs look for @file{makefile} and
1048 @file{Makefile}, but not @file{GNUmakefile}.
1050 If @code{make} finds none of these names, it does not use any makefile.
1051 Then you must specify a goal with a command argument, and @code{make}
1052 will attempt to figure out how to remake it using only its built-in
1053 implicit rules. @xref{Implicit Rules, ,Using Implicit Rules}.
1056 @cindex @code{--file}
1057 @cindex @code{--makefile}
1058 If you want to use a nonstandard name for your makefile, you can specify
1059 the makefile name with the @samp{-f} or @samp{--file} option. The
1060 arguments @w{@samp{-f @var{name}}} or @w{@samp{--file=@var{name}}} tell
1061 @code{make} to read the file @var{name} as the makefile. If you use
1062 more than one @samp{-f} or @samp{--file} option, you can specify several
1063 makefiles. All the makefiles are effectively concatenated in the order
1064 specified. The default makefile names @file{GNUmakefile},
1065 @file{makefile} and @file{Makefile} are not checked automatically if you
1066 specify @samp{-f} or @samp{--file}.@refill
1067 @cindex specifying makefile name
1068 @cindex makefile name, how to specify
1069 @cindex name of makefile, how to specify
1070 @cindex file name of makefile, how to specify
1072 @node Include, MAKEFILES Variable, Makefile Names, Makefiles
1073 @section Including Other Makefiles
1074 @cindex including other makefiles
1075 @cindex makefile, including
1078 The @code{include} directive tells @code{make} to suspend reading the
1079 current makefile and read one or more other makefiles before continuing.
1080 The directive is a line in the makefile that looks like this:
1083 include @var{filenames}@dots{}
1087 @var{filenames} can contain shell file name patterns. If
1088 @var{filenames} is empty, nothing is included and no error is printed.
1089 @cindex shell file name pattern (in @code{include})
1090 @cindex shell wildcards (in @code{include})
1091 @cindex wildcard, in @code{include}
1093 Extra spaces are allowed and ignored at the beginning of the line, but
1094 a tab is not allowed. (If the line begins with a tab, it will be
1095 considered a command line.) Whitespace is required between
1096 @code{include} and the file names, and between file names; extra
1097 whitespace is ignored there and at the end of the directive. A
1098 comment starting with @samp{#} is allowed at the end of the line. If
1099 the file names contain any variable or function references, they are
1100 expanded. @xref{Using Variables, ,How to Use Variables}.
1102 For example, if you have three @file{.mk} files, @file{a.mk},
1103 @file{b.mk}, and @file{c.mk}, and @code{$(bar)} expands to
1104 @code{bish bash}, then the following expression
1107 include foo *.mk $(bar)
1113 include foo a.mk b.mk c.mk bish bash
1116 When @code{make} processes an @code{include} directive, it suspends
1117 reading of the containing makefile and reads from each listed file in
1118 turn. When that is finished, @code{make} resumes reading the
1119 makefile in which the directive appears.
1121 One occasion for using @code{include} directives is when several programs,
1122 handled by individual makefiles in various directories, need to use a
1123 common set of variable definitions
1124 (@pxref{Setting, ,Setting Variables}) or pattern rules
1125 (@pxref{Pattern Rules, ,Defining and Redefining Pattern Rules}).
1127 Another such occasion is when you want to generate prerequisites from
1128 source files automatically; the prerequisites can be put in a file that
1129 is included by the main makefile. This practice is generally cleaner
1130 than that of somehow appending the prerequisites to the end of the main
1131 makefile as has been traditionally done with other versions of
1132 @code{make}. @xref{Automatic Prerequisites}.
1133 @cindex prerequisites, automatic generation
1134 @cindex automatic generation of prerequisites
1135 @cindex generating prerequisites automatically
1138 @cindex @code{--include-dir}
1139 @cindex included makefiles, default directories
1140 @cindex default directories for included makefiles
1141 @findex /usr/gnu/include
1142 @findex /usr/local/include
1143 @findex /usr/include
1144 If the specified name does not start with a slash, and the file is not
1145 found in the current directory, several other directories are searched.
1146 First, any directories you have specified with the @samp{-I} or
1147 @samp{--include-dir} option are searched
1148 (@pxref{Options Summary, ,Summary of Options}).
1149 Then the following directories (if they exist)
1150 are searched, in this order:
1151 @file{@var{prefix}/include} (normally @file{/usr/local/include}
1152 @footnote{GNU Make compiled for MS-DOS and MS-Windows behaves as if
1153 @var{prefix} has been defined to be the root of the DJGPP tree
1155 @file{/usr/gnu/include},
1156 @file{/usr/local/include}, @file{/usr/include}.
1158 If an included makefile cannot be found in any of these directories, a
1159 warning message is generated, but it is not an immediately fatal error;
1160 processing of the makefile containing the @code{include} continues.
1161 Once it has finished reading makefiles, @code{make} will try to remake
1162 any that are out of date or don't exist.
1163 @xref{Remaking Makefiles, ,How Makefiles Are Remade}.
1164 Only after it has tried to find a way to remake a makefile and failed,
1165 will @code{make} diagnose the missing makefile as a fatal error.
1167 If you want @code{make} to simply ignore a makefile which does not exist
1168 and cannot be remade, with no error message, use the @w{@code{-include}}
1169 directive instead of @code{include}, like this:
1172 -include @var{filenames}@dots{}
1175 This acts like @code{include} in every way except that there is no
1176 error (not even a warning) if any of the @var{filenames} do not exist.
1177 For compatibility with some other @code{make} implementations,
1178 @code{sinclude} is another name for @w{@code{-include}}.
1180 @node MAKEFILES Variable, MAKEFILE_LIST Variable, Include, Makefiles
1181 @section The Variable @code{MAKEFILES}
1182 @cindex makefile, and @code{MAKEFILES} variable
1183 @cindex including (@code{MAKEFILES} variable)
1186 If the environment variable @code{MAKEFILES} is defined, @code{make}
1187 considers its value as a list of names (separated by whitespace) of
1188 additional makefiles to be read before the others. This works much like
1189 the @code{include} directive: various directories are searched for those
1190 files (@pxref{Include, ,Including Other Makefiles}). In addition, the
1191 default goal is never taken from one of these makefiles and it is not an
1192 error if the files listed in @code{MAKEFILES} are not found.@refill
1194 @cindex recursion, and @code{MAKEFILES} variable
1195 The main use of @code{MAKEFILES} is in communication between recursive
1196 invocations of @code{make} (@pxref{Recursion, ,Recursive Use of
1197 @code{make}}). It usually is not desirable to set the environment
1198 variable before a top-level invocation of @code{make}, because it is
1199 usually better not to mess with a makefile from outside. However, if
1200 you are running @code{make} without a specific makefile, a makefile in
1201 @code{MAKEFILES} can do useful things to help the built-in implicit
1202 rules work better, such as defining search paths (@pxref{Directory Search}).
1204 Some users are tempted to set @code{MAKEFILES} in the environment
1205 automatically on login, and program makefiles to expect this to be done.
1206 This is a very bad idea, because such makefiles will fail to work if run by
1207 anyone else. It is much better to write explicit @code{include} directives
1208 in the makefiles. @xref{Include, , Including Other Makefiles}.
1210 @node MAKEFILE_LIST Variable, Special Variables, MAKEFILES Variable, Makefiles
1211 @comment node-name, next, previous, up
1212 @section The Variable @code{MAKEFILE_LIST}
1213 @cindex makefiles, and @code{MAKEFILE_LIST} variable
1214 @cindex including (@code{MAKEFILE_LIST} variable)
1215 @vindex MAKEFILE_LIST
1217 As @code{make} reads various makefiles, including any obtained from the
1218 @code{MAKEFILES} variable, the command line, the default files, or
1219 from @code{include} directives, their names will be automatically
1220 appended to the @code{MAKEFILE_LIST} variable. They are added right
1221 before @code{make} begins to parse them.
1223 This means that if the first thing a makefile does is examine the last
1224 word in this variable, it will be the name of the current makefile.
1225 Once the current makefile has used @code{include}, however, the last
1226 word will be the just-included makefile.
1228 If a makefile named @code{Makefile} has this content:
1232 name1 := $(lastword $(MAKEFILE_LIST))
1236 name2 := $(lastword $(MAKEFILE_LIST))
1239 @@echo name1 = $(name1)
1240 @@echo name2 = $(name2)
1245 then you would expect to see this output:
1254 @xref{Text Functions}, for more information on the @code{word} and
1255 @code{words} functions used above. @xref{Flavors, The Two Flavors of
1256 Variables}, for more information on simply-expanded (@code{:=})
1257 variable definitions.
1259 @node Special Variables, Remaking Makefiles, MAKEFILE_LIST Variable, Makefiles
1260 @comment node-name, next, previous, up
1261 @section Other Special Variables
1262 @cindex makefiles, and special variables
1263 @cindex special variables
1265 GNU @code{make} also supports other special variables. Unless
1266 otherwise documented here, these values lose their special properties
1267 if they are set by a makefile or on the command line.
1271 @vindex .DEFAULT_GOAL @r{(define default goal)}
1273 Sets the default goal to be used if no targets were specified on the
1274 command line (@pxref{Goals, , Arguments to Specify the Goals}). The
1275 @code{.DEFAULT_GOAL} variable allows you to discover the current
1276 default goal, restart the default goal selection algorithm by clearing
1277 its value, or to explicitly set the default goal. The following
1278 example illustrates these cases:
1282 # Query the default goal.
1283 ifeq ($(.DEFAULT_GOAL),)
1284 $(warning no default goal is set)
1290 $(warning default goal is $(.DEFAULT_GOAL))
1292 # Reset the default goal.
1298 $(warning default goal is $(.DEFAULT_GOAL))
1301 .DEFAULT_GOAL := foo
1305 This makefile prints:
1309 no default goal is set
1316 Note that assigning more than one target name to @code{.DEFAULT_GOAL} is
1317 illegal and will result in an error.
1319 @vindex MAKE_RESTARTS @r{(number of times @code{make} has restarted)}
1321 This variable is set only if this instance of @code{make} has
1322 restarted (@pxref{Remaking Makefiles, , How Makefiles Are Remade}): it
1323 will contain the number of times this instance has restarted. Note
1324 this is not the same as recursion (counted by the @code{MAKELEVEL}
1325 variable). You should not set, modify, or export this variable.
1327 @vindex .VARIABLES @r{(list of variables)}
1329 Expands to a list of the @emph{names} of all global variables defined
1330 so far. This includes variables which have empty values, as well as
1331 built-in variables (@pxref{Implicit Variables, , Variables Used by
1332 Implicit Rules}), but does not include any variables which are only
1333 defined in a target-specific context. Note that any value you assign
1334 to this variable will be ignored; it will always return its special
1337 @c @vindex .TARGETS @r{(list of targets)}
1339 @c The second special variable is @code{.TARGETS}. When expanded, the
1340 @c value consists of a list of all targets defined in all makefiles read
1341 @c up until that point. Note it's not enough for a file to be simply
1342 @c mentioned in the makefile to be listed in this variable, even if it
1343 @c would match an implicit rule and become an ``implicit target''. The
1344 @c file must appear as a target, on the left-hand side of a ``:'', to be
1345 @c considered a target for the purposes of this variable.
1347 @vindex .FEATURES @r{(list of supported features)}
1349 Expands to a list of special features supported by this version of
1350 @code{make}. Possible values include:
1355 Supports @code{ar} (archive) files using special filename syntax.
1356 @xref{Archives, ,Using @code{make} to Update Archive Files}.
1359 Supports the @code{-L} (@code{--check-symlink-times}) flag.
1360 @xref{Options Summary, ,Summary of Options}.
1363 Supports ``else if'' non-nested conditionals. @xref{Conditional
1364 Syntax, ,Syntax of Conditionals}.
1367 Supports ``job server'' enhanced parallel builds. @xref{Parallel,
1368 ,Parallel Execution}.
1370 @item second-expansion
1371 Supports secondary expansion of prerequisite lists.
1374 Supports order-only prerequisites. @xref{Prerequisite Types, ,Types
1377 @item target-specific
1378 Supports target-specific and pattern-specific variable assignments.
1379 @xref{Target-specific, ,Target-specific Variable Values}.
1383 @vindex .INCLUDE_DIRS @r{(list of include directories)}
1385 Expands to a list of directories that @code{make} searches for
1386 included makefiles (@pxref{Include, , Including Other Makefiles}).
1390 @node Remaking Makefiles, Overriding Makefiles, Special Variables, Makefiles
1391 @section How Makefiles Are Remade
1393 @cindex updating makefiles
1394 @cindex remaking makefiles
1395 @cindex makefile, remaking of
1396 Sometimes makefiles can be remade from other files, such as RCS or SCCS
1397 files. If a makefile can be remade from other files, you probably want
1398 @code{make} to get an up-to-date version of the makefile to read in.
1400 To this end, after reading in all makefiles, @code{make} will consider
1401 each as a goal target and attempt to update it. If a makefile has a
1402 rule which says how to update it (found either in that very makefile or
1403 in another one) or if an implicit rule applies to it (@pxref{Implicit
1404 Rules, ,Using Implicit Rules}), it will be updated if necessary. After
1405 all makefiles have been checked, if any have actually been changed,
1406 @code{make} starts with a clean slate and reads all the makefiles over
1407 again. (It will also attempt to update each of them over again, but
1408 normally this will not change them again, since they are already up to
1411 If you know that one or more of your makefiles cannot be remade and you
1412 want to keep @code{make} from performing an implicit rule search on
1413 them, perhaps for efficiency reasons, you can use any normal method of
1414 preventing implicit rule lookup to do so. For example, you can write an
1415 explicit rule with the makefile as the target, and an empty command
1416 string (@pxref{Empty Commands, ,Using Empty Commands}).
1418 If the makefiles specify a double-colon rule to remake a file with
1419 commands but no prerequisites, that file will always be remade
1420 (@pxref{Double-Colon}). In the case of makefiles, a makefile that has a
1421 double-colon rule with commands but no prerequisites will be remade every
1422 time @code{make} is run, and then again after @code{make} starts over
1423 and reads the makefiles in again. This would cause an infinite loop:
1424 @code{make} would constantly remake the makefile, and never do anything
1425 else. So, to avoid this, @code{make} will @strong{not} attempt to
1426 remake makefiles which are specified as targets of a double-colon rule
1427 with commands but no prerequisites.@refill
1429 If you do not specify any makefiles to be read with @samp{-f} or
1430 @samp{--file} options, @code{make} will try the default makefile names;
1431 @pxref{Makefile Names, ,What Name to Give Your Makefile}. Unlike
1432 makefiles explicitly requested with @samp{-f} or @samp{--file} options,
1433 @code{make} is not certain that these makefiles should exist. However,
1434 if a default makefile does not exist but can be created by running
1435 @code{make} rules, you probably want the rules to be run so that the
1436 makefile can be used.
1438 Therefore, if none of the default makefiles exists, @code{make} will try
1439 to make each of them in the same order in which they are searched for
1440 (@pxref{Makefile Names, ,What Name to Give Your Makefile})
1441 until it succeeds in making one, or it runs out of names to try. Note
1442 that it is not an error if @code{make} cannot find or make any makefile;
1443 a makefile is not always necessary.@refill
1445 When you use the @samp{-t} or @samp{--touch} option
1446 (@pxref{Instead of Execution, ,Instead of Executing the Commands}),
1447 you would not want to use an out-of-date makefile to decide which
1448 targets to touch. So the @samp{-t} option has no effect on updating
1449 makefiles; they are really updated even if @samp{-t} is specified.
1450 Likewise, @samp{-q} (or @samp{--question}) and @samp{-n} (or
1451 @samp{--just-print}) do not prevent updating of makefiles, because an
1452 out-of-date makefile would result in the wrong output for other targets.
1453 Thus, @samp{make -f mfile -n foo} will update @file{mfile}, read it in,
1454 and then print the commands to update @file{foo} and its prerequisites
1455 without running them. The commands printed for @file{foo} will be those
1456 specified in the updated contents of @file{mfile}.
1458 However, on occasion you might actually wish to prevent updating of even
1459 the makefiles. You can do this by specifying the makefiles as goals in
1460 the command line as well as specifying them as makefiles. When the
1461 makefile name is specified explicitly as a goal, the options @samp{-t}
1462 and so on do apply to them.
1464 Thus, @samp{make -f mfile -n mfile foo} would read the makefile
1465 @file{mfile}, print the commands needed to update it without actually
1466 running them, and then print the commands needed to update @file{foo}
1467 without running them. The commands for @file{foo} will be those
1468 specified by the existing contents of @file{mfile}.
1470 @node Overriding Makefiles, Reading Makefiles, Remaking Makefiles, Makefiles
1471 @section Overriding Part of Another Makefile
1473 @cindex overriding makefiles
1474 @cindex makefile, overriding
1475 Sometimes it is useful to have a makefile that is mostly just like
1476 another makefile. You can often use the @samp{include} directive to
1477 include one in the other, and add more targets or variable definitions.
1478 However, if the two makefiles give different commands for the same
1479 target, @code{make} will not let you just do this. But there is another way.
1481 @cindex match-anything rule, used to override
1482 In the containing makefile (the one that wants to include the other),
1483 you can use a match-anything pattern rule to say that to remake any
1484 target that cannot be made from the information in the containing
1485 makefile, @code{make} should look in another makefile.
1486 @xref{Pattern Rules}, for more information on pattern rules.
1488 For example, if you have a makefile called @file{Makefile} that says how
1489 to make the target @samp{foo} (and other targets), you can write a
1490 makefile called @file{GNUmakefile} that contains:
1497 @@$(MAKE) -f Makefile $@@
1501 If you say @samp{make foo}, @code{make} will find @file{GNUmakefile},
1502 read it, and see that to make @file{foo}, it needs to run the command
1503 @samp{frobnicate > foo}. If you say @samp{make bar}, @code{make} will
1504 find no way to make @file{bar} in @file{GNUmakefile}, so it will use the
1505 commands from the pattern rule: @samp{make -f Makefile bar}. If
1506 @file{Makefile} provides a rule for updating @file{bar}, @code{make}
1507 will apply the rule. And likewise for any other target that
1508 @file{GNUmakefile} does not say how to make.
1510 The way this works is that the pattern rule has a pattern of just
1511 @samp{%}, so it matches any target whatever. The rule specifies a
1512 prerequisite @file{force}, to guarantee that the commands will be run even
1513 if the target file already exists. We give @file{force} target empty
1514 commands to prevent @code{make} from searching for an implicit rule to
1515 build it---otherwise it would apply the same match-anything rule to
1516 @file{force} itself and create a prerequisite loop!
1518 @node Reading Makefiles, Secondary Expansion, Overriding Makefiles, Makefiles
1519 @section How @code{make} Reads a Makefile
1520 @cindex reading makefiles
1521 @cindex makefile, parsing
1523 GNU @code{make} does its work in two distinct phases. During the first
1524 phase it reads all the makefiles, included makefiles, etc. and
1525 internalizes all the variables and their values, implicit and explicit
1526 rules, and constructs a dependency graph of all the targets and their
1527 prerequisites. During the second phase, @code{make} uses these internal
1528 structures to determine what targets will need to be rebuilt and to
1529 invoke the rules necessary to do so.
1531 It's important to understand this two-phase approach because it has a
1532 direct impact on how variable and function expansion happens; this is
1533 often a source of some confusion when writing makefiles. Here we will
1534 present a summary of the phases in which expansion happens for different
1535 constructs within the makefile. We say that expansion is
1536 @dfn{immediate} if it happens during the first phase: in this case
1537 @code{make} will expand any variables or functions in that section of a
1538 construct as the makefile is parsed. We say that expansion is
1539 @dfn{deferred} if expansion is not performed immediately. Expansion of
1540 deferred construct is not performed until either the construct appears
1541 later in an immediate context, or until the second phase.
1543 You may not be familiar with some of these constructs yet. You can
1544 reference this section as you become familiar with them, in later
1547 @subheading Variable Assignment
1548 @cindex +=, expansion
1549 @cindex =, expansion
1550 @cindex ?=, expansion
1551 @cindex +=, expansion
1552 @cindex define, expansion
1554 Variable definitions are parsed as follows:
1557 @var{immediate} = @var{deferred}
1558 @var{immediate} ?= @var{deferred}
1559 @var{immediate} := @var{immediate}
1560 @var{immediate} += @var{deferred} or @var{immediate}
1562 define @var{immediate}
1567 For the append operator, @samp{+=}, the right-hand side is considered
1568 immediate if the variable was previously set as a simple variable
1569 (@samp{:=}), and deferred otherwise.
1571 @subheading Conditional Statements
1572 @cindex ifdef, expansion
1573 @cindex ifeq, expansion
1574 @cindex ifndef, expansion
1575 @cindex ifneq, expansion
1577 All instances of conditional syntax are parsed immediately, in their
1578 entirety; this includes the @code{ifdef}, @code{ifeq}, @code{ifndef},
1579 and @code{ifneq} forms. Of course this means that automatic variables
1580 cannot be used in conditional statements, as automatic variables are
1581 not set until the command script for that rule is invoked. If you
1582 need to use automatic variables in a conditional you @emph{must} use
1583 shell conditional syntax, in your command script proper, for these
1584 tests, not @code{make} conditionals.
1586 @subheading Rule Definition
1587 @cindex target, expansion
1588 @cindex prerequisite, expansion
1589 @cindex implicit rule, expansion
1590 @cindex pattern rule, expansion
1591 @cindex explicit rule, expansion
1593 A rule is always expanded the same way, regardless of the form:
1596 @var{immediate} : @var{immediate} ; @var{deferred}
1600 That is, the target and prerequisite sections are expanded immediately,
1601 and the commands used to construct the target are always deferred. This
1602 general rule is true for explicit rules, pattern rules, suffix rules,
1603 static pattern rules, and simple prerequisite definitions.
1605 @node Secondary Expansion, , Reading Makefiles, Makefiles
1606 @section Secondary Expansion
1607 @cindex secondary expansion
1608 @cindex expansion, secondary
1610 @findex .SECONDEXPANSION
1611 In the previous section we learned that GNU @code{make} works in two
1612 distinct phases: a read-in phase and a target-update phase
1613 (@pxref{Reading Makefiles, , How @code{make} Reads a Makefile}). GNU
1614 make also has the ability to enable a @emph{second expansion} of the
1615 prerequisites (only) for some or all targets defined in the makefile.
1616 In order for this second expansion to occur, the special target
1617 @code{.SECONDEXPANSION} must be defined before the first prerequisite
1618 list that makes use of this feature.
1620 If that special target is defined then in between the two phases
1621 mentioned above, right at the end of the read-in phase, all the
1622 prerequisites of the targets defined after the special target are
1623 expanded a @emph{second time}. In most circumstances this secondary
1624 expansion will have no effect, since all variable and function
1625 references will have been expanded during the initial parsing of the
1626 makefiles. In order to take advantage of the secondary expansion
1627 phase of the parser, then, it's necessary to @emph{escape} the
1628 variable or function reference in the makefile. In this case the
1629 first expansion merely un-escapes the reference but doesn't expand it,
1630 and expansion is left to the secondary expansion phase. For example,
1631 consider this makefile:
1637 myfile: $(ONEVAR) $$(TWOVAR)
1640 After the first expansion phase the prerequisites list of the
1641 @file{myfile} target will be @code{onefile} and @code{$(TWOVAR)}; the
1642 first (unescaped) variable reference to @var{ONEVAR} is expanded,
1643 while the second (escaped) variable reference is simply unescaped,
1644 without being recognized as a variable reference. Now during the
1645 secondary expansion the first word is expanded again but since it
1646 contains no variable or function references it remains the static
1647 value @file{onefile}, while the second word is now a normal reference
1648 to the variable @var{TWOVAR}, which is expanded to the value
1649 @file{twofile}. The final result is that there are two prerequisites,
1650 @file{onefile} and @file{twofile}.
1652 Obviously, this is not a very interesting case since the same result
1653 could more easily have been achieved simply by having both variables
1654 appear, unescaped, in the prerequisites list. One difference becomes
1655 apparent if the variables are reset; consider this example:
1665 Here the prerequisite of @file{onefile} will be expanded immediately,
1666 and resolve to the value @file{top}, while the prerequisite of
1667 @file{twofile} will not be full expanded until the secondary expansion
1668 and yield a value of @file{bottom}.
1670 This is marginally more exciting, but the true power of this feature
1671 only becomes apparent when you discover that secondary expansions
1672 always take place within the scope of the automatic variables for that
1673 target. This means that you can use variables such as @code{$@@},
1674 @code{$*}, etc. during the second expansion and they will have their
1675 expected values, just as in the command script. All you have to do is
1676 defer the expansion by escaping the @code{$}. Also, secondary
1677 expansion occurs for both explicit and implicit (pattern) rules.
1678 Knowing this, the possible uses for this feature increase
1679 dramatically. For example:
1683 main_OBJS := main.o try.o test.o
1684 lib_OBJS := lib.o api.o
1686 main lib: $$($$@@_OBJS)
1689 Here, after the initial expansion the prerequisites of both the
1690 @file{main} and @file{lib} targets will be @code{$($@@_OBJS)}. During
1691 the secondary expansion, the @code{$@@} variable is set to the name of
1692 the target and so the expansion for the @file{main} target will yield
1693 @code{$(main_OBJS)}, or @code{main.o try.o test.o}, while the
1694 secondary expansion for the @file{lib} target will yield
1695 @code{$(lib_OBJS)}, or @code{lib.o api.o}.
1697 You can also mix functions here, as long as they are properly escaped:
1700 main_SRCS := main.c try.c test.c
1701 lib_SRCS := lib.c api.c
1704 main lib: $$(patsubst %.c,%.o,$$($$@@_SRCS))
1707 This version allows users to specify source files rather than object
1708 files, but gives the same resulting prerequisites list as the previous
1711 Evaluation of automatic variables during the secondary expansion
1712 phase, especially of the target name variable @code{$$@@}, behaves
1713 similarly to evaluation within command scripts. However, there are
1714 some subtle differences and ``corner cases'' which come into play for
1715 the different types of rule definitions that @code{make} understands.
1716 The subtleties of using the different automatic variables are
1719 @subheading Secondary Expansion of Explicit Rules
1720 @cindex secondary expansion and explicit rules
1721 @cindex explicit rules, secondary expansion of
1723 During the secondary expansion of explicit rules, @code{$$@@} and
1724 @code{$$%} evaluate, respectively, to the file name of the target and,
1725 when the target is an archive member, the target member name. The
1726 @code{$$<} variable evaluates to the first prerequisite in the first
1727 rule for this target. @code{$$^} and @code{$$+} evaluate to the list
1728 of all prerequisites of rules @emph{that have already appeared} for
1729 the same target (@code{$$+} with repetitions and @code{$$^}
1730 without). The following example will help illustrate these behaviors:
1735 foo: foo.1 bar.1 $$< $$^ $$+ # line #1
1737 foo: foo.2 bar.2 $$< $$^ $$+ # line #2
1739 foo: foo.3 bar.3 $$< $$^ $$+ # line #3
1742 In the first prerequisite list, all three variables (@code{$$<},
1743 @code{$$^}, and @code{$$+}) expand to the empty string. In the
1744 second, they will have values @code{foo.1}, @code{foo.1 bar.1}, and
1745 @code{foo.1 bar.1} respectively. In the third they will have values
1746 @code{foo.1}, @code{foo.1 bar.1 foo.2 bar.2}, and @code{foo.1 bar.1
1747 foo.2 bar.2} respectively.
1749 Rules undergo secondary expansion in makefile order, except that
1750 the rule with the command script is always evaluated last.
1752 The variables @code{$$?} and @code{$$*} are not available and expand
1753 to the empty string.
1755 @subheading Secondary Expansion of Static Pattern Rules
1756 @cindex secondary expansion and static pattern rules
1757 @cindex static pattern rules, secondary expansion of
1759 Rules for secondary expansion of static pattern rules are identical to
1760 those for explicit rules, above, with one exception: for static
1761 pattern rules the @code{$$*} variable is set to the pattern stem. As
1762 with explicit rules, @code{$$?} is not available and expands to the
1765 @subheading Secondary Expansion of Implicit Rules
1766 @cindex secondary expansion and implicit rules
1767 @cindex implicit rules, secondary expansion of
1769 As @code{make} searches for an implicit rule, it substitutes the stem
1770 and then performs secondary expansion for every rule with a matching
1771 target pattern. The value of the automatic variables is derived in
1772 the same fashion as for static pattern rules. As an example:
1781 %oo: $$< $$^ $$+ $$*
1784 When the implicit rule is tried for target @file{foo}, @code{$$<}
1785 expands to @file{bar}, @code{$$^} expands to @file{bar boo},
1786 @code{$$+} also expands to @file{bar boo}, and @code{$$*} expands to
1789 Note that the directory prefix (D), as described in @ref{Implicit Rule
1790 Search, ,Implicit Rule Search Algorithm}, is appended (after
1791 expansion) to all the patterns in the prerequisites list. As an
1799 %.o: $$(addsuffix /%.c,foo bar) foo.h
1802 The prerequisite list after the secondary expansion and directory
1803 prefix reconstruction will be @file{/tmp/foo/foo.c /tmp/var/bar/foo.c
1804 foo.h}. If you are not interested in this reconstruction, you can use
1805 @code{$$*} instead of @code{%} in the prerequisites list.
1807 @node Rules, Commands, Makefiles, Top
1808 @chapter Writing Rules
1809 @cindex writing rules
1810 @cindex rule, how to write
1812 @cindex prerequisite
1814 A @dfn{rule} appears in the makefile and says when and how to remake
1815 certain files, called the rule's @dfn{targets} (most often only one per rule).
1816 It lists the other files that are the @dfn{prerequisites} of the target, and
1817 @dfn{commands} to use to create or update the target.
1819 @cindex default goal
1820 @cindex goal, default
1821 The order of rules is not significant, except for determining the
1822 @dfn{default goal}: the target for @code{make} to consider, if you do
1823 not otherwise specify one. The default goal is the target of the first
1824 rule in the first makefile. If the first rule has multiple targets,
1825 only the first target is taken as the default. There are two
1826 exceptions: a target starting with a period is not a default unless it
1827 contains one or more slashes, @samp{/}, as well; and, a target that
1828 defines a pattern rule has no effect on the default goal.
1829 (@xref{Pattern Rules, ,Defining and Redefining Pattern Rules}.)
1831 Therefore, we usually write the makefile so that the first rule is the
1832 one for compiling the entire program or all the programs described by
1833 the makefile (often with a target called @samp{all}).
1834 @xref{Goals, ,Arguments to Specify the Goals}.
1837 * Rule Example:: An example explained.
1838 * Rule Syntax:: General syntax explained.
1839 * Prerequisite Types:: There are two types of prerequisites.
1840 * Wildcards:: Using wildcard characters such as `*'.
1841 * Directory Search:: Searching other directories for source files.
1842 * Phony Targets:: Using a target that is not a real file's name.
1843 * Force Targets:: You can use a target without commands
1844 or prerequisites to mark other targets
1846 * Empty Targets:: When only the date matters and the
1848 * Special Targets:: Targets with special built-in meanings.
1849 * Multiple Targets:: When to make use of several targets in a rule.
1850 * Multiple Rules:: How to use several rules with the same target.
1851 * Static Pattern:: Static pattern rules apply to multiple targets
1852 and can vary the prerequisites according to
1854 * Double-Colon:: How to use a special kind of rule to allow
1855 several independent rules for one target.
1856 * Automatic Prerequisites:: How to automatically generate rules giving
1857 prerequisites from source files themselves.
1861 @node Rule Example, Rule Syntax, Rules, Rules
1862 @section Rule Example
1864 Here is an example of a rule:
1867 foo.o : foo.c defs.h # module for twiddling the frobs
1871 Its target is @file{foo.o} and its prerequisites are @file{foo.c} and
1872 @file{defs.h}. It has one command, which is @samp{cc -c -g foo.c}.
1873 The command line starts with a tab to identify it as a command.
1875 This rule says two things:
1879 How to decide whether @file{foo.o} is out of date: it is out of date
1880 if it does not exist, or if either @file{foo.c} or @file{defs.h} is
1881 more recent than it.
1884 How to update the file @file{foo.o}: by running @code{cc} as stated.
1885 The command does not explicitly mention @file{defs.h}, but we presume
1886 that @file{foo.c} includes it, and that that is why @file{defs.h} was
1887 added to the prerequisites.
1891 @node Rule Syntax, Prerequisite Types, Rule Example, Rules
1892 @section Rule Syntax
1895 @cindex syntax of rules
1896 In general, a rule looks like this:
1899 @var{targets} : @var{prerequisites}
1908 @var{targets} : @var{prerequisites} ; @var{command}
1914 @cindex rule targets
1915 The @var{targets} are file names, separated by spaces. Wildcard
1916 characters may be used (@pxref{Wildcards, ,Using Wildcard Characters
1917 in File Names}) and a name of the form @file{@var{a}(@var{m})}
1918 represents member @var{m} in archive file @var{a}
1919 (@pxref{Archive Members, ,Archive Members as Targets}).
1920 Usually there is only one
1921 target per rule, but occasionally there is a reason to have more
1922 (@pxref{Multiple Targets, , Multiple Targets in a Rule}).@refill
1925 @cindex tab character (in commands)
1926 The @var{command} lines start with a tab character. The first command may
1927 appear on the line after the prerequisites, with a tab character, or may
1928 appear on the same line, with a semicolon. Either way, the effect is the
1929 same. There are other differences in the syntax of command lines.
1930 @xref{Commands, ,Writing the Commands in Rules}.
1932 @cindex dollar sign (@code{$}), in rules
1933 @cindex @code{$}, in rules
1934 @cindex rules, and @code{$}
1935 Because dollar signs are used to start @code{make} variable
1936 references, if you really want a dollar sign in a target or
1937 prerequisite you must write two of them, @samp{$$} (@pxref{Using
1938 Variables, ,How to Use Variables}). If you have enabled secondary
1939 expansion (@pxref{Secondary Expansion}) and you want a literal dollar
1940 sign in the prerequisites lise, you must actually write @emph{four}
1941 dollar signs (@samp{$$$$}).
1943 You may split a long line by inserting a backslash followed by a
1944 newline, but this is not required, as @code{make} places no limit on
1945 the length of a line in a makefile.
1947 A rule tells @code{make} two things: when the targets are out of date,
1948 and how to update them when necessary.
1950 @cindex prerequisites
1951 @cindex rule prerequisites
1952 The criterion for being out of date is specified in terms of the
1953 @var{prerequisites}, which consist of file names separated by spaces.
1954 (Wildcards and archive members (@pxref{Archives}) are allowed here too.)
1955 A target is out of date if it does not exist or if it is older than any
1956 of the prerequisites (by comparison of last-modification times). The
1957 idea is that the contents of the target file are computed based on
1958 information in the prerequisites, so if any of the prerequisites changes,
1959 the contents of the existing target file are no longer necessarily
1962 How to update is specified by @var{commands}. These are lines to be
1963 executed by the shell (normally @samp{sh}), but with some extra features
1964 (@pxref{Commands, ,Writing the Commands in Rules}).
1966 @node Prerequisite Types, Wildcards, Rule Syntax, Rules
1967 @comment node-name, next, previous, up
1968 @section Types of Prerequisites
1969 @cindex prerequisite types
1970 @cindex types of prerequisites
1972 @cindex prerequisites, normal
1973 @cindex normal prerequisites
1974 @cindex prerequisites, order-only
1975 @cindex order-only prerequisites
1976 There are actually two different types of prerequisites understood by
1977 GNU @code{make}: normal prerequisites such as described in the
1978 previous section, and @dfn{order-only} prerequisites. A normal
1979 prerequisite makes two statements: first, it imposes an order of
1980 execution of build commands: any commands necessary to build any of a
1981 target's prerequisites will be fully executed before any commands
1982 necessary to build the target. Second, it imposes a dependency
1983 relationship: if any prerequisite is newer than the target, then the
1984 target is considered out-of-date and must be rebuilt.
1986 Normally, this is exactly what you want: if a target's prerequisite is
1987 updated, then the target should also be updated.
1989 Occasionally, however, you have a situation where you want to impose a
1990 specific ordering on the rules to be invoked @emph{without} forcing
1991 the target to be updated if one of those rules is executed. In that
1992 case, you want to define @dfn{order-only} prerequisites. Order-only
1993 prerequisites can be specified by placing a pipe symbol (@code{|})
1994 in the prerequisites list: any prerequisites to the left of the pipe
1995 symbol are normal; any prerequisites to the right are order-only:
1998 @var{targets} : @var{normal-prerequisites} | @var{order-only-prerequisites}
2001 The normal prerequisites section may of course be empty. Also, you
2002 may still declare multiple lines of prerequisites for the same target:
2003 they are appended appropriately. Note that if you declare the same
2004 file to be both a normal and an order-only prerequisite, the normal
2005 prerequisite takes precedence (since they are a strict superset of the
2006 behavior of an order-only prerequisite).
2008 @node Wildcards, Directory Search, Prerequisite Types, Rules
2009 @section Using Wildcard Characters in File Names
2011 @cindex file name with wildcards
2012 @cindex globbing (wildcards)
2014 @cindex @code{*} (wildcard character)
2015 @cindex @code{?} (wildcard character)
2016 @cindex @code{[@dots{}]} (wildcard characters)
2017 A single file name can specify many files using @dfn{wildcard characters}.
2018 The wildcard characters in @code{make} are @samp{*}, @samp{?} and
2019 @samp{[@dots{}]}, the same as in the Bourne shell. For example, @file{*.c}
2020 specifies a list of all the files (in the working directory) whose names
2021 end in @samp{.c}.@refill
2023 @cindex @code{~} (tilde)
2024 @cindex tilde (@code{~})
2025 @cindex home directory
2026 The character @samp{~} at the beginning of a file name also has special
2027 significance. If alone, or followed by a slash, it represents your home
2028 directory. For example @file{~/bin} expands to @file{/home/you/bin}.
2029 If the @samp{~} is followed by a word, the string represents the home
2030 directory of the user named by that word. For example @file{~john/bin}
2031 expands to @file{/home/john/bin}. On systems which don't have a home
2032 directory for each user (such as MS-DOS or MS-Windows), this
2033 functionality can be simulated by setting the environment variable
2036 Wildcard expansion is performed by @code{make} automatically in
2037 targets and in prerequisites. In commands the shell is responsible
2038 for wildcard expansion. In other contexts, wildcard expansion happens
2039 only if you request it explicitly with the @code{wildcard} function.
2041 The special significance of a wildcard character can be turned off by
2042 preceding it with a backslash. Thus, @file{foo\*bar} would refer to a
2043 specific file whose name consists of @samp{foo}, an asterisk, and
2047 * Wildcard Examples:: Several examples
2048 * Wildcard Pitfall:: Problems to avoid.
2049 * Wildcard Function:: How to cause wildcard expansion where
2050 it does not normally take place.
2053 @node Wildcard Examples, Wildcard Pitfall, Wildcards, Wildcards
2054 @subsection Wildcard Examples
2056 Wildcards can be used in the commands of a rule, where they are expanded
2057 by the shell. For example, here is a rule to delete all the object files:
2065 @cindex @code{rm} (shell command)
2067 Wildcards are also useful in the prerequisites of a rule. With the
2068 following rule in the makefile, @samp{make print} will print all the
2069 @samp{.c} files that have changed since the last time you printed them:
2077 @cindex @code{print} target
2078 @cindex @code{lpr} (shell command)
2079 @cindex @code{touch} (shell command)
2081 This rule uses @file{print} as an empty target file; see @ref{Empty
2082 Targets, ,Empty Target Files to Record Events}. (The automatic variable
2083 @samp{$?} is used to print only those files that have changed; see
2084 @ref{Automatic Variables}.)@refill
2086 Wildcard expansion does not happen when you define a variable. Thus, if
2094 then the value of the variable @code{objects} is the actual string
2095 @samp{*.o}. However, if you use the value of @code{objects} in a target,
2096 prerequisite or command, wildcard expansion will take place at that time.
2097 To set @code{objects} to the expansion, instead use:
2100 objects := $(wildcard *.o)
2104 @xref{Wildcard Function}.
2106 @node Wildcard Pitfall, Wildcard Function, Wildcard Examples, Wildcards
2107 @subsection Pitfalls of Using Wildcards
2108 @cindex wildcard pitfalls
2109 @cindex pitfalls of wildcards
2110 @cindex mistakes with wildcards
2111 @cindex errors with wildcards
2112 @cindex problems with wildcards
2114 Now here is an example of a naive way of using wildcard expansion, that
2115 does not do what you would intend. Suppose you would like to say that the
2116 executable file @file{foo} is made from all the object files in the
2117 directory, and you write this:
2123 cc -o foo $(CFLAGS) $(objects)
2127 The value of @code{objects} is the actual string @samp{*.o}. Wildcard
2128 expansion happens in the rule for @file{foo}, so that each @emph{existing}
2129 @samp{.o} file becomes a prerequisite of @file{foo} and will be recompiled if
2132 But what if you delete all the @samp{.o} files? When a wildcard matches
2133 no files, it is left as it is, so then @file{foo} will depend on the
2134 oddly-named file @file{*.o}. Since no such file is likely to exist,
2135 @code{make} will give you an error saying it cannot figure out how to
2136 make @file{*.o}. This is not what you want!
2138 Actually it is possible to obtain the desired result with wildcard
2139 expansion, but you need more sophisticated techniques, including the
2140 @code{wildcard} function and string substitution.
2142 @xref{Wildcard Function, ,The Function @code{wildcard}}.
2145 These are described in the following section.
2148 @cindex wildcards and MS-DOS/MS-Windows backslashes
2149 @cindex backslashes in pathnames and wildcard expansion
2151 Microsoft operating systems (MS-DOS and MS-Windows) use backslashes to
2152 separate directories in pathnames, like so:
2158 This is equivalent to the Unix-style @file{c:/foo/bar/baz.c} (the
2159 @file{c:} part is the so-called drive letter). When @code{make} runs on
2160 these systems, it supports backslashes as well as the Unix-style forward
2161 slashes in pathnames. However, this support does @emph{not} include the
2162 wildcard expansion, where backslash is a quote character. Therefore,
2163 you @emph{must} use Unix-style slashes in these cases.
2166 @node Wildcard Function, , Wildcard Pitfall, Wildcards
2167 @subsection The Function @code{wildcard}
2170 Wildcard expansion happens automatically in rules. But wildcard expansion
2171 does not normally take place when a variable is set, or inside the
2172 arguments of a function. If you want to do wildcard expansion in such
2173 places, you need to use the @code{wildcard} function, like this:
2176 $(wildcard @var{pattern}@dots{})
2180 This string, used anywhere in a makefile, is replaced by a
2181 space-separated list of names of existing files that match one of the
2182 given file name patterns. If no existing file name matches a pattern,
2183 then that pattern is omitted from the output of the @code{wildcard}
2184 function. Note that this is different from how unmatched wildcards
2185 behave in rules, where they are used verbatim rather than ignored
2186 (@pxref{Wildcard Pitfall}).
2188 One use of the @code{wildcard} function is to get a list of all the C source
2189 files in a directory, like this:
2195 We can change the list of C source files into a list of object files by
2196 replacing the @samp{.c} suffix with @samp{.o} in the result, like this:
2199 $(patsubst %.c,%.o,$(wildcard *.c))
2203 (Here we have used another function, @code{patsubst}.
2204 @xref{Text Functions, ,Functions for String Substitution and Analysis}.)@refill
2206 Thus, a makefile to compile all C source files in the directory and then
2207 link them together could be written as follows:
2210 objects := $(patsubst %.c,%.o,$(wildcard *.c))
2213 cc -o foo $(objects)
2217 (This takes advantage of the implicit rule for compiling C programs, so
2218 there is no need to write explicit rules for compiling the files.
2219 @xref{Flavors, ,The Two Flavors of Variables}, for an explanation of
2220 @samp{:=}, which is a variant of @samp{=}.)
2222 @node Directory Search, Phony Targets, Wildcards, Rules
2223 @section Searching Directories for Prerequisites
2227 @cindex search path for prerequisites (@code{VPATH})
2228 @cindex directory search (@code{VPATH})
2230 For large systems, it is often desirable to put sources in a separate
2231 directory from the binaries. The @dfn{directory search} features of
2232 @code{make} facilitate this by searching several directories
2233 automatically to find a prerequisite. When you redistribute the files
2234 among directories, you do not need to change the individual rules,
2235 just the search paths.
2238 * General Search:: Specifying a search path that applies
2239 to every prerequisite.
2240 * Selective Search:: Specifying a search path
2241 for a specified class of names.
2242 * Search Algorithm:: When and how search paths are applied.
2243 * Commands/Search:: How to write shell commands that work together
2245 * Implicit/Search:: How search paths affect implicit rules.
2246 * Libraries/Search:: Directory search for link libraries.
2249 @node General Search, Selective Search, Directory Search, Directory Search
2250 @subsection @code{VPATH}: Search Path for All Prerequisites
2253 The value of the @code{make} variable @code{VPATH} specifies a list of
2254 directories that @code{make} should search. Most often, the
2255 directories are expected to contain prerequisite files that are not in the
2256 current directory; however, @code{make} uses @code{VPATH} as a search
2257 list for both prerequisites and targets of rules.
2259 Thus, if a file that is listed as a target or prerequisite does not exist
2260 in the current directory, @code{make} searches the directories listed in
2261 @code{VPATH} for a file with that name. If a file is found in one of
2262 them, that file may become the prerequisite (see below). Rules may then
2263 specify the names of files in the prerequisite list as if they all
2264 existed in the current directory. @xref{Commands/Search, ,Writing Shell
2265 Commands with Directory Search}.
2267 In the @code{VPATH} variable, directory names are separated by colons or
2268 blanks. The order in which directories are listed is the order followed
2269 by @code{make} in its search. (On MS-DOS and MS-Windows, semi-colons
2270 are used as separators of directory names in @code{VPATH}, since the
2271 colon can be used in the pathname itself, after the drive letter.)
2276 VPATH = src:../headers
2280 specifies a path containing two directories, @file{src} and
2281 @file{../headers}, which @code{make} searches in that order.
2283 With this value of @code{VPATH}, the following rule,
2290 is interpreted as if it were written like this:
2297 assuming the file @file{foo.c} does not exist in the current directory but
2298 is found in the directory @file{src}.
2300 @node Selective Search, Search Algorithm, General Search, Directory Search
2301 @subsection The @code{vpath} Directive
2304 Similar to the @code{VPATH} variable, but more selective, is the
2305 @code{vpath} directive (note lower case), which allows you to specify a
2306 search path for a particular class of file names: those that match a
2307 particular pattern. Thus you can supply certain search directories for
2308 one class of file names and other directories (or none) for other file
2311 There are three forms of the @code{vpath} directive:
2314 @item vpath @var{pattern} @var{directories}
2315 Specify the search path @var{directories} for file names that match
2318 The search path, @var{directories}, is a list of directories to be
2319 searched, separated by colons (semi-colons on MS-DOS and MS-Windows) or
2320 blanks, just like the search path used in the @code{VPATH} variable.
2322 @item vpath @var{pattern}
2323 Clear out the search path associated with @var{pattern}.
2325 @c Extra blank line makes sure this gets two lines.
2328 Clear all search paths previously specified with @code{vpath} directives.
2331 A @code{vpath} pattern is a string containing a @samp{%} character. The
2332 string must match the file name of a prerequisite that is being searched
2333 for, the @samp{%} character matching any sequence of zero or more
2334 characters (as in pattern rules; @pxref{Pattern Rules, ,Defining and
2335 Redefining Pattern Rules}). For example, @code{%.h} matches files that
2336 end in @code{.h}. (If there is no @samp{%}, the pattern must match the
2337 prerequisite exactly, which is not useful very often.)
2339 @cindex @code{%}, quoting in @code{vpath}
2340 @cindex @code{%}, quoting with @code{\} (backslash)
2341 @cindex @code{\} (backslash), to quote @code{%}
2342 @cindex backslash (@code{\}), to quote @code{%}
2343 @cindex quoting @code{%}, in @code{vpath}
2344 @samp{%} characters in a @code{vpath} directive's pattern can be quoted
2345 with preceding backslashes (@samp{\}). Backslashes that would otherwise
2346 quote @samp{%} characters can be quoted with more backslashes.
2347 Backslashes that quote @samp{%} characters or other backslashes are
2348 removed from the pattern before it is compared to file names. Backslashes
2349 that are not in danger of quoting @samp{%} characters go unmolested.@refill
2351 When a prerequisite fails to exist in the current directory, if the
2352 @var{pattern} in a @code{vpath} directive matches the name of the
2353 prerequisite file, then the @var{directories} in that directive are searched
2354 just like (and before) the directories in the @code{VPATH} variable.
2359 vpath %.h ../headers
2363 tells @code{make} to look for any prerequisite whose name ends in @file{.h}
2364 in the directory @file{../headers} if the file is not found in the current
2367 If several @code{vpath} patterns match the prerequisite file's name, then
2368 @code{make} processes each matching @code{vpath} directive one by one,
2369 searching all the directories mentioned in each directive. @code{make}
2370 handles multiple @code{vpath} directives in the order in which they
2371 appear in the makefile; multiple directives with the same pattern are
2372 independent of each other.
2386 will look for a file ending in @samp{.c} in @file{foo}, then
2387 @file{blish}, then @file{bar}, while
2397 will look for a file ending in @samp{.c} in @file{foo}, then
2398 @file{bar}, then @file{blish}.
2400 @node Search Algorithm, Commands/Search, Selective Search, Directory Search
2401 @subsection How Directory Searches are Performed
2402 @cindex algorithm for directory search
2403 @cindex directory search algorithm
2405 When a prerequisite is found through directory search, regardless of type
2406 (general or selective), the pathname located may not be the one that
2407 @code{make} actually provides you in the prerequisite list. Sometimes
2408 the path discovered through directory search is thrown away.
2410 The algorithm @code{make} uses to decide whether to keep or abandon a
2411 path found via directory search is as follows:
2415 If a target file does not exist at the path specified in the makefile,
2416 directory search is performed.
2419 If the directory search is successful, that path is kept and this file
2420 is tentatively stored as the target.
2423 All prerequisites of this target are examined using this same method.
2426 After processing the prerequisites, the target may or may not need to be
2431 If the target does @emph{not} need to be rebuilt, the path to the file
2432 found during directory search is used for any prerequisite lists which
2433 contain this target. In short, if @code{make} doesn't need to rebuild
2434 the target then you use the path found via directory search.
2437 If the target @emph{does} need to be rebuilt (is out-of-date), the
2438 pathname found during directory search is @emph{thrown away}, and the
2439 target is rebuilt using the file name specified in the makefile. In
2440 short, if @code{make} must rebuild, then the target is rebuilt locally,
2441 not in the directory found via directory search.
2445 This algorithm may seem complex, but in practice it is quite often
2446 exactly what you want.
2448 @cindex traditional directory search (GPATH)
2449 @cindex directory search, traditional (GPATH)
2450 Other versions of @code{make} use a simpler algorithm: if the file does
2451 not exist, and it is found via directory search, then that pathname is
2452 always used whether or not the target needs to be built. Thus, if the
2453 target is rebuilt it is created at the pathname discovered during
2457 If, in fact, this is the behavior you want for some or all of your
2458 directories, you can use the @code{GPATH} variable to indicate this to
2461 @code{GPATH} has the same syntax and format as @code{VPATH} (that is, a
2462 space- or colon-delimited list of pathnames). If an out-of-date target
2463 is found by directory search in a directory that also appears in
2464 @code{GPATH}, then that pathname is not thrown away. The target is
2465 rebuilt using the expanded path.
2467 @node Commands/Search, Implicit/Search, Search Algorithm, Directory Search
2468 @subsection Writing Shell Commands with Directory Search
2469 @cindex shell command, and directory search
2470 @cindex directory search (@code{VPATH}), and shell commands
2472 When a prerequisite is found in another directory through directory search,
2473 this cannot change the commands of the rule; they will execute as written.
2474 Therefore, you must write the commands with care so that they will look for
2475 the prerequisite in the directory where @code{make} finds it.
2477 This is done with the @dfn{automatic variables} such as @samp{$^}
2478 (@pxref{Automatic Variables}).
2479 For instance, the value of @samp{$^} is a
2480 list of all the prerequisites of the rule, including the names of
2481 the directories in which they were found, and the value of
2482 @samp{$@@} is the target. Thus:@refill
2486 cc -c $(CFLAGS) $^ -o $@@
2490 (The variable @code{CFLAGS} exists so you can specify flags for C
2491 compilation by implicit rules; we use it here for consistency so it will
2492 affect all C compilations uniformly;
2493 @pxref{Implicit Variables, ,Variables Used by Implicit Rules}.)
2495 Often the prerequisites include header files as well, which you do not
2496 want to mention in the commands. The automatic variable @samp{$<} is
2497 just the first prerequisite:
2500 VPATH = src:../headers
2501 foo.o : foo.c defs.h hack.h
2502 cc -c $(CFLAGS) $< -o $@@
2505 @node Implicit/Search, Libraries/Search, Commands/Search, Directory Search
2506 @subsection Directory Search and Implicit Rules
2507 @cindex @code{VPATH}, and implicit rules
2508 @cindex directory search (@code{VPATH}), and implicit rules
2509 @cindex search path for prerequisites (@code{VPATH}), and implicit rules
2510 @cindex implicit rule, and directory search
2511 @cindex implicit rule, and @code{VPATH}
2512 @cindex rule, implicit, and directory search
2513 @cindex rule, implicit, and @code{VPATH}
2515 The search through the directories specified in @code{VPATH} or with
2516 @code{vpath} also happens during consideration of implicit rules
2517 (@pxref{Implicit Rules, ,Using Implicit Rules}).
2519 For example, when a file @file{foo.o} has no explicit rule, @code{make}
2520 considers implicit rules, such as the built-in rule to compile
2521 @file{foo.c} if that file exists. If such a file is lacking in the
2522 current directory, the appropriate directories are searched for it. If
2523 @file{foo.c} exists (or is mentioned in the makefile) in any of the
2524 directories, the implicit rule for C compilation is applied.
2526 The commands of implicit rules normally use automatic variables as a
2527 matter of necessity; consequently they will use the file names found by
2528 directory search with no extra effort.
2530 @node Libraries/Search, , Implicit/Search, Directory Search
2531 @subsection Directory Search for Link Libraries
2532 @cindex link libraries, and directory search
2533 @cindex libraries for linking, directory search
2534 @cindex directory search (@code{VPATH}), and link libraries
2535 @cindex @code{VPATH}, and link libraries
2536 @cindex search path for prerequisites (@code{VPATH}), and link libraries
2537 @cindex @code{-l} (library search)
2538 @cindex link libraries, patterns matching
2539 @cindex @code{.LIBPATTERNS}, and link libraries
2540 @vindex .LIBPATTERNS
2542 Directory search applies in a special way to libraries used with the
2543 linker. This special feature comes into play when you write a prerequisite
2544 whose name is of the form @samp{-l@var{name}}. (You can tell something
2545 strange is going on here because the prerequisite is normally the name of a
2546 file, and the @emph{file name} of a library generally looks like
2547 @file{lib@var{name}.a}, not like @samp{-l@var{name}}.)@refill
2549 When a prerequisite's name has the form @samp{-l@var{name}}, @code{make}
2550 handles it specially by searching for the file @file{lib@var{name}.so} in
2551 the current directory, in directories specified by matching @code{vpath}
2552 search paths and the @code{VPATH} search path, and then in the
2553 directories @file{/lib}, @file{/usr/lib}, and @file{@var{prefix}/lib}
2554 (normally @file{/usr/local/lib}, but MS-DOS/MS-Windows versions of
2555 @code{make} behave as if @var{prefix} is defined to be the root of the
2556 DJGPP installation tree).
2558 If that file is not found, then the file @file{lib@var{name}.a} is
2559 searched for, in the same directories as above.
2561 For example, if there is a @file{/usr/lib/libcurses.a} library on your
2562 system (and no @file{/usr/lib/libcurses.so} file), then
2566 foo : foo.c -lcurses
2572 would cause the command @samp{cc foo.c /usr/lib/libcurses.a -o foo} to
2573 be executed when @file{foo} is older than @file{foo.c} or than
2574 @file{/usr/lib/libcurses.a}.@refill
2576 Although the default set of files to be searched for is
2577 @file{lib@var{name}.so} and @file{lib@var{name}.a}, this is customizable
2578 via the @code{.LIBPATTERNS} variable. Each word in the value of this
2579 variable is a pattern string. When a prerequisite like
2580 @samp{-l@var{name}} is seen, @code{make} will replace the percent in
2581 each pattern in the list with @var{name} and perform the above directory
2582 searches using that library filename. If no library is found, the next
2583 word in the list will be used.
2585 The default value for @code{.LIBPATTERNS} is @samp{lib%.so lib%.a},
2586 which provides the default behavior described above.
2588 You can turn off link library expansion completely by setting this
2589 variable to an empty value.
2591 @node Phony Targets, Force Targets, Directory Search, Rules
2592 @section Phony Targets
2593 @cindex phony targets
2594 @cindex targets, phony
2595 @cindex targets without a file
2597 A phony target is one that is not really the name of a file. It is just a
2598 name for some commands to be executed when you make an explicit request.
2599 There are two reasons to use a phony target: to avoid a conflict with
2600 a file of the same name, and to improve performance.
2602 If you write a rule whose commands will not create the target file, the
2603 commands will be executed every time the target comes up for remaking.
2614 Because the @code{rm} command does not create a file named @file{clean},
2615 probably no such file will ever exist. Therefore, the @code{rm} command
2616 will be executed every time you say @samp{make clean}.
2617 @cindex @code{rm} (shell command)
2620 The phony target will cease to work if anything ever does create a file
2621 named @file{clean} in this directory. Since it has no prerequisites, the
2622 file @file{clean} would inevitably be considered up to date, and its
2623 commands would not be executed. To avoid this problem, you can explicitly
2624 declare the target to be phony, using the special target @code{.PHONY}
2625 (@pxref{Special Targets, ,Special Built-in Target Names}) as follows:
2632 Once this is done, @samp{make clean} will run the commands regardless of
2633 whether there is a file named @file{clean}.
2635 Since it knows that phony targets do not name actual files that could be
2636 remade from other files, @code{make} skips the implicit rule search for
2637 phony targets (@pxref{Implicit Rules}). This is why declaring a target
2638 phony is good for performance, even if you are not worried about the
2639 actual file existing.
2641 Thus, you first write the line that states that @code{clean} is a
2642 phony target, then you write the rule, like this:
2652 Another example of the usefulness of phony targets is in conjunction
2653 with recursive invocations of @code{make} (for more information, see
2654 @ref{Recursion, ,Recursive Use of @code{make}}). In this case the
2655 makefile will often contain a variable which lists a number of
2656 subdirectories to be built. One way to handle this is with one rule
2657 whose command is a shell loop over the subdirectories, like this:
2661 SUBDIRS = foo bar baz
2664 for dir in $(SUBDIRS); do \
2670 There are a few problems with this method, however. First, any error
2671 detected in a submake is not noted by this rule, so it will continue to
2672 build the rest of the directories even when one fails. This can be
2673 overcome by adding shell commands to note the error and exit, but then
2674 it will do so even if @code{make} is invoked with the @code{-k} option,
2675 which is unfortunate. Second, and perhaps more importantly, you cannot
2676 take advantage of @code{make}'s ability to build targets in parallel
2677 (@pxref{Parallel, ,Parallel Execution}), since there is only one rule.
2679 By declaring the subdirectories as phony targets (you must do this as
2680 the subdirectory obviously always exists; otherwise it won't be built)
2681 you can remove these problems:
2685 SUBDIRS = foo bar baz
2687 .PHONY: subdirs $(SUBDIRS)
2698 Here we've also declared that the @file{foo} subdirectory cannot be
2699 built until after the @file{baz} subdirectory is complete; this kind of
2700 relationship declaration is particularly important when attempting
2703 A phony target should not be a prerequisite of a real target file; if it
2704 is, its commands are run every time @code{make} goes to update that
2705 file. As long as a phony target is never a prerequisite of a real
2706 target, the phony target commands will be executed only when the phony
2707 target is a specified goal (@pxref{Goals, ,Arguments to Specify the
2710 Phony targets can have prerequisites. When one directory contains multiple
2711 programs, it is most convenient to describe all of the programs in one
2712 makefile @file{./Makefile}. Since the target remade by default will be the
2713 first one in the makefile, it is common to make this a phony target named
2714 @samp{all} and give it, as prerequisites, all the individual programs. For
2718 all : prog1 prog2 prog3
2721 prog1 : prog1.o utils.o
2722 cc -o prog1 prog1.o utils.o
2727 prog3 : prog3.o sort.o utils.o
2728 cc -o prog3 prog3.o sort.o utils.o
2732 Now you can say just @samp{make} to remake all three programs, or
2733 specify as arguments the ones to remake (as in @samp{make prog1
2734 prog3}). Phoniness is not inherited: the prerequisites of a phony
2735 target are not themselves phony, unless explicitly declared to be so.
2737 When one phony target is a prerequisite of another, it serves as a subroutine
2738 of the other. For example, here @samp{make cleanall} will delete the
2739 object files, the difference files, and the file @file{program}:
2742 .PHONY: cleanall cleanobj cleandiff
2744 cleanall : cleanobj cleandiff
2754 @node Force Targets, Empty Targets, Phony Targets, Rules
2755 @section Rules without Commands or Prerequisites
2756 @cindex force targets
2757 @cindex targets, force
2758 @cindex @code{FORCE}
2759 @cindex rule, no commands or prerequisites
2761 If a rule has no prerequisites or commands, and the target of the rule
2762 is a nonexistent file, then @code{make} imagines this target to have
2763 been updated whenever its rule is run. This implies that all targets
2764 depending on this one will always have their commands run.
2766 An example will illustrate this:
2776 Here the target @samp{FORCE} satisfies the special conditions, so the
2777 target @file{clean} that depends on it is forced to run its commands.
2778 There is nothing special about the name @samp{FORCE}, but that is one name
2779 commonly used this way.
2781 As you can see, using @samp{FORCE} this way has the same results as using
2782 @samp{.PHONY: clean}.
2784 Using @samp{.PHONY} is more explicit and more efficient. However,
2785 other versions of @code{make} do not support @samp{.PHONY}; thus
2786 @samp{FORCE} appears in many makefiles. @xref{Phony Targets}.
2788 @node Empty Targets, Special Targets, Force Targets, Rules
2789 @section Empty Target Files to Record Events
2790 @cindex empty targets
2791 @cindex targets, empty
2792 @cindex recording events with empty targets
2794 The @dfn{empty target} is a variant of the phony target; it is used to hold
2795 commands for an action that you request explicitly from time to time.
2796 Unlike a phony target, this target file can really exist; but the file's
2797 contents do not matter, and usually are empty.
2799 The purpose of the empty target file is to record, with its
2800 last-modification time, when the rule's commands were last executed. It
2801 does so because one of the commands is a @code{touch} command to update the
2804 The empty target file should have some prerequisites (otherwise it
2805 doesn't make sense). When you ask to remake the empty target, the
2806 commands are executed if any prerequisite is more recent than the target;
2807 in other words, if a prerequisite has changed since the last time you
2808 remade the target. Here is an example:
2815 @cindex @code{print} target
2816 @cindex @code{lpr} (shell command)
2817 @cindex @code{touch} (shell command)
2820 With this rule, @samp{make print} will execute the @code{lpr} command if
2821 either source file has changed since the last @samp{make print}. The
2822 automatic variable @samp{$?} is used to print only those files that have
2823 changed (@pxref{Automatic Variables}).
2825 @node Special Targets, Multiple Targets, Empty Targets, Rules
2826 @section Special Built-in Target Names
2827 @cindex special targets
2828 @cindex built-in special targets
2829 @cindex targets, built-in special
2831 Certain names have special meanings if they appear as targets.
2837 The prerequisites of the special target @code{.PHONY} are considered to
2838 be phony targets. When it is time to consider such a target,
2839 @code{make} will run its commands unconditionally, regardless of
2840 whether a file with that name exists or what its last-modification
2841 time is. @xref{Phony Targets, ,Phony Targets}.
2846 The prerequisites of the special target @code{.SUFFIXES} are the list
2847 of suffixes to be used in checking for suffix rules.
2848 @xref{Suffix Rules, , Old-Fashioned Suffix Rules}.
2853 The commands specified for @code{.DEFAULT} are used for any target for
2854 which no rules are found (either explicit rules or implicit rules).
2855 @xref{Last Resort}. If @code{.DEFAULT} commands are specified, every
2856 file mentioned as a prerequisite, but not as a target in a rule, will have
2857 these commands executed on its behalf. @xref{Implicit Rule Search,
2858 ,Implicit Rule Search Algorithm}.
2862 @cindex precious targets
2863 @cindex preserving with @code{.PRECIOUS}
2865 The targets which @code{.PRECIOUS} depends on are given the following
2866 special treatment: if @code{make} is killed or interrupted during the
2867 execution of their commands, the target is not deleted.
2868 @xref{Interrupts, ,Interrupting or Killing @code{make}}. Also, if the
2869 target is an intermediate file, it will not be deleted after it is no
2870 longer needed, as is normally done. @xref{Chained Rules, ,Chains of
2871 Implicit Rules}. In this latter respect it overlaps with the
2872 @code{.SECONDARY} special target.
2874 You can also list the target pattern of an implicit rule (such as
2875 @samp{%.o}) as a prerequisite file of the special target @code{.PRECIOUS}
2876 to preserve intermediate files created by rules whose target patterns
2877 match that file's name.
2879 @findex .INTERMEDIATE
2881 @cindex intermediate targets, explicit
2883 The targets which @code{.INTERMEDIATE} depends on are treated as
2884 intermediate files. @xref{Chained Rules, ,Chains of Implicit Rules}.
2885 @code{.INTERMEDIATE} with no prerequisites has no effect.
2889 @cindex secondary targets
2890 @cindex preserving with @code{.SECONDARY}
2892 The targets which @code{.SECONDARY} depends on are treated as
2893 intermediate files, except that they are never automatically deleted.
2894 @xref{Chained Rules, ,Chains of Implicit Rules}.
2896 @code{.SECONDARY} with no prerequisites causes all targets to be treated
2897 as secondary (i.e., no target is removed because it is considered
2900 @findex .SECONDEXPANSION
2901 @item .SECONDEXPANSION
2903 If @code{.SECONDEXPANSION} is mentioned as a target anywhere in the
2904 makefile, then all prerequisite lists defined @emph{after} it appears
2905 will be expanded a second time after all makefiles have been read in.
2906 @xref{Secondary Expansion, ,Secondary Expansion}.
2908 The prerequisites of the special target @code{.SUFFIXES} are the list
2909 of suffixes to be used in checking for suffix rules.
2910 @xref{Suffix Rules, , Old-Fashioned Suffix Rules}.
2912 @findex .DELETE_ON_ERROR
2913 @item .DELETE_ON_ERROR
2914 @cindex removing targets on failure
2916 If @code{.DELETE_ON_ERROR} is mentioned as a target anywhere in the
2917 makefile, then @code{make} will delete the target of a rule if it has
2918 changed and its commands exit with a nonzero exit status, just as it
2919 does when it receives a signal. @xref{Errors, ,Errors in Commands}.
2924 If you specify prerequisites for @code{.IGNORE}, then @code{make} will
2925 ignore errors in execution of the commands run for those particular
2926 files. The commands for @code{.IGNORE} are not meaningful.
2928 If mentioned as a target with no prerequisites, @code{.IGNORE} says to
2929 ignore errors in execution of commands for all files. This usage of
2930 @samp{.IGNORE} is supported only for historical compatibility. Since
2931 this affects every command in the makefile, it is not very useful; we
2932 recommend you use the more selective ways to ignore errors in specific
2933 commands. @xref{Errors, ,Errors in Commands}.
2935 @findex .LOW_RESOLUTION_TIME
2936 @item .LOW_RESOLUTION_TIME
2938 If you specify prerequisites for @code{.LOW_RESOLUTION_TIME},
2939 @command{make} assumes that these files are created by commands that
2940 generate low resolution time stamps. The commands for
2941 @code{.LOW_RESOLUTION_TIME} are not meaningful.
2943 The high resolution file time stamps of many modern hosts lessen the
2944 chance of @command{make} incorrectly concluding that a file is up to
2945 date. Unfortunately, these hosts provide no way to set a high
2946 resolution file time stamp, so commands like @samp{cp -p} that
2947 explicitly set a file's time stamp must discard its subsecond part. If
2948 a file is created by such a command, you should list it as a
2949 prerequisite of @code{.LOW_RESOLUTION_TIME} so that @command{make} does
2950 not mistakenly conclude that the file is out of date. For example:
2954 .LOW_RESOLUTION_TIME: dst
2960 Since @samp{cp -p} discards the subsecond part of @file{src}'s time
2961 stamp, @file{dst} is typically slightly older than @file{src} even when
2962 it is up to date. The @code{.LOW_RESOLUTION_TIME} line causes
2963 @command{make} to consider @file{dst} to be up to date if its time stamp
2964 is at the start of the same second that @file{src}'s time stamp is in.
2966 Due to a limitation of the archive format, archive member time stamps
2967 are always low resolution. You need not list archive members as
2968 prerequisites of @code{.LOW_RESOLUTION_TIME}, as @command{make} does this
2974 If you specify prerequisites for @code{.SILENT}, then @code{make} will
2975 not print the commands to remake those particular files before executing
2976 them. The commands for @code{.SILENT} are not meaningful.
2978 If mentioned as a target with no prerequisites, @code{.SILENT} says not
2979 to print any commands before executing them. This usage of
2980 @samp{.SILENT} is supported only for historical compatibility. We
2981 recommend you use the more selective ways to silence specific commands.
2982 @xref{Echoing, ,Command Echoing}. If you want to silence all commands
2983 for a particular run of @code{make}, use the @samp{-s} or
2984 @w{@samp{--silent}} option (@pxref{Options Summary}).
2986 @findex .EXPORT_ALL_VARIABLES
2987 @item .EXPORT_ALL_VARIABLES
2989 Simply by being mentioned as a target, this tells @code{make} to
2990 export all variables to child processes by default.
2991 @xref{Variables/Recursion, ,Communicating Variables to a
2994 @findex .NOTPARALLEL
2996 @cindex parallel execution, overriding
2998 If @code{.NOTPARALLEL} is mentioned as a target, then this invocation of
2999 @code{make} will be run serially, even if the @samp{-j} option is
3000 given. Any recursively invoked @code{make} command will still be run in
3001 parallel (unless its makefile contains this target). Any prerequisites
3002 on this target are ignored.
3005 Any defined implicit rule suffix also counts as a special target if it
3006 appears as a target, and so does the concatenation of two suffixes, such
3007 as @samp{.c.o}. These targets are suffix rules, an obsolete way of
3008 defining implicit rules (but a way still widely used). In principle, any
3009 target name could be special in this way if you break it in two and add
3010 both pieces to the suffix list. In practice, suffixes normally begin with
3011 @samp{.}, so these special target names also begin with @samp{.}.
3012 @xref{Suffix Rules, ,Old-Fashioned Suffix Rules}.
3014 @node Multiple Targets, Multiple Rules, Special Targets, Rules
3015 @section Multiple Targets in a Rule
3016 @cindex multiple targets
3017 @cindex several targets in a rule
3018 @cindex targets, multiple
3019 @cindex rule, with multiple targets
3021 A rule with multiple targets is equivalent to writing many rules, each with
3022 one target, and all identical aside from that. The same commands apply to
3023 all the targets, but their effects may vary because you can substitute the
3024 actual target name into the command using @samp{$@@}. The rule contributes
3025 the same prerequisites to all the targets also.
3027 This is useful in two cases.
3031 You want just prerequisites, no commands. For example:
3034 kbd.o command.o files.o: command.h
3038 gives an additional prerequisite to each of the three object files
3042 Similar commands work for all the targets. The commands do not need
3043 to be absolutely identical, since the automatic variable @samp{$@@}
3044 can be used to substitute the particular target to be remade into the
3045 commands (@pxref{Automatic Variables}). For example:
3049 bigoutput littleoutput : text.g
3050 generate text.g -$(subst output,,$@@) > $@@
3060 generate text.g -big > bigoutput
3061 littleoutput : text.g
3062 generate text.g -little > littleoutput
3066 Here we assume the hypothetical program @code{generate} makes two
3067 types of output, one if given @samp{-big} and one if given
3069 @xref{Text Functions, ,Functions for String Substitution and Analysis},
3070 for an explanation of the @code{subst} function.
3073 Suppose you would like to vary the prerequisites according to the target,
3074 much as the variable @samp{$@@} allows you to vary the commands.
3075 You cannot do this with multiple targets in an ordinary rule, but you can
3076 do it with a @dfn{static pattern rule}.
3077 @xref{Static Pattern, ,Static Pattern Rules}.
3079 @node Multiple Rules, Static Pattern, Multiple Targets, Rules
3080 @section Multiple Rules for One Target
3081 @cindex multiple rules for one target
3082 @cindex several rules for one target
3083 @cindex rule, multiple for one target
3084 @cindex target, multiple rules for one
3086 One file can be the target of several rules. All the prerequisites
3087 mentioned in all the rules are merged into one list of prerequisites for
3088 the target. If the target is older than any prerequisite from any rule,
3089 the commands are executed.
3091 There can only be one set of commands to be executed for a file. If
3092 more than one rule gives commands for the same file, @code{make} uses
3093 the last set given and prints an error message. (As a special case,
3094 if the file's name begins with a dot, no error message is printed.
3095 This odd behavior is only for compatibility with other implementations
3096 of @code{make}... you should avoid using it). Occasionally it is
3097 useful to have the same target invoke multiple commands which are
3098 defined in different parts of your makefile; you can use
3099 @dfn{double-colon rules} (@pxref{Double-Colon}) for this.
3101 An extra rule with just prerequisites can be used to give a few extra
3102 prerequisites to many files at once. For example, makefiles often
3103 have a variable, such as @code{objects}, containing a list of all the
3104 compiler output files in the system being made. An easy way to say
3105 that all of them must be recompiled if @file{config.h} changes is to
3106 write the following:
3109 objects = foo.o bar.o
3111 bar.o : defs.h test.h
3112 $(objects) : config.h
3115 This could be inserted or taken out without changing the rules that really
3116 specify how to make the object files, making it a convenient form to use if
3117 you wish to add the additional prerequisite intermittently.
3119 Another wrinkle is that the additional prerequisites could be specified with
3120 a variable that you set with a command argument to @code{make}
3121 (@pxref{Overriding, ,Overriding Variables}). For example,
3126 $(objects) : $(extradeps)
3131 means that the command @samp{make extradeps=foo.h} will consider
3132 @file{foo.h} as a prerequisite of each object file, but plain @samp{make}
3135 If none of the explicit rules for a target has commands, then @code{make}
3136 searches for an applicable implicit rule to find some commands
3137 @pxref{Implicit Rules, ,Using Implicit Rules}).
3139 @node Static Pattern, Double-Colon, Multiple Rules, Rules
3140 @section Static Pattern Rules
3141 @cindex static pattern rule
3142 @cindex rule, static pattern
3143 @cindex pattern rules, static (not implicit)
3144 @cindex varying prerequisites
3145 @cindex prerequisites, varying (static pattern)
3147 @dfn{Static pattern rules} are rules which specify multiple targets and
3148 construct the prerequisite names for each target based on the target name.
3149 They are more general than ordinary rules with multiple targets because the
3150 targets do not have to have identical prerequisites. Their prerequisites must
3151 be @emph{analogous}, but not necessarily @emph{identical}.
3154 * Static Usage:: The syntax of static pattern rules.
3155 * Static versus Implicit:: When are they better than implicit rules?
3158 @node Static Usage, Static versus Implicit, Static Pattern, Static Pattern
3159 @subsection Syntax of Static Pattern Rules
3160 @cindex static pattern rule, syntax of
3161 @cindex pattern rules, static, syntax of
3163 Here is the syntax of a static pattern rule:
3166 @var{targets} @dots{}: @var{target-pattern}: @var{prereq-patterns} @dots{}
3172 The @var{targets} list specifies the targets that the rule applies to.
3173 The targets can contain wildcard characters, just like the targets of
3174 ordinary rules (@pxref{Wildcards, ,Using Wildcard Characters in File
3177 @cindex target pattern, static (not implicit)
3179 The @var{target-pattern} and @var{prereq-patterns} say how to compute the
3180 prerequisites of each target. Each target is matched against the
3181 @var{target-pattern} to extract a part of the target name, called the
3182 @dfn{stem}. This stem is substituted into each of the @var{prereq-patterns}
3183 to make the prerequisite names (one from each @var{prereq-pattern}).
3185 Each pattern normally contains the character @samp{%} just once. When the
3186 @var{target-pattern} matches a target, the @samp{%} can match any part of
3187 the target name; this part is called the @dfn{stem}. The rest of the
3188 pattern must match exactly. For example, the target @file{foo.o} matches
3189 the pattern @samp{%.o}, with @samp{foo} as the stem. The targets
3190 @file{foo.c} and @file{foo.out} do not match that pattern.@refill
3192 @cindex prerequisite pattern, static (not implicit)
3193 The prerequisite names for each target are made by substituting the stem
3194 for the @samp{%} in each prerequisite pattern. For example, if one
3195 prerequisite pattern is @file{%.c}, then substitution of the stem
3196 @samp{foo} gives the prerequisite name @file{foo.c}. It is legitimate
3197 to write a prerequisite pattern that does not contain @samp{%}; then this
3198 prerequisite is the same for all targets.
3200 @cindex @code{%}, quoting in static pattern
3201 @cindex @code{%}, quoting with @code{\} (backslash)
3202 @cindex @code{\} (backslash), to quote @code{%}
3203 @cindex backslash (@code{\}), to quote @code{%}
3204 @cindex quoting @code{%}, in static pattern
3205 @samp{%} characters in pattern rules can be quoted with preceding
3206 backslashes (@samp{\}). Backslashes that would otherwise quote @samp{%}
3207 characters can be quoted with more backslashes. Backslashes that quote
3208 @samp{%} characters or other backslashes are removed from the pattern
3209 before it is compared to file names or has a stem substituted into it.
3210 Backslashes that are not in danger of quoting @samp{%} characters go
3211 unmolested. For example, the pattern @file{the\%weird\\%pattern\\} has
3212 @samp{the%weird\} preceding the operative @samp{%} character, and
3213 @samp{pattern\\} following it. The final two backslashes are left alone
3214 because they cannot affect any @samp{%} character.@refill
3216 Here is an example, which compiles each of @file{foo.o} and @file{bar.o}
3217 from the corresponding @file{.c} file:
3221 objects = foo.o bar.o
3225 $(objects): %.o: %.c
3226 $(CC) -c $(CFLAGS) $< -o $@@
3231 Here @samp{$<} is the automatic variable that holds the name of the
3232 prerequisite and @samp{$@@} is the automatic variable that holds the name
3233 of the target; see @ref{Automatic Variables}.
3235 Each target specified must match the target pattern; a warning is issued
3236 for each target that does not. If you have a list of files, only some of
3237 which will match the pattern, you can use the @code{filter} function to
3238 remove nonmatching file names (@pxref{Text Functions, ,Functions for String Substitution and Analysis}):
3241 files = foo.elc bar.o lose.o
3243 $(filter %.o,$(files)): %.o: %.c
3244 $(CC) -c $(CFLAGS) $< -o $@@
3245 $(filter %.elc,$(files)): %.elc: %.el
3246 emacs -f batch-byte-compile $<
3250 In this example the result of @samp{$(filter %.o,$(files))} is
3251 @file{bar.o lose.o}, and the first static pattern rule causes each of
3252 these object files to be updated by compiling the corresponding C source
3253 file. The result of @w{@samp{$(filter %.elc,$(files))}} is
3254 @file{foo.elc}, so that file is made from @file{foo.el}.@refill
3256 Another example shows how to use @code{$*} in static pattern rules:
3257 @vindex $*@r{, and static pattern}
3261 bigoutput littleoutput : %output : text.g
3262 generate text.g -$* > $@@
3267 When the @code{generate} command is run, @code{$*} will expand to the
3268 stem, either @samp{big} or @samp{little}.
3270 @node Static versus Implicit, , Static Usage, Static Pattern
3271 @subsection Static Pattern Rules versus Implicit Rules
3272 @cindex rule, static pattern versus implicit
3273 @cindex static pattern rule, versus implicit
3275 A static pattern rule has much in common with an implicit rule defined as a
3276 pattern rule (@pxref{Pattern Rules, ,Defining and Redefining Pattern Rules}).
3277 Both have a pattern for the target and patterns for constructing the
3278 names of prerequisites. The difference is in how @code{make} decides
3279 @emph{when} the rule applies.
3281 An implicit rule @emph{can} apply to any target that matches its pattern,
3282 but it @emph{does} apply only when the target has no commands otherwise
3283 specified, and only when the prerequisites can be found. If more than one
3284 implicit rule appears applicable, only one applies; the choice depends on
3287 By contrast, a static pattern rule applies to the precise list of targets
3288 that you specify in the rule. It cannot apply to any other target and it
3289 invariably does apply to each of the targets specified. If two conflicting
3290 rules apply, and both have commands, that's an error.
3292 The static pattern rule can be better than an implicit rule for these
3297 You may wish to override the usual implicit rule for a few
3298 files whose names cannot be categorized syntactically but
3299 can be given in an explicit list.
3302 If you cannot be sure of the precise contents of the directories
3303 you are using, you may not be sure which other irrelevant files
3304 might lead @code{make} to use the wrong implicit rule. The choice
3305 might depend on the order in which the implicit rule search is done.
3306 With static pattern rules, there is no uncertainty: each rule applies
3307 to precisely the targets specified.
3310 @node Double-Colon, Automatic Prerequisites, Static Pattern, Rules
3311 @section Double-Colon Rules
3312 @cindex double-colon rules
3313 @cindex rule, double-colon (@code{::})
3314 @cindex multiple rules for one target (@code{::})
3315 @cindex @code{::} rules (double-colon)
3317 @dfn{Double-colon} rules are rules written with @samp{::} instead of
3318 @samp{:} after the target names. They are handled differently from
3319 ordinary rules when the same target appears in more than one rule.
3321 When a target appears in multiple rules, all the rules must be the same
3322 type: all ordinary, or all double-colon. If they are double-colon, each
3323 of them is independent of the others. Each double-colon rule's commands
3324 are executed if the target is older than any prerequisites of that rule.
3325 If there are no prerequisites for that rule, its commands are always
3326 executed (even if the target already exists). This can result in
3327 executing none, any, or all of the double-colon rules.
3329 Double-colon rules with the same target are in fact completely separate
3330 from one another. Each double-colon rule is processed individually, just
3331 as rules with different targets are processed.
3333 The double-colon rules for a target are executed in the order they appear
3334 in the makefile. However, the cases where double-colon rules really make
3335 sense are those where the order of executing the commands would not matter.
3337 Double-colon rules are somewhat obscure and not often very useful; they
3338 provide a mechanism for cases in which the method used to update a target
3339 differs depending on which prerequisite files caused the update, and such
3342 Each double-colon rule should specify commands; if it does not, an
3343 implicit rule will be used if one applies.
3344 @xref{Implicit Rules, ,Using Implicit Rules}.
3346 @node Automatic Prerequisites, , Double-Colon, Rules
3347 @section Generating Prerequisites Automatically
3348 @cindex prerequisites, automatic generation
3349 @cindex automatic generation of prerequisites
3350 @cindex generating prerequisites automatically
3352 In the makefile for a program, many of the rules you need to write often
3353 say only that some object file depends on some header
3354 file. For example, if @file{main.c} uses @file{defs.h} via an
3355 @code{#include}, you would write:
3362 You need this rule so that @code{make} knows that it must remake
3363 @file{main.o} whenever @file{defs.h} changes. You can see that for a
3364 large program you would have to write dozens of such rules in your
3365 makefile. And, you must always be very careful to update the makefile
3366 every time you add or remove an @code{#include}.
3367 @cindex @code{#include}
3369 @cindex @code{-M} (to compiler)
3370 To avoid this hassle, most modern C compilers can write these rules for
3371 you, by looking at the @code{#include} lines in the source files.
3372 Usually this is done with the @samp{-M} option to the compiler.
3373 For example, the command:
3380 generates the output:
3383 main.o : main.c defs.h
3387 Thus you no longer have to write all those rules yourself.
3388 The compiler will do it for you.
3390 Note that such a prerequisite constitutes mentioning @file{main.o} in a
3391 makefile, so it can never be considered an intermediate file by implicit
3392 rule search. This means that @code{make} won't ever remove the file
3393 after using it; @pxref{Chained Rules, ,Chains of Implicit Rules}.
3395 @cindex @code{make depend}
3396 With old @code{make} programs, it was traditional practice to use this
3397 compiler feature to generate prerequisites on demand with a command like
3398 @samp{make depend}. That command would create a file @file{depend}
3399 containing all the automatically-generated prerequisites; then the
3400 makefile could use @code{include} to read them in (@pxref{Include}).
3402 In GNU @code{make}, the feature of remaking makefiles makes this
3403 practice obsolete---you need never tell @code{make} explicitly to
3404 regenerate the prerequisites, because it always regenerates any makefile
3405 that is out of date. @xref{Remaking Makefiles}.
3407 The practice we recommend for automatic prerequisite generation is to have
3408 one makefile corresponding to each source file. For each source file
3409 @file{@var{name}.c} there is a makefile @file{@var{name}.d} which lists
3410 what files the object file @file{@var{name}.o} depends on. That way
3411 only the source files that have changed need to be rescanned to produce
3412 the new prerequisites.
3414 Here is the pattern rule to generate a file of prerequisites (i.e., a makefile)
3415 called @file{@var{name}.d} from a C source file called @file{@var{name}.c}:
3420 @@set -e; rm -f $@@; \
3421 $(CC) -M $(CPPFLAGS) $< > $@@.$$$$; \
3422 sed 's,\($*\)\.o[ :]*,\1.o $@@ : ,g' < $@@.$$$$ > $@@; \
3428 @xref{Pattern Rules}, for information on defining pattern rules. The
3429 @samp{-e} flag to the shell causes it to exit immediately if the
3430 @code{$(CC)} command (or any other command) fails (exits with a
3432 @cindex @code{-e} (shell flag)
3434 @cindex @code{-MM} (to GNU compiler)
3435 With the GNU C compiler, you may wish to use the @samp{-MM} flag instead
3436 of @samp{-M}. This omits prerequisites on system header files.
3437 @xref{Preprocessor Options, , Options Controlling the Preprocessor,
3438 gcc.info, Using GNU CC}, for details.
3440 @cindex @code{sed} (shell command)
3441 The purpose of the @code{sed} command is to translate (for example):
3444 main.o : main.c defs.h
3451 main.o main.d : main.c defs.h
3456 This makes each @samp{.d} file depend on all the source and header files
3457 that the corresponding @samp{.o} file depends on. @code{make} then
3458 knows it must regenerate the prerequisites whenever any of the source or
3459 header files changes.
3461 Once you've defined the rule to remake the @samp{.d} files,
3462 you then use the @code{include} directive to read them all in.
3463 @xref{Include}. For example:
3467 sources = foo.c bar.c
3469 include $(sources:.c=.d)
3474 (This example uses a substitution variable reference to translate the
3475 list of source files @samp{foo.c bar.c} into a list of prerequisite
3476 makefiles, @samp{foo.d bar.d}. @xref{Substitution Refs}, for full
3477 information on substitution references.) Since the @samp{.d} files are
3478 makefiles like any others, @code{make} will remake them as necessary
3479 with no further work from you. @xref{Remaking Makefiles}.
3481 Note that the @samp{.d} files contain target definitions; you should
3482 be sure to place the @code{include} directive @emph{after} the first,
3483 default goal in your makefiles or run the risk of having a random
3484 object file become the default goal.
3485 @xref{How Make Works}.
3487 @node Commands, Using Variables, Rules, Top
3488 @chapter Writing the Commands in Rules
3489 @cindex commands, how to write
3490 @cindex rule commands
3491 @cindex writing rule commands
3493 The commands of a rule consist of one or more shell command lines to
3494 be executed, one at a time, in the order they appear. Typically, the
3495 result of executing these commands is that the target of the rule is
3498 Users use many different shell programs, but commands in makefiles are
3499 always interpreted by @file{/bin/sh} unless the makefile specifies
3500 otherwise. @xref{Execution, ,Command Execution}.
3503 * Command Syntax:: Command syntax features and pitfalls.
3504 * Echoing:: How to control when commands are echoed.
3505 * Execution:: How commands are executed.
3506 * Parallel:: How commands can be executed in parallel.
3507 * Errors:: What happens after a command execution error.
3508 * Interrupts:: What happens when a command is interrupted.
3509 * Recursion:: Invoking @code{make} from makefiles.
3510 * Sequences:: Defining canned sequences of commands.
3511 * Empty Commands:: Defining useful, do-nothing commands.
3514 @node Command Syntax, Echoing, Commands, Commands
3515 @section Command Syntax
3516 @cindex command syntax
3517 @cindex syntax of commands
3519 Makefiles have the unusual property that there are really two distinct
3520 syntaxes in one file. Most of the makefile uses @code{make} syntax
3521 (@pxref{Makefiles, ,Writing Makefiles}). However, commands are meant to be
3522 interpreted by the shell and so they are written using shell syntax.
3523 The @code{make} program does not try to understand shell syntax: it
3524 performs only a very few specific translations on the content of the
3525 command before handing it to the shell.
3527 Each command line must start with a tab, except that the first command
3528 line may be attached to the target-and-prerequisites line with a
3529 semicolon in between. @emph{Any} line in the makefile that begins
3530 with a tab and appears in a ``rule context'' (that is, after a rule
3531 has been started until another rule or variable definition) will be
3532 considered a command line for that rule. Blank lines and lines of
3533 just comments may appear among the command lines; they are ignored.
3535 Some consequences of these rules include:
3539 A blank line that begins with a tab is not blank: it's an empty
3540 command (@pxref{Empty Commands}).
3542 @cindex comments, in commands
3543 @cindex commands, comments in
3544 @cindex @code{#} (comments), in commands
3546 A comment in a command line is not a @code{make} comment; it will be
3547 passed to the shell as-is. Whether the shell treats it as a comment
3548 or not depends on your shell.
3551 A variable definition in a ``rule context'' which is indented by a tab
3552 as the first character on the line, will be considered a command line,
3553 not a @code{make} variable definition, and passed to the shell.
3556 A conditional expression (@code{ifdef}, @code{ifeq},
3557 etc. @pxref{Conditional Syntax, ,Syntax of Conditionals}) in a ``rule
3558 context'' which is indented by a tab as the first character on the
3559 line, will be considered a command line and be passed to the shell.
3564 * Splitting Lines:: Breaking long command lines for readability.
3565 * Variables in Commands:: Using @code{make} variables in commands.
3568 @node Splitting Lines, Variables in Commands, Command Syntax, Command Syntax
3569 @subsection Splitting Command Lines
3570 @cindex commands, splitting
3571 @cindex splitting commands
3572 @cindex commands, backslash (@code{\}) in
3573 @cindex commands, quoting newlines in
3574 @cindex backslash (@code{\}), in commands
3575 @cindex @code{\} (backslash), in commands
3576 @cindex quoting newline, in commands
3577 @cindex newline, quoting, in commands
3579 One of the few ways in which @code{make} does interpret command lines
3580 is checking for a backslash just before the newline. As in normal
3581 makefile syntax, a single command can be split into multiple lines in
3582 the makefile by placing a backslash before each newline. A sequence
3583 of lines like this is considered a single command, and one instance of
3584 the shell will be invoked to run it.
3586 However, in contrast to how they are treated in other places in a
3587 makefile, backslash-newline pairs are @emph{not} removed from the
3588 command. Both the backslash and the newline characters are preserved
3589 and passed to the shell. How the backslash-newline is interpreted
3590 depends on your shell. If the first character of the next line
3591 after the backslash-newline is a tab, then that tab (and only that
3592 tab) is removed. Whitespace is never added to the command.
3594 For example, this makefile:
3611 consists of four separate shell commands where the output is:
3622 As a more complex example, this makefile:
3626 all : ; @@echo 'hello \
3627 world' ; echo "hello \
3633 will run one shell with a command script of:
3638 world' ; echo "hello \
3644 which, according to shell quoting rules, will yield the following output:
3655 Notice how the backslash/newline pair was removed inside the string quoted
3656 with double quotes (@code{"..."}), but not from the string quoted with single
3657 quotes (@code{'...'}). This is the way the default shell (@file{/bin/sh})
3658 handles backslash/newline pairs. If you specify a different shell in your
3659 makefiles it may treat them differently.
3661 Sometimes you want to split a long line inside of single quotes, but
3662 you don't want the backslash-newline to appear in the quoted content.
3663 This is often the case when passing scripts to languages such as Perl,
3664 where extraneous backslashes inside the script can change its meaning
3665 or even be a syntax error. One simple way of handling this is to
3666 place the quoted string, or even the entire command, into a
3667 @code{make} variable then use the variable in the command. In this
3668 situation the newline quoting rules for makefiles will be used, and
3669 the backslash-newline will be removed. If we rewrite our example
3670 above using this method:
3677 all : ; @@echo $(HELLO)
3682 we will get output like this:
3690 If you like, you can also use target-specific variables
3691 (@pxref{Target-specific, ,Target-specific Variable Values}) to obtain
3692 a tighter correspondence between the variable and the command that
3695 @node Variables in Commands, , Splitting Lines, Command Syntax
3696 @subsection Using Variables in Commands
3697 @cindex variable references in commands
3698 @cindex commands, using variables in
3700 The other way in which @code{make} processes commands is by expanding
3701 any variable references in them (@pxref{Reference,Basics of Variable
3702 References}). This occurs after make has finished reading all the
3703 makefiles and the target is determined to be out of date; so, the
3704 commands for targets which are not rebuilt are never expanded.
3706 Variable and function references in commands have identical syntax and
3707 semantics to references elsewhere in the makefile. They also have the
3708 same quoting rules: if you want a dollar sign to appear in your
3709 command, you must double it (@samp{$$}). For shells like the default
3710 shell, that use dollar signs to introduce variables, it's important to
3711 keep clear in your mind whether the variable you want to reference is
3712 a @code{make} variable (use a single dollar sign) or a shell variable
3713 (use two dollar signs). For example:
3717 LIST = one two three
3719 for i in $(LIST); do \
3726 results in the following command being passed to the shell:
3730 for i in one two three; do \
3737 which generates the expected result:
3747 @node Echoing, Execution, Command Syntax, Commands
3748 @section Command Echoing
3749 @cindex echoing of commands
3750 @cindex silent operation
3751 @cindex @code{@@} (in commands)
3752 @cindex commands, echoing
3753 @cindex printing of commands
3755 Normally @code{make} prints each command line before it is executed.
3756 We call this @dfn{echoing} because it gives the appearance that you
3757 are typing the commands yourself.
3759 When a line starts with @samp{@@}, the echoing of that line is suppressed.
3760 The @samp{@@} is discarded before the command is passed to the shell.
3761 Typically you would use this for a command whose only effect is to print
3762 something, such as an @code{echo} command to indicate progress through
3766 @@echo About to make distribution files
3770 @cindex @code{--just-print}
3771 @cindex @code{--dry-run}
3772 @cindex @code{--recon}
3773 When @code{make} is given the flag @samp{-n} or @samp{--just-print}
3774 it only echoes commands, it won't execute them. @xref{Options Summary,
3775 ,Summary of Options}. In this case and only this case, even the
3776 commands starting with @samp{@@} are printed. This flag is useful for
3777 finding out which commands @code{make} thinks are necessary without
3778 actually doing them.
3781 @cindex @code{--silent}
3782 @cindex @code{--quiet}
3784 The @samp{-s} or @samp{--silent}
3785 flag to @code{make} prevents all echoing, as if all commands
3786 started with @samp{@@}. A rule in the makefile for the special target
3787 @code{.SILENT} without prerequisites has the same effect
3788 (@pxref{Special Targets, ,Special Built-in Target Names}).
3789 @code{.SILENT} is essentially obsolete since @samp{@@} is more flexible.@refill
3791 @node Execution, Parallel, Echoing, Commands
3792 @section Command Execution
3793 @cindex commands, execution
3794 @cindex execution, of commands
3795 @cindex shell command, execution
3796 @vindex @code{SHELL} @r{(command execution)}
3798 When it is time to execute commands to update a target, they are
3799 executed by invoking a new subshell for each command line. (In
3800 practice, @code{make} may take shortcuts that do not affect the
3803 @cindex @code{cd} (shell command)
3804 @cindex shell variables, setting in commands
3805 @cindex commands setting shell variables
3806 @strong{Please note:} this implies that setting shell variables and
3807 invoking shell commands such as @code{cd} that set a context local to
3808 each process will not affect the following command lines.@footnote{On
3809 MS-DOS, the value of current working directory is @strong{global}, so
3810 changing it @emph{will} affect the following command lines on those
3811 systems.} If you want to use @code{cd} to affect the next statement,
3812 put both statements in a single command line. Then @code{make} will
3813 invoke one shell to run the entire line, and the shell will execute
3814 the statements in sequence. For example:
3818 cd $(@@D) && gobble $(@@F) > ../$@@
3822 Here we use the shell AND operator (@code{&&}) so that if the
3823 @code{cd} command fails, the script will fail without trying to invoke
3824 the @code{gobble} command in the wrong directory, which could cause
3825 problems (in this case it would certainly cause @file{../foo} to be
3826 truncated, at least).
3829 * Choosing the Shell:: How @code{make} chooses the shell used
3833 @node Choosing the Shell, , Execution, Execution
3834 @subsection Choosing the Shell
3835 @cindex shell, choosing the
3836 @cindex @code{SHELL}, value of
3839 The program used as the shell is taken from the variable @code{SHELL}.
3840 If this variable is not set in your makefile, the program
3841 @file{/bin/sh} is used as the shell.
3843 @cindex environment, @code{SHELL} in
3844 Unlike most variables, the variable @code{SHELL} is never set from the
3845 environment. This is because the @code{SHELL} environment variable is
3846 used to specify your personal choice of shell program for interactive
3847 use. It would be very bad for personal choices like this to affect the
3848 functioning of makefiles. @xref{Environment, ,Variables from the
3851 Furthermore, when you do set @code{SHELL} in your makefile that value
3852 is @emph{not} exported in the environment to commands that @code{make}
3853 invokes. Instead, the value inherited from the user's environment, if
3854 any, is exported. You can override this behavior by explicitly
3855 exporting @code{SHELL} (@pxref{Variables/Recursion, ,Communicating
3856 Variables to a Sub-@code{make}}), forcing it to be passed in the
3857 environment to commands.
3859 @vindex @code{MAKESHELL} @r{(MS-DOS alternative to @code{SHELL})}
3860 However, on MS-DOS and MS-Windows the value of @code{SHELL} in the
3861 environment @strong{is} used, since on those systems most users do not
3862 set this variable, and therefore it is most likely set specifically to
3863 be used by @code{make}. On MS-DOS, if the setting of @code{SHELL} is
3864 not suitable for @code{make}, you can set the variable
3865 @code{MAKESHELL} to the shell that @code{make} should use; if set it
3866 will be used as the shell instead of the value of @code{SHELL}.
3868 @subsubheading Choosing a Shell in DOS and Windows
3869 @cindex shell, in DOS and Windows
3870 @cindex DOS, choosing a shell in
3871 @cindex Windows, choosing a shell in
3873 Choosing a shell in MS-DOS and MS-Windows is much more complex than on
3877 On MS-DOS, if @code{SHELL} is not set, the value of the variable
3878 @code{COMSPEC} (which is always set) is used instead.
3880 @cindex @code{SHELL}, MS-DOS specifics
3881 The processing of lines that set the variable @code{SHELL} in Makefiles
3882 is different on MS-DOS. The stock shell, @file{command.com}, is
3883 ridiculously limited in its functionality and many users of @code{make}
3884 tend to install a replacement shell. Therefore, on MS-DOS, @code{make}
3885 examines the value of @code{SHELL}, and changes its behavior based on
3886 whether it points to a Unix-style or DOS-style shell. This allows
3887 reasonable functionality even if @code{SHELL} points to
3890 If @code{SHELL} points to a Unix-style shell, @code{make} on MS-DOS
3891 additionally checks whether that shell can indeed be found; if not, it
3892 ignores the line that sets @code{SHELL}. In MS-DOS, GNU @code{make}
3893 searches for the shell in the following places:
3897 In the precise place pointed to by the value of @code{SHELL}. For
3898 example, if the makefile specifies @samp{SHELL = /bin/sh}, @code{make}
3899 will look in the directory @file{/bin} on the current drive.
3902 In the current directory.
3905 In each of the directories in the @code{PATH} variable, in order.
3909 In every directory it examines, @code{make} will first look for the
3910 specific file (@file{sh} in the example above). If this is not found,
3911 it will also look in that directory for that file with one of the known
3912 extensions which identify executable files. For example @file{.exe},
3913 @file{.com}, @file{.bat}, @file{.btm}, @file{.sh}, and some others.
3915 If any of these attempts is successful, the value of @code{SHELL} will
3916 be set to the full pathname of the shell as found. However, if none of
3917 these is found, the value of @code{SHELL} will not be changed, and thus
3918 the line that sets it will be effectively ignored. This is so
3919 @code{make} will only support features specific to a Unix-style shell if
3920 such a shell is actually installed on the system where @code{make} runs.
3922 Note that this extended search for the shell is limited to the cases
3923 where @code{SHELL} is set from the Makefile; if it is set in the
3924 environment or command line, you are expected to set it to the full
3925 pathname of the shell, exactly as things are on Unix.
3927 The effect of the above DOS-specific processing is that a Makefile that
3928 contains @samp{SHELL = /bin/sh} (as many Unix makefiles do), will work
3929 on MS-DOS unaltered if you have e.g.@: @file{sh.exe} installed in some
3930 directory along your @code{PATH}.
3932 @node Parallel, Errors, Execution, Commands
3933 @section Parallel Execution
3934 @cindex commands, execution in parallel
3935 @cindex parallel execution
3936 @cindex execution, in parallel
3939 @cindex @code{--jobs}
3941 GNU @code{make} knows how to execute several commands at once.
3942 Normally, @code{make} will execute only one command at a time, waiting
3943 for it to finish before executing the next. However, the @samp{-j} or
3944 @samp{--jobs} option tells @code{make} to execute many commands
3945 simultaneously.@refill
3947 On MS-DOS, the @samp{-j} option has no effect, since that system doesn't
3948 support multi-processing.
3950 If the @samp{-j} option is followed by an integer, this is the number of
3951 commands to execute at once; this is called the number of @dfn{job slots}.
3952 If there is nothing looking like an integer after the @samp{-j} option,
3953 there is no limit on the number of job slots. The default number of job
3954 slots is one, which means serial execution (one thing at a time).
3956 One unpleasant consequence of running several commands simultaneously is
3957 that output generated by the commands appears whenever each command
3958 sends it, so messages from different commands may be interspersed.
3960 Another problem is that two processes cannot both take input from the
3961 same device; so to make sure that only one command tries to take input
3962 from the terminal at once, @code{make} will invalidate the standard
3963 input streams of all but one running command. This means that
3964 attempting to read from standard input will usually be a fatal error (a
3965 @samp{Broken pipe} signal) for most child processes if there are
3968 @cindex standard input
3970 It is unpredictable which command will have a valid standard input stream
3971 (which will come from the terminal, or wherever you redirect the standard
3972 input of @code{make}). The first command run will always get it first, and
3973 the first command started after that one finishes will get it next, and so
3976 We will change how this aspect of @code{make} works if we find a better
3977 alternative. In the mean time, you should not rely on any command using
3978 standard input at all if you are using the parallel execution feature; but
3979 if you are not using this feature, then standard input works normally in
3982 Finally, handling recursive @code{make} invocations raises issues. For
3983 more information on this, see
3984 @ref{Options/Recursion, ,Communicating Options to a Sub-@code{make}}.
3986 If a command fails (is killed by a signal or exits with a nonzero
3987 status), and errors are not ignored for that command
3988 (@pxref{Errors, ,Errors in Commands}),
3989 the remaining command lines to remake the same target will not be run.
3990 If a command fails and the @samp{-k} or @samp{--keep-going}
3991 option was not given
3992 (@pxref{Options Summary, ,Summary of Options}),
3993 @code{make} aborts execution. If make
3994 terminates for any reason (including a signal) with child processes
3995 running, it waits for them to finish before actually exiting.@refill
3997 @cindex load average
3998 @cindex limiting jobs based on load
3999 @cindex jobs, limiting based on load
4000 @cindex @code{-l} (load average)
4001 @cindex @code{--max-load}
4002 @cindex @code{--load-average}
4003 When the system is heavily loaded, you will probably want to run fewer jobs
4004 than when it is lightly loaded. You can use the @samp{-l} option to tell
4005 @code{make} to limit the number of jobs to run at once, based on the load
4006 average. The @samp{-l} or @samp{--max-load}
4007 option is followed by a floating-point number. For
4015 will not let @code{make} start more than one job if the load average is
4016 above 2.5. The @samp{-l} option with no following number removes the
4017 load limit, if one was given with a previous @samp{-l} option.@refill
4019 More precisely, when @code{make} goes to start up a job, and it already has
4020 at least one job running, it checks the current load average; if it is not
4021 lower than the limit given with @samp{-l}, @code{make} waits until the load
4022 average goes below that limit, or until all the other jobs finish.
4024 By default, there is no load limit.
4026 @node Errors, Interrupts, Parallel, Commands
4027 @section Errors in Commands
4028 @cindex errors (in commands)
4029 @cindex commands, errors in
4030 @cindex exit status (errors)
4032 After each shell command returns, @code{make} looks at its exit status.
4033 If the command completed successfully, the next command line is executed
4034 in a new shell; after the last command line is finished, the rule is
4037 If there is an error (the exit status is nonzero), @code{make} gives up on
4038 the current rule, and perhaps on all rules.
4040 Sometimes the failure of a certain command does not indicate a problem.
4041 For example, you may use the @code{mkdir} command to ensure that a
4042 directory exists. If the directory already exists, @code{mkdir} will
4043 report an error, but you probably want @code{make} to continue regardless.
4045 @cindex @code{-} (in commands)
4046 To ignore errors in a command line, write a @samp{-} at the beginning of
4047 the line's text (after the initial tab). The @samp{-} is discarded before
4048 the command is passed to the shell for execution.
4058 @cindex @code{rm} (shell command)
4061 This causes @code{rm} to continue even if it is unable to remove a file.
4064 @cindex @code{--ignore-errors}
4066 When you run @code{make} with the @samp{-i} or @samp{--ignore-errors}
4067 flag, errors are ignored in all commands of all rules. A rule in the
4068 makefile for the special target @code{.IGNORE} has the same effect, if
4069 there are no prerequisites. These ways of ignoring errors are obsolete
4070 because @samp{-} is more flexible.
4072 When errors are to be ignored, because of either a @samp{-} or the
4073 @samp{-i} flag, @code{make} treats an error return just like success,
4074 except that it prints out a message that tells you the status code
4075 the command exited with, and says that the error has been ignored.
4077 When an error happens that @code{make} has not been told to ignore,
4078 it implies that the current target cannot be correctly remade, and neither
4079 can any other that depends on it either directly or indirectly. No further
4080 commands will be executed for these targets, since their preconditions
4081 have not been achieved.
4085 @cindex @code{--keep-going}
4086 Normally @code{make} gives up immediately in this circumstance, returning a
4087 nonzero status. However, if the @samp{-k} or @samp{--keep-going}
4088 flag is specified, @code{make}
4089 continues to consider the other prerequisites of the pending targets,
4090 remaking them if necessary, before it gives up and returns nonzero status.
4091 For example, after an error in compiling one object file, @samp{make -k}
4092 will continue compiling other object files even though it already knows
4093 that linking them will be impossible. @xref{Options Summary, ,Summary of Options}.
4095 The usual behavior assumes that your purpose is to get the specified
4096 targets up to date; once @code{make} learns that this is impossible, it
4097 might as well report the failure immediately. The @samp{-k} option says
4098 that the real purpose is to test as many of the changes made in the
4099 program as possible, perhaps to find several independent problems so
4100 that you can correct them all before the next attempt to compile. This
4101 is why Emacs' @code{compile} command passes the @samp{-k} flag by
4103 @cindex Emacs (@code{M-x compile})
4105 @findex .DELETE_ON_ERROR
4106 @cindex deletion of target files
4107 @cindex removal of target files
4108 @cindex target, deleting on error
4109 Usually when a command fails, if it has changed the target file at all,
4110 the file is corrupted and cannot be used---or at least it is not
4111 completely updated. Yet the file's time stamp says that it is now up to
4112 date, so the next time @code{make} runs, it will not try to update that
4113 file. The situation is just the same as when the command is killed by a
4114 signal; @pxref{Interrupts}. So generally the right thing to do is to
4115 delete the target file if the command fails after beginning to change
4116 the file. @code{make} will do this if @code{.DELETE_ON_ERROR} appears
4117 as a target. This is almost always what you want @code{make} to do, but
4118 it is not historical practice; so for compatibility, you must explicitly
4121 @node Interrupts, Recursion, Errors, Commands
4122 @section Interrupting or Killing @code{make}
4125 @cindex deletion of target files
4126 @cindex removal of target files
4127 @cindex target, deleting on interrupt
4128 @cindex killing (interruption)
4130 If @code{make} gets a fatal signal while a command is executing, it may
4131 delete the target file that the command was supposed to update. This is
4132 done if the target file's last-modification time has changed since
4133 @code{make} first checked it.
4135 The purpose of deleting the target is to make sure that it is remade from
4136 scratch when @code{make} is next run. Why is this? Suppose you type
4137 @kbd{Ctrl-c} while a compiler is running, and it has begun to write an
4138 object file @file{foo.o}. The @kbd{Ctrl-c} kills the compiler, resulting
4139 in an incomplete file whose last-modification time is newer than the source
4140 file @file{foo.c}. But @code{make} also receives the @kbd{Ctrl-c} signal
4141 and deletes this incomplete file. If @code{make} did not do this, the next
4142 invocation of @code{make} would think that @file{foo.o} did not require
4143 updating---resulting in a strange error message from the linker when it
4144 tries to link an object file half of which is missing.
4147 You can prevent the deletion of a target file in this way by making the
4148 special target @code{.PRECIOUS} depend on it. Before remaking a target,
4149 @code{make} checks to see whether it appears on the prerequisites of
4150 @code{.PRECIOUS}, and thereby decides whether the target should be deleted
4151 if a signal happens. Some reasons why you might do this are that the
4152 target is updated in some atomic fashion, or exists only to record a
4153 modification-time (its contents do not matter), or must exist at all
4154 times to prevent other sorts of trouble.
4156 @node Recursion, Sequences, Interrupts, Commands
4157 @section Recursive Use of @code{make}
4159 @cindex subdirectories, recursion for
4161 Recursive use of @code{make} means using @code{make} as a command in a
4162 makefile. This technique is useful when you want separate makefiles for
4163 various subsystems that compose a larger system. For example, suppose you
4164 have a subdirectory @file{subdir} which has its own makefile, and you would
4165 like the containing directory's makefile to run @code{make} on the
4166 subdirectory. You can do it by writing this:
4170 cd subdir && $(MAKE)
4174 or, equivalently, this (@pxref{Options Summary, ,Summary of Options}):
4181 @cindex @code{--directory}
4183 You can write recursive @code{make} commands just by copying this example,
4184 but there are many things to know about how they work and why, and about
4185 how the sub-@code{make} relates to the top-level @code{make}. You may
4186 also find it useful to declare targets that invoke recursive
4187 @code{make} commands as @samp{.PHONY} (for more discussion on when
4188 this is useful, see @ref{Phony Targets}).
4190 @vindex @code{CURDIR}
4191 For your convenience, when GNU @code{make} starts (after it has
4192 processed any @code{-C} options) it sets the variable @code{CURDIR} to
4193 the pathname of the current working directory. This value is never
4194 touched by @code{make} again: in particular note that if you include
4195 files from other directories the value of @code{CURDIR} does not
4196 change. The value has the same precedence it would have if it were
4197 set in the makefile (by default, an environment variable @code{CURDIR}
4198 will not override this value). Note that setting this variable has no
4199 impact on the operation of @code{make} (it does not cause @code{make}
4200 to change its working directory, for example).
4203 * MAKE Variable:: The special effects of using @samp{$(MAKE)}.
4204 * Variables/Recursion:: How to communicate variables to a sub-@code{make}.
4205 * Options/Recursion:: How to communicate options to a sub-@code{make}.
4206 * -w Option:: How the @samp{-w} or @samp{--print-directory} option
4207 helps debug use of recursive @code{make} commands.
4210 @node MAKE Variable, Variables/Recursion, Recursion, Recursion
4211 @subsection How the @code{MAKE} Variable Works
4213 @cindex recursion, and @code{MAKE} variable
4215 Recursive @code{make} commands should always use the variable @code{MAKE},
4216 not the explicit command name @samp{make}, as shown here:
4221 cd subdir && $(MAKE)
4225 The value of this variable is the file name with which @code{make} was
4226 invoked. If this file name was @file{/bin/make}, then the command executed
4227 is @samp{cd subdir && /bin/make}. If you use a special version of
4228 @code{make} to run the top-level makefile, the same special version will be
4229 executed for recursive invocations.
4230 @cindex @code{cd} (shell command)
4232 @cindex +, and commands
4233 As a special feature, using the variable @code{MAKE} in the commands of
4234 a rule alters the effects of the @samp{-t} (@samp{--touch}), @samp{-n}
4235 (@samp{--just-print}), or @samp{-q} (@w{@samp{--question}}) option.
4236 Using the @code{MAKE} variable has the same effect as using a @samp{+}
4237 character at the beginning of the command line. @xref{Instead of
4238 Execution, ,Instead of Executing the Commands}. This special feature
4239 is only enabled if the @code{MAKE} variable appears directly in the
4240 command script: it does not apply if the @code{MAKE} variable is
4241 referenced through expansion of another variable. In the latter case
4242 you must use the @samp{+} token to get these special effects.@refill
4244 Consider the command @samp{make -t} in the above example. (The
4245 @samp{-t} option marks targets as up to date without actually running
4246 any commands; see @ref{Instead of Execution}.) Following the usual
4247 definition of @samp{-t}, a @samp{make -t} command in the example would
4248 create a file named @file{subsystem} and do nothing else. What you
4249 really want it to do is run @samp{@w{cd subdir &&} @w{make -t}}; but that would
4250 require executing the command, and @samp{-t} says not to execute
4252 @cindex @code{-t}, and recursion
4253 @cindex recursion, and @code{-t}
4254 @cindex @code{--touch}, and recursion
4256 The special feature makes this do what you want: whenever a command
4257 line of a rule contains the variable @code{MAKE}, the flags @samp{-t},
4258 @samp{-n} and @samp{-q} do not apply to that line. Command lines
4259 containing @code{MAKE} are executed normally despite the presence of a
4260 flag that causes most commands not to be run. The usual
4261 @code{MAKEFLAGS} mechanism passes the flags to the sub-@code{make}
4262 (@pxref{Options/Recursion, ,Communicating Options to a
4263 Sub-@code{make}}), so your request to touch the files, or print the
4264 commands, is propagated to the subsystem.@refill
4266 @node Variables/Recursion, Options/Recursion, MAKE Variable, Recursion
4267 @subsection Communicating Variables to a Sub-@code{make}
4268 @cindex sub-@code{make}
4269 @cindex environment, and recursion
4270 @cindex exporting variables
4271 @cindex variables, environment
4272 @cindex variables, exporting
4273 @cindex recursion, and environment
4274 @cindex recursion, and variables
4276 Variable values of the top-level @code{make} can be passed to the
4277 sub-@code{make} through the environment by explicit request. These
4278 variables are defined in the sub-@code{make} as defaults, but do not
4279 override what is specified in the makefile used by the sub-@code{make}
4280 makefile unless you use the @samp{-e} switch (@pxref{Options Summary,
4281 ,Summary of Options}).@refill
4283 To pass down, or @dfn{export}, a variable, @code{make} adds the variable
4284 and its value to the environment for running each command. The
4285 sub-@code{make}, in turn, uses the environment to initialize its table
4286 of variable values. @xref{Environment, ,Variables from the
4289 Except by explicit request, @code{make} exports a variable only if it
4290 is either defined in the environment initially or set on the command
4291 line, and if its name consists only of letters, numbers, and underscores.
4292 Some shells cannot cope with environment variable names consisting of
4293 characters other than letters, numbers, and underscores.
4295 @cindex SHELL, exported value
4296 The value of the @code{make} variable @code{SHELL} is not exported.
4297 Instead, the value of the @code{SHELL} variable from the invoking
4298 environment is passed to the sub-@code{make}. You can force
4299 @code{make} to export its value for @code{SHELL} by using the
4300 @code{export} directive, described below. @xref{Choosing the Shell}.
4302 The special variable @code{MAKEFLAGS} is always exported (unless you
4303 unexport it). @code{MAKEFILES} is exported if you set it to anything.
4305 @code{make} automatically passes down variable values that were defined
4306 on the command line, by putting them in the @code{MAKEFLAGS} variable.
4308 See the next section.
4311 @xref{Options/Recursion}.
4314 Variables are @emph{not} normally passed down if they were created by
4315 default by @code{make} (@pxref{Implicit Variables, ,Variables Used by
4316 Implicit Rules}). The sub-@code{make} will define these for
4320 If you want to export specific variables to a sub-@code{make}, use the
4321 @code{export} directive, like this:
4324 export @var{variable} @dots{}
4329 If you want to @emph{prevent} a variable from being exported, use the
4330 @code{unexport} directive, like this:
4333 unexport @var{variable} @dots{}
4337 In both of these forms, the arguments to @code{export} and
4338 @code{unexport} are expanded, and so could be variables or functions
4339 which expand to a (list of) variable names to be (un)exported.
4341 As a convenience, you can define a variable and export it at the same
4345 export @var{variable} = value
4349 has the same result as:
4352 @var{variable} = value
4353 export @var{variable}
4360 export @var{variable} := value
4364 has the same result as:
4367 @var{variable} := value
4368 export @var{variable}
4374 export @var{variable} += value
4381 @var{variable} += value
4382 export @var{variable}
4386 @xref{Appending, ,Appending More Text to Variables}.
4388 You may notice that the @code{export} and @code{unexport} directives
4389 work in @code{make} in the same way they work in the shell, @code{sh}.
4391 If you want all variables to be exported by default, you can use
4392 @code{export} by itself:
4399 This tells @code{make} that variables which are not explicitly mentioned
4400 in an @code{export} or @code{unexport} directive should be exported.
4401 Any variable given in an @code{unexport} directive will still @emph{not}
4402 be exported. If you use @code{export} by itself to export variables by
4403 default, variables whose names contain characters other than
4404 alphanumerics and underscores will not be exported unless specifically
4405 mentioned in an @code{export} directive.@refill
4407 @findex .EXPORT_ALL_VARIABLES
4408 The behavior elicited by an @code{export} directive by itself was the
4409 default in older versions of GNU @code{make}. If your makefiles depend
4410 on this behavior and you want to be compatible with old versions of
4411 @code{make}, you can write a rule for the special target
4412 @code{.EXPORT_ALL_VARIABLES} instead of using the @code{export} directive.
4413 This will be ignored by old @code{make}s, while the @code{export}
4414 directive will cause a syntax error.@refill
4415 @cindex compatibility in exporting
4417 Likewise, you can use @code{unexport} by itself to tell @code{make}
4418 @emph{not} to export variables by default. Since this is the default
4419 behavior, you would only need to do this if @code{export} had been used
4420 by itself earlier (in an included makefile, perhaps). You
4421 @strong{cannot} use @code{export} and @code{unexport} by themselves to
4422 have variables exported for some commands and not for others. The last
4423 @code{export} or @code{unexport} directive that appears by itself
4424 determines the behavior for the entire run of @code{make}.@refill
4427 @cindex recursion, level of
4428 As a special feature, the variable @code{MAKELEVEL} is changed when it
4429 is passed down from level to level. This variable's value is a string
4430 which is the depth of the level as a decimal number. The value is
4431 @samp{0} for the top-level @code{make}; @samp{1} for a sub-@code{make},
4432 @samp{2} for a sub-sub-@code{make}, and so on. The incrementation
4433 happens when @code{make} sets up the environment for a command.@refill
4435 The main use of @code{MAKELEVEL} is to test it in a conditional
4436 directive (@pxref{Conditionals, ,Conditional Parts of Makefiles}); this
4437 way you can write a makefile that behaves one way if run recursively and
4438 another way if run directly by you.@refill
4441 You can use the variable @code{MAKEFILES} to cause all sub-@code{make}
4442 commands to use additional makefiles. The value of @code{MAKEFILES} is
4443 a whitespace-separated list of file names. This variable, if defined in
4444 the outer-level makefile, is passed down through the environment; then
4445 it serves as a list of extra makefiles for the sub-@code{make} to read
4446 before the usual or specified ones. @xref{MAKEFILES Variable, ,The
4447 Variable @code{MAKEFILES}}.@refill
4449 @node Options/Recursion, -w Option, Variables/Recursion, Recursion
4450 @subsection Communicating Options to a Sub-@code{make}
4451 @cindex options, and recursion
4452 @cindex recursion, and options
4455 Flags such as @samp{-s} and @samp{-k} are passed automatically to the
4456 sub-@code{make} through the variable @code{MAKEFLAGS}. This variable is
4457 set up automatically by @code{make} to contain the flag letters that
4458 @code{make} received. Thus, if you do @w{@samp{make -ks}} then
4459 @code{MAKEFLAGS} gets the value @samp{ks}.@refill
4461 As a consequence, every sub-@code{make} gets a value for @code{MAKEFLAGS}
4462 in its environment. In response, it takes the flags from that value and
4463 processes them as if they had been given as arguments.
4464 @xref{Options Summary, ,Summary of Options}.
4466 @cindex command line variable definitions, and recursion
4467 @cindex variables, command line, and recursion
4468 @cindex recursion, and command line variable definitions
4469 Likewise variables defined on the command line are passed to the
4470 sub-@code{make} through @code{MAKEFLAGS}. Words in the value of
4471 @code{MAKEFLAGS} that contain @samp{=}, @code{make} treats as variable
4472 definitions just as if they appeared on the command line.
4473 @xref{Overriding, ,Overriding Variables}.
4475 @cindex @code{-C}, and recursion
4476 @cindex @code{-f}, and recursion
4477 @cindex @code{-o}, and recursion
4478 @cindex @code{-W}, and recursion
4479 @cindex @code{--directory}, and recursion
4480 @cindex @code{--file}, and recursion
4481 @cindex @code{--old-file}, and recursion
4482 @cindex @code{--assume-old}, and recursion
4483 @cindex @code{--assume-new}, and recursion
4484 @cindex @code{--new-file}, and recursion
4485 @cindex recursion, and @code{-C}
4486 @cindex recursion, and @code{-f}
4487 @cindex recursion, and @code{-o}
4488 @cindex recursion, and @code{-W}
4489 The options @samp{-C}, @samp{-f}, @samp{-o}, and @samp{-W} are not put
4490 into @code{MAKEFLAGS}; these options are not passed down.@refill
4492 @cindex @code{-j}, and recursion
4493 @cindex @code{--jobs}, and recursion
4494 @cindex recursion, and @code{-j}
4495 @cindex job slots, and recursion
4496 The @samp{-j} option is a special case (@pxref{Parallel, ,Parallel Execution}).
4497 If you set it to some numeric value @samp{N} and your operating system
4498 supports it (most any UNIX system will; others typically won't), the
4499 parent @code{make} and all the sub-@code{make}s will communicate to
4500 ensure that there are only @samp{N} jobs running at the same time
4501 between them all. Note that any job that is marked recursive
4502 (@pxref{Instead of Execution, ,Instead of Executing the Commands})
4503 doesn't count against the total jobs (otherwise we could get @samp{N}
4504 sub-@code{make}s running and have no slots left over for any real work!)
4506 If your operating system doesn't support the above communication, then
4507 @samp{-j 1} is always put into @code{MAKEFLAGS} instead of the value you
4508 specified. This is because if the @w{@samp{-j}} option were passed down
4509 to sub-@code{make}s, you would get many more jobs running in parallel
4510 than you asked for. If you give @samp{-j} with no numeric argument,
4511 meaning to run as many jobs as possible in parallel, this is passed
4512 down, since multiple infinities are no more than one.@refill
4514 If you do not want to pass the other flags down, you must change the
4515 value of @code{MAKEFLAGS}, like this:
4519 cd subdir && $(MAKE) MAKEFLAGS=
4522 @vindex MAKEOVERRIDES
4523 The command line variable definitions really appear in the variable
4524 @code{MAKEOVERRIDES}, and @code{MAKEFLAGS} contains a reference to this
4525 variable. If you do want to pass flags down normally, but don't want to
4526 pass down the command line variable definitions, you can reset
4527 @code{MAKEOVERRIDES} to empty, like this:
4534 @cindex Arg list too long
4536 This is not usually useful to do. However, some systems have a small
4537 fixed limit on the size of the environment, and putting so much
4538 information into the value of @code{MAKEFLAGS} can exceed it. If you
4539 see the error message @samp{Arg list too long}, this may be the problem.
4542 (For strict compliance with POSIX.2, changing @code{MAKEOVERRIDES} does
4543 not affect @code{MAKEFLAGS} if the special target @samp{.POSIX} appears
4544 in the makefile. You probably do not care about this.)
4547 A similar variable @code{MFLAGS} exists also, for historical
4548 compatibility. It has the same value as @code{MAKEFLAGS} except that it
4549 does not contain the command line variable definitions, and it always
4550 begins with a hyphen unless it is empty (@code{MAKEFLAGS} begins with a
4551 hyphen only when it begins with an option that has no single-letter
4552 version, such as @samp{--warn-undefined-variables}). @code{MFLAGS} was
4553 traditionally used explicitly in the recursive @code{make} command, like
4558 cd subdir && $(MAKE) $(MFLAGS)
4562 but now @code{MAKEFLAGS} makes this usage redundant. If you want your
4563 makefiles to be compatible with old @code{make} programs, use this
4564 technique; it will work fine with more modern @code{make} versions too.
4566 @cindex setting options from environment
4567 @cindex options, setting from environment
4568 @cindex setting options in makefiles
4569 @cindex options, setting in makefiles
4570 The @code{MAKEFLAGS} variable can also be useful if you want to have
4571 certain options, such as @samp{-k} (@pxref{Options Summary, ,Summary of
4572 Options}), set each time you run @code{make}. You simply put a value for
4573 @code{MAKEFLAGS} in your environment. You can also set @code{MAKEFLAGS} in
4574 a makefile, to specify additional flags that should also be in effect for
4575 that makefile. (Note that you cannot use @code{MFLAGS} this way. That
4576 variable is set only for compatibility; @code{make} does not interpret a
4577 value you set for it in any way.)
4579 When @code{make} interprets the value of @code{MAKEFLAGS} (either from the
4580 environment or from a makefile), it first prepends a hyphen if the value
4581 does not already begin with one. Then it chops the value into words
4582 separated by blanks, and parses these words as if they were options given
4583 on the command line (except that @samp{-C}, @samp{-f}, @samp{-h},
4584 @samp{-o}, @samp{-W}, and their long-named versions are ignored; and there
4585 is no error for an invalid option).
4587 If you do put @code{MAKEFLAGS} in your environment, you should be sure not
4588 to include any options that will drastically affect the actions of
4589 @code{make} and undermine the purpose of makefiles and of @code{make}
4590 itself. For instance, the @samp{-t}, @samp{-n}, and @samp{-q} options, if
4591 put in one of these variables, could have disastrous consequences and would
4592 certainly have at least surprising and probably annoying effects.@refill
4594 @node -w Option, , Options/Recursion, Recursion
4595 @subsection The @samp{--print-directory} Option
4596 @cindex directories, printing them
4597 @cindex printing directories
4598 @cindex recursion, and printing directories
4600 If you use several levels of recursive @code{make} invocations, the
4601 @samp{-w} or @w{@samp{--print-directory}} option can make the output a
4602 lot easier to understand by showing each directory as @code{make}
4603 starts processing it and as @code{make} finishes processing it. For
4604 example, if @samp{make -w} is run in the directory @file{/u/gnu/make},
4605 @code{make} will print a line of the form:@refill
4608 make: Entering directory `/u/gnu/make'.
4612 before doing anything else, and a line of the form:
4615 make: Leaving directory `/u/gnu/make'.
4619 when processing is completed.
4621 @cindex @code{-C}, and @code{-w}
4622 @cindex @code{--directory}, and @code{--print-directory}
4623 @cindex recursion, and @code{-w}
4624 @cindex @code{-w}, and @code{-C}
4625 @cindex @code{-w}, and recursion
4626 @cindex @code{--print-directory}, and @code{--directory}
4627 @cindex @code{--print-directory}, and recursion
4628 @cindex @code{--no-print-directory}
4629 @cindex @code{--print-directory}, disabling
4630 @cindex @code{-w}, disabling
4631 Normally, you do not need to specify this option because @samp{make}
4632 does it for you: @samp{-w} is turned on automatically when you use the
4633 @samp{-C} option, and in sub-@code{make}s. @code{make} will not
4634 automatically turn on @samp{-w} if you also use @samp{-s}, which says to
4635 be silent, or if you use @samp{--no-print-directory} to explicitly
4638 @node Sequences, Empty Commands, Recursion, Commands
4639 @section Defining Canned Command Sequences
4640 @cindex sequences of commands
4641 @cindex commands, sequences of
4643 When the same sequence of commands is useful in making various targets, you
4644 can define it as a canned sequence with the @code{define} directive, and
4645 refer to the canned sequence from the rules for those targets. The canned
4646 sequence is actually a variable, so the name must not conflict with other
4649 Here is an example of defining a canned sequence of commands:
4653 yacc $(firstword $^)
4660 Here @code{run-yacc} is the name of the variable being defined;
4661 @code{endef} marks the end of the definition; the lines in between are the
4662 commands. The @code{define} directive does not expand variable references
4663 and function calls in the canned sequence; the @samp{$} characters,
4664 parentheses, variable names, and so on, all become part of the value of the
4665 variable you are defining.
4666 @xref{Defining, ,Defining Variables Verbatim},
4667 for a complete explanation of @code{define}.
4669 The first command in this example runs Yacc on the first prerequisite of
4670 whichever rule uses the canned sequence. The output file from Yacc is
4671 always named @file{y.tab.c}. The second command moves the output to the
4672 rule's target file name.
4674 To use the canned sequence, substitute the variable into the commands of a
4675 rule. You can substitute it like any other variable
4676 (@pxref{Reference, ,Basics of Variable References}).
4677 Because variables defined by @code{define} are recursively expanded
4678 variables, all the variable references you wrote inside the @code{define}
4679 are expanded now. For example:
4687 @samp{foo.y} will be substituted for the variable @samp{$^} when it occurs in
4688 @code{run-yacc}'s value, and @samp{foo.c} for @samp{$@@}.@refill
4690 This is a realistic example, but this particular one is not needed in
4691 practice because @code{make} has an implicit rule to figure out these
4692 commands based on the file names involved
4693 (@pxref{Implicit Rules, ,Using Implicit Rules}).
4695 @cindex @@, and @code{define}
4696 @cindex -, and @code{define}
4697 @cindex +, and @code{define}
4698 In command execution, each line of a canned sequence is treated just as
4699 if the line appeared on its own in the rule, preceded by a tab. In
4700 particular, @code{make} invokes a separate subshell for each line. You
4701 can use the special prefix characters that affect command lines
4702 (@samp{@@}, @samp{-}, and @samp{+}) on each line of a canned sequence.
4703 @xref{Commands, ,Writing the Commands in Rules}.
4704 For example, using this canned sequence:
4708 @@echo "frobnicating target $@@"
4709 frob-step-1 $< -o $@@-step-1
4710 frob-step-2 $@@-step-1 -o $@@
4715 @code{make} will not echo the first line, the @code{echo} command.
4716 But it @emph{will} echo the following two command lines.
4718 On the other hand, prefix characters on the command line that refers to
4719 a canned sequence apply to every line in the sequence. So the rule:
4727 does not echo @emph{any} commands.
4728 (@xref{Echoing, ,Command Echoing}, for a full explanation of @samp{@@}.)
4730 @node Empty Commands, , Sequences, Commands
4731 @section Using Empty Commands
4732 @cindex empty commands
4733 @cindex commands, empty
4735 It is sometimes useful to define commands which do nothing. This is done
4736 simply by giving a command that consists of nothing but whitespace. For
4744 defines an empty command string for @file{target}. You could also use a
4745 line beginning with a tab character to define an empty command string,
4746 but this would be confusing because such a line looks empty.
4748 @findex .DEFAULT@r{, and empty commands}
4749 You may be wondering why you would want to define a command string that
4750 does nothing. The only reason this is useful is to prevent a target
4751 from getting implicit commands (from implicit rules or the
4752 @code{.DEFAULT} special target; @pxref{Implicit Rules} and
4753 @pxref{Last Resort, ,Defining Last-Resort Default Rules}).@refill
4755 @c !!! another reason is for canonical stamp files:
4760 create foo frm foo.in
4765 You may be inclined to define empty command strings for targets that are
4766 not actual files, but only exist so that their prerequisites can be
4767 remade. However, this is not the best way to do that, because the
4768 prerequisites may not be remade properly if the target file actually does exist.
4769 @xref{Phony Targets, ,Phony Targets}, for a better way to do this.
4771 @node Using Variables, Conditionals, Commands, Top
4772 @chapter How to Use Variables
4775 @cindex recursive variable expansion
4776 @cindex simple variable expansion
4778 A @dfn{variable} is a name defined in a makefile to represent a string
4779 of text, called the variable's @dfn{value}. These values are
4780 substituted by explicit request into targets, prerequisites, commands,
4781 and other parts of the makefile. (In some other versions of @code{make},
4782 variables are called @dfn{macros}.)
4785 Variables and functions in all parts of a makefile are expanded when
4786 read, except for the shell commands in rules, the right-hand sides of
4787 variable definitions using @samp{=}, and the bodies of variable
4788 definitions using the @code{define} directive.@refill
4790 Variables can represent lists of file names, options to pass to compilers,
4791 programs to run, directories to look in for source files, directories to
4792 write output in, or anything else you can imagine.
4794 A variable name may be any sequence of characters not containing @samp{:},
4795 @samp{#}, @samp{=}, or leading or trailing whitespace. However,
4796 variable names containing characters other than letters, numbers, and
4797 underscores should be avoided, as they may be given special meanings in the
4798 future, and with some shells they cannot be passed through the environment to a
4800 (@pxref{Variables/Recursion, ,Communicating Variables to a Sub-@code{make}}).
4802 Variable names are case-sensitive. The names @samp{foo}, @samp{FOO},
4803 and @samp{Foo} all refer to different variables.
4805 It is traditional to use upper case letters in variable names, but we
4806 recommend using lower case letters for variable names that serve internal
4807 purposes in the makefile, and reserving upper case for parameters that
4808 control implicit rules or for parameters that the user should override with
4809 command options (@pxref{Overriding, ,Overriding Variables}).
4811 A few variables have names that are a single punctuation character or
4812 just a few characters. These are the @dfn{automatic variables}, and
4813 they have particular specialized uses. @xref{Automatic Variables}.
4816 * Reference:: How to use the value of a variable.
4817 * Flavors:: Variables come in two flavors.
4818 * Advanced:: Advanced features for referencing a variable.
4819 * Values:: All the ways variables get their values.
4820 * Setting:: How to set a variable in the makefile.
4821 * Appending:: How to append more text to the old value
4823 * Override Directive:: How to set a variable in the makefile even if
4824 the user has set it with a command argument.
4825 * Defining:: An alternate way to set a variable
4826 to a verbatim string.
4827 * Environment:: Variable values can come from the environment.
4828 * Target-specific:: Variable values can be defined on a per-target
4830 * Pattern-specific:: Target-specific variable values can be applied
4831 to a group of targets that match a pattern.
4834 @node Reference, Flavors, Using Variables, Using Variables
4835 @section Basics of Variable References
4836 @cindex variables, how to reference
4837 @cindex reference to variables
4838 @cindex @code{$}, in variable reference
4839 @cindex dollar sign (@code{$}), in variable reference
4841 To substitute a variable's value, write a dollar sign followed by the name
4842 of the variable in parentheses or braces: either @samp{$(foo)} or
4843 @samp{$@{foo@}} is a valid reference to the variable @code{foo}. This
4844 special significance of @samp{$} is why you must write @samp{$$} to have
4845 the effect of a single dollar sign in a file name or command.
4847 Variable references can be used in any context: targets, prerequisites,
4848 commands, most directives, and new variable values. Here is an
4849 example of a common case, where a variable holds the names of all the
4850 object files in a program:
4854 objects = program.o foo.o utils.o
4855 program : $(objects)
4856 cc -o program $(objects)
4862 Variable references work by strict textual substitution. Thus, the rule
4867 prog.o : prog.$(foo)
4868 $(foo)$(foo) -$(foo) prog.$(foo)
4873 could be used to compile a C program @file{prog.c}. Since spaces before
4874 the variable value are ignored in variable assignments, the value of
4875 @code{foo} is precisely @samp{c}. (Don't actually write your makefiles
4878 A dollar sign followed by a character other than a dollar sign,
4879 open-parenthesis or open-brace treats that single character as the
4880 variable name. Thus, you could reference the variable @code{x} with
4881 @samp{$x}. However, this practice is strongly discouraged, except in
4882 the case of the automatic variables (@pxref{Automatic Variables}).
4884 @node Flavors, Advanced, Reference, Using Variables
4885 @section The Two Flavors of Variables
4886 @cindex flavors of variables
4887 @cindex recursive variable expansion
4888 @cindex variables, flavors
4889 @cindex recursively expanded variables
4890 @cindex variables, recursively expanded
4892 There are two ways that a variable in GNU @code{make} can have a value;
4893 we call them the two @dfn{flavors} of variables. The two flavors are
4894 distinguished in how they are defined and in what they do when expanded.
4897 The first flavor of variable is a @dfn{recursively expanded} variable.
4898 Variables of this sort are defined by lines using @samp{=}
4899 (@pxref{Setting, ,Setting Variables}) or by the @code{define} directive
4900 (@pxref{Defining, ,Defining Variables Verbatim}). The value you specify
4901 is installed verbatim; if it contains references to other variables,
4902 these references are expanded whenever this variable is substituted (in
4903 the course of expanding some other string). When this happens, it is
4904 called @dfn{recursive expansion}.@refill
4917 will echo @samp{Huh?}: @samp{$(foo)} expands to @samp{$(bar)} which
4918 expands to @samp{$(ugh)} which finally expands to @samp{Huh?}.@refill
4920 This flavor of variable is the only sort supported by other versions of
4921 @code{make}. It has its advantages and its disadvantages. An advantage
4922 (most would say) is that:
4925 CFLAGS = $(include_dirs) -O
4926 include_dirs = -Ifoo -Ibar
4930 will do what was intended: when @samp{CFLAGS} is expanded in a command,
4931 it will expand to @samp{-Ifoo -Ibar -O}. A major disadvantage is that you
4932 cannot append something on the end of a variable, as in
4935 CFLAGS = $(CFLAGS) -O
4939 because it will cause an infinite loop in the variable expansion.
4940 (Actually @code{make} detects the infinite loop and reports an error.)
4941 @cindex loops in variable expansion
4942 @cindex variables, loops in expansion
4944 Another disadvantage is that any functions
4945 (@pxref{Functions, ,Functions for Transforming Text})
4946 referenced in the definition will be executed every time the variable is
4947 expanded. This makes @code{make} run slower; worse, it causes the
4948 @code{wildcard} and @code{shell} functions to give unpredictable results
4949 because you cannot easily control when they are called, or even how many
4952 To avoid all the problems and inconveniences of recursively expanded
4953 variables, there is another flavor: simply expanded variables.
4955 @cindex simply expanded variables
4956 @cindex variables, simply expanded
4958 @dfn{Simply expanded variables} are defined by lines using @samp{:=}
4959 (@pxref{Setting, ,Setting Variables}).
4960 The value of a simply expanded variable is scanned
4961 once and for all, expanding any references to other variables and
4962 functions, when the variable is defined. The actual value of the simply
4963 expanded variable is the result of expanding the text that you write.
4964 It does not contain any references to other variables; it contains their
4965 values @emph{as of the time this variable was defined}. Therefore,
4981 When a simply expanded variable is referenced, its value is substituted
4984 Here is a somewhat more complicated example, illustrating the use of
4985 @samp{:=} in conjunction with the @code{shell} function.
4986 (@xref{Shell Function, , The @code{shell} Function}.) This example
4987 also shows use of the variable @code{MAKELEVEL}, which is changed
4988 when it is passed down from level to level.
4989 (@xref{Variables/Recursion, , Communicating Variables to a
4990 Sub-@code{make}}, for information about @code{MAKELEVEL}.)
4996 ifeq (0,$@{MAKELEVEL@})
4997 whoami := $(shell whoami)
4998 host-type := $(shell arch)
4999 MAKE := $@{MAKE@} host-type=$@{host-type@} whoami=$@{whoami@}
5005 An advantage of this use of @samp{:=} is that a typical
5006 `descend into a directory' command then looks like this:
5011 $@{MAKE@} -C $@@ all
5015 Simply expanded variables generally make complicated makefile programming
5016 more predictable because they work like variables in most programming
5017 languages. They allow you to redefine a variable using its own value (or
5018 its value processed in some way by one of the expansion functions) and to
5019 use the expansion functions much more efficiently
5020 (@pxref{Functions, ,Functions for Transforming Text}).
5022 @cindex spaces, in variable values
5023 @cindex whitespace, in variable values
5024 @cindex variables, spaces in values
5025 You can also use them to introduce controlled leading whitespace into
5026 variable values. Leading whitespace characters are discarded from your
5027 input before substitution of variable references and function calls;
5028 this means you can include leading spaces in a variable value by
5029 protecting them with variable references, like this:
5033 space := $(nullstring) # end of the line
5037 Here the value of the variable @code{space} is precisely one space. The
5038 comment @w{@samp{# end of the line}} is included here just for clarity.
5039 Since trailing space characters are @emph{not} stripped from variable
5040 values, just a space at the end of the line would have the same effect
5041 (but be rather hard to read). If you put whitespace at the end of a
5042 variable value, it is a good idea to put a comment like that at the end
5043 of the line to make your intent clear. Conversely, if you do @emph{not}
5044 want any whitespace characters at the end of your variable value, you
5045 must remember not to put a random comment on the end of the line after
5046 some whitespace, such as this:
5049 dir := /foo/bar # directory to put the frobs in
5053 Here the value of the variable @code{dir} is @w{@samp{/foo/bar }}
5054 (with four trailing spaces), which was probably not the intention.
5055 (Imagine something like @w{@samp{$(dir)/file}} with this definition!)
5057 @cindex conditional variable assignment
5058 @cindex variables, conditional assignment
5060 There is another assignment operator for variables, @samp{?=}. This
5061 is called a conditional variable assignment operator, because it only
5062 has an effect if the variable is not yet defined. This statement:
5069 is exactly equivalent to this
5070 (@pxref{Origin Function, ,The @code{origin} Function}):
5073 ifeq ($(origin FOO), undefined)
5078 Note that a variable set to an empty value is still defined, so
5079 @samp{?=} will not set that variable.
5081 @node Advanced, Values, Flavors, Using Variables
5082 @section Advanced Features for Reference to Variables
5083 @cindex reference to variables
5085 This section describes some advanced features you can use to reference
5086 variables in more flexible ways.
5089 * Substitution Refs:: Referencing a variable with
5090 substitutions on the value.
5091 * Computed Names:: Computing the name of the variable to refer to.
5094 @node Substitution Refs, Computed Names, Advanced, Advanced
5095 @subsection Substitution References
5096 @cindex modified variable reference
5097 @cindex substitution variable reference
5098 @cindex variables, modified reference
5099 @cindex variables, substitution reference
5101 @cindex variables, substituting suffix in
5102 @cindex suffix, substituting in variables
5103 A @dfn{substitution reference} substitutes the value of a variable with
5104 alterations that you specify. It has the form
5105 @samp{$(@var{var}:@var{a}=@var{b})} (or
5106 @samp{$@{@var{var}:@var{a}=@var{b}@}}) and its meaning is to take the value
5107 of the variable @var{var}, replace every @var{a} at the end of a word with
5108 @var{b} in that value, and substitute the resulting string.
5110 When we say ``at the end of a word'', we mean that @var{a} must appear
5111 either followed by whitespace or at the end of the value in order to be
5112 replaced; other occurrences of @var{a} in the value are unaltered. For
5121 sets @samp{bar} to @samp{a.c b.c c.c}. @xref{Setting, ,Setting Variables}.
5123 A substitution reference is actually an abbreviation for use of the
5124 @code{patsubst} expansion function (@pxref{Text Functions, ,Functions for String Substitution and Analysis}). We provide
5125 substitution references as well as @code{patsubst} for compatibility with
5126 other implementations of @code{make}.
5129 Another type of substitution reference lets you use the full power of
5130 the @code{patsubst} function. It has the same form
5131 @samp{$(@var{var}:@var{a}=@var{b})} described above, except that now
5132 @var{a} must contain a single @samp{%} character. This case is
5133 equivalent to @samp{$(patsubst @var{a},@var{b},$(@var{var}))}.
5134 @xref{Text Functions, ,Functions for String Substitution and Analysis},
5135 for a description of the @code{patsubst} function.@refill
5139 @exdent For example:
5142 bar := $(foo:%.o=%.c)
5147 sets @samp{bar} to @samp{a.c b.c c.c}.
5149 @node Computed Names, , Substitution Refs, Advanced
5150 @subsection Computed Variable Names
5151 @cindex nested variable reference
5152 @cindex computed variable name
5153 @cindex variables, computed names
5154 @cindex variables, nested references
5155 @cindex variables, @samp{$} in name
5156 @cindex @code{$}, in variable name
5157 @cindex dollar sign (@code{$}), in variable name
5159 Computed variable names are a complicated concept needed only for
5160 sophisticated makefile programming. For most purposes you need not
5161 consider them, except to know that making a variable with a dollar sign
5162 in its name might have strange results. However, if you are the type
5163 that wants to understand everything, or you are actually interested in
5164 what they do, read on.
5166 Variables may be referenced inside the name of a variable. This is
5167 called a @dfn{computed variable name} or a @dfn{nested variable
5168 reference}. For example,
5177 defines @code{a} as @samp{z}: the @samp{$(x)} inside @samp{$($(x))} expands
5178 to @samp{y}, so @samp{$($(x))} expands to @samp{$(y)} which in turn expands
5179 to @samp{z}. Here the name of the variable to reference is not stated
5180 explicitly; it is computed by expansion of @samp{$(x)}. The reference
5181 @samp{$(x)} here is nested within the outer variable reference.
5183 The previous example shows two levels of nesting, but any number of levels
5184 is possible. For example, here are three levels:
5194 Here the innermost @samp{$(x)} expands to @samp{y}, so @samp{$($(x))}
5195 expands to @samp{$(y)} which in turn expands to @samp{z}; now we have
5196 @samp{$(z)}, which becomes @samp{u}.
5198 References to recursively-expanded variables within a variable name are
5199 reexpanded in the usual fashion. For example:
5209 defines @code{a} as @samp{Hello}: @samp{$($(x))} becomes @samp{$($(y))}
5210 which becomes @samp{$(z)} which becomes @samp{Hello}.
5212 Nested variable references can also contain modified references and
5213 function invocations (@pxref{Functions, ,Functions for Transforming Text}),
5214 just like any other reference.
5215 For example, using the @code{subst} function
5216 (@pxref{Text Functions, ,Functions for String Substitution and Analysis}):
5222 y = $(subst 1,2,$(x))
5229 eventually defines @code{a} as @samp{Hello}. It is doubtful that anyone
5230 would ever want to write a nested reference as convoluted as this one, but
5231 it works: @samp{$($($(z)))} expands to @samp{$($(y))} which becomes
5232 @samp{$($(subst 1,2,$(x)))}. This gets the value @samp{variable1} from
5233 @code{x} and changes it by substitution to @samp{variable2}, so that the
5234 entire string becomes @samp{$(variable2)}, a simple variable reference
5235 whose value is @samp{Hello}.@refill
5237 A computed variable name need not consist entirely of a single variable
5238 reference. It can contain several variable references, as well as some
5239 invariant text. For example,
5248 a_files := filea fileb
5249 1_files := file1 file2
5253 ifeq "$(use_a)" "yes"
5261 ifeq "$(use_dirs)" "yes"
5267 dirs := $($(a1)_$(df))
5272 will give @code{dirs} the same value as @code{a_dirs}, @code{1_dirs},
5273 @code{a_files} or @code{1_files} depending on the settings of @code{use_a}
5274 and @code{use_dirs}.@refill
5276 Computed variable names can also be used in substitution references:
5280 a_objects := a.o b.o c.o
5281 1_objects := 1.o 2.o 3.o
5283 sources := $($(a1)_objects:.o=.c)
5288 defines @code{sources} as either @samp{a.c b.c c.c} or @samp{1.c 2.c 3.c},
5289 depending on the value of @code{a1}.
5291 The only restriction on this sort of use of nested variable references
5292 is that they cannot specify part of the name of a function to be called.
5293 This is because the test for a recognized function name is done before
5294 the expansion of nested references. For example,
5310 foo := $($(func) $(bar))
5315 attempts to give @samp{foo} the value of the variable @samp{sort a d b g
5316 q c} or @samp{strip a d b g q c}, rather than giving @samp{a d b g q c}
5317 as the argument to either the @code{sort} or the @code{strip} function.
5318 This restriction could be removed in the future if that change is shown
5321 You can also use computed variable names in the left-hand side of a
5322 variable assignment, or in a @code{define} directive, as in:
5326 $(dir)_sources := $(wildcard $(dir)/*.c)
5328 lpr $($(dir)_sources)
5333 This example defines the variables @samp{dir}, @samp{foo_sources}, and
5336 Note that @dfn{nested variable references} are quite different from
5337 @dfn{recursively expanded variables}
5338 (@pxref{Flavors, ,The Two Flavors of Variables}), though both are
5339 used together in complex ways when doing makefile programming.@refill
5341 @node Values, Setting, Advanced, Using Variables
5342 @section How Variables Get Their Values
5343 @cindex variables, how they get their values
5344 @cindex value, how a variable gets it
5346 Variables can get values in several different ways:
5350 You can specify an overriding value when you run @code{make}.
5351 @xref{Overriding, ,Overriding Variables}.
5354 You can specify a value in the makefile, either
5355 with an assignment (@pxref{Setting, ,Setting Variables}) or with a
5356 verbatim definition (@pxref{Defining, ,Defining Variables Verbatim}).@refill
5359 Variables in the environment become @code{make} variables.
5360 @xref{Environment, ,Variables from the Environment}.
5363 Several @dfn{automatic} variables are given new values for each rule.
5364 Each of these has a single conventional use.
5365 @xref{Automatic Variables}.
5368 Several variables have constant initial values.
5369 @xref{Implicit Variables, ,Variables Used by Implicit Rules}.
5372 @node Setting, Appending, Values, Using Variables
5373 @section Setting Variables
5374 @cindex setting variables
5375 @cindex variables, setting
5380 To set a variable from the makefile, write a line starting with the
5381 variable name followed by @samp{=} or @samp{:=}. Whatever follows the
5382 @samp{=} or @samp{:=} on the line becomes the value. For example,
5385 objects = main.o foo.o bar.o utils.o
5389 defines a variable named @code{objects}. Whitespace around the variable
5390 name and immediately after the @samp{=} is ignored.
5392 Variables defined with @samp{=} are @dfn{recursively expanded} variables.
5393 Variables defined with @samp{:=} are @dfn{simply expanded} variables; these
5394 definitions can contain variable references which will be expanded before
5395 the definition is made. @xref{Flavors, ,The Two Flavors of Variables}.
5397 The variable name may contain function and variable references, which
5398 are expanded when the line is read to find the actual variable name to use.
5400 There is no limit on the length of the value of a variable except the
5401 amount of swapping space on the computer. When a variable definition is
5402 long, it is a good idea to break it into several lines by inserting
5403 backslash-newline at convenient places in the definition. This will not
5404 affect the functioning of @code{make}, but it will make the makefile easier
5407 Most variable names are considered to have the empty string as a value if
5408 you have never set them. Several variables have built-in initial values
5409 that are not empty, but you can set them in the usual ways
5410 (@pxref{Implicit Variables, ,Variables Used by Implicit Rules}).
5411 Several special variables are set
5412 automatically to a new value for each rule; these are called the
5413 @dfn{automatic} variables (@pxref{Automatic Variables}).
5415 If you'd like a variable to be set to a value only if it's not already
5416 set, then you can use the shorthand operator @samp{?=} instead of
5417 @samp{=}. These two settings of the variable @samp{FOO} are identical
5418 (@pxref{Origin Function, ,The @code{origin} Function}):
5428 ifeq ($(origin FOO), undefined)
5433 @node Appending, Override Directive, Setting, Using Variables
5434 @section Appending More Text to Variables
5436 @cindex appending to variables
5437 @cindex variables, appending to
5439 Often it is useful to add more text to the value of a variable already defined.
5440 You do this with a line containing @samp{+=}, like this:
5443 objects += another.o
5447 This takes the value of the variable @code{objects}, and adds the text
5448 @samp{another.o} to it (preceded by a single space). Thus:
5451 objects = main.o foo.o bar.o utils.o
5452 objects += another.o
5456 sets @code{objects} to @samp{main.o foo.o bar.o utils.o another.o}.
5458 Using @samp{+=} is similar to:
5461 objects = main.o foo.o bar.o utils.o
5462 objects := $(objects) another.o
5466 but differs in ways that become important when you use more complex values.
5468 When the variable in question has not been defined before, @samp{+=}
5469 acts just like normal @samp{=}: it defines a recursively-expanded
5470 variable. However, when there @emph{is} a previous definition, exactly
5471 what @samp{+=} does depends on what flavor of variable you defined
5472 originally. @xref{Flavors, ,The Two Flavors of Variables}, for an
5473 explanation of the two flavors of variables.
5475 When you add to a variable's value with @samp{+=}, @code{make} acts
5476 essentially as if you had included the extra text in the initial
5477 definition of the variable. If you defined it first with @samp{:=},
5478 making it a simply-expanded variable, @samp{+=} adds to that
5479 simply-expanded definition, and expands the new text before appending it
5480 to the old value just as @samp{:=} does
5481 (see @ref{Setting, ,Setting Variables}, for a full explanation of @samp{:=}).
5490 is exactly equivalent to:
5495 variable := $(variable) more
5498 On the other hand, when you use @samp{+=} with a variable that you defined
5499 first to be recursively-expanded using plain @samp{=}, @code{make} does
5500 something a bit different. Recall that when you define a
5501 recursively-expanded variable, @code{make} does not expand the value you set
5502 for variable and function references immediately. Instead it stores the text
5503 verbatim, and saves these variable and function references to be expanded
5504 later, when you refer to the new variable (@pxref{Flavors, ,The Two Flavors
5505 of Variables}). When you use @samp{+=} on a recursively-expanded variable,
5506 it is this unexpanded text to which @code{make} appends the new text you
5517 is roughly equivalent to:
5522 variable = $(temp) more
5527 except that of course it never defines a variable called @code{temp}.
5528 The importance of this comes when the variable's old value contains
5529 variable references. Take this common example:
5532 CFLAGS = $(includes) -O
5534 CFLAGS += -pg # enable profiling
5538 The first line defines the @code{CFLAGS} variable with a reference to another
5539 variable, @code{includes}. (@code{CFLAGS} is used by the rules for C
5540 compilation; @pxref{Catalogue of Rules, ,Catalogue of Implicit Rules}.)
5541 Using @samp{=} for the definition makes @code{CFLAGS} a recursively-expanded
5542 variable, meaning @w{@samp{$(includes) -O}} is @emph{not} expanded when
5543 @code{make} processes the definition of @code{CFLAGS}. Thus, @code{includes}
5544 need not be defined yet for its value to take effect. It only has to be
5545 defined before any reference to @code{CFLAGS}. If we tried to append to the
5546 value of @code{CFLAGS} without using @samp{+=}, we might do it like this:
5549 CFLAGS := $(CFLAGS) -pg # enable profiling
5553 This is pretty close, but not quite what we want. Using @samp{:=}
5554 redefines @code{CFLAGS} as a simply-expanded variable; this means
5555 @code{make} expands the text @w{@samp{$(CFLAGS) -pg}} before setting the
5556 variable. If @code{includes} is not yet defined, we get @w{@samp{ -O
5557 -pg}}, and a later definition of @code{includes} will have no effect.
5558 Conversely, by using @samp{+=} we set @code{CFLAGS} to the
5559 @emph{unexpanded} value @w{@samp{$(includes) -O -pg}}. Thus we preserve
5560 the reference to @code{includes}, so if that variable gets defined at
5561 any later point, a reference like @samp{$(CFLAGS)} still uses its
5564 @node Override Directive, Defining, Appending, Using Variables
5565 @section The @code{override} Directive
5567 @cindex overriding with @code{override}
5568 @cindex variables, overriding
5570 If a variable has been set with a command argument
5571 (@pxref{Overriding, ,Overriding Variables}),
5572 then ordinary assignments in the makefile are ignored. If you want to set
5573 the variable in the makefile even though it was set with a command
5574 argument, you can use an @code{override} directive, which is a line that
5575 looks like this:@refill
5578 override @var{variable} = @var{value}
5585 override @var{variable} := @var{value}
5588 To append more text to a variable defined on the command line, use:
5591 override @var{variable} += @var{more text}
5595 @xref{Appending, ,Appending More Text to Variables}.
5597 The @code{override} directive was not invented for escalation in the war
5598 between makefiles and command arguments. It was invented so you can alter
5599 and add to values that the user specifies with command arguments.
5601 For example, suppose you always want the @samp{-g} switch when you run the
5602 C compiler, but you would like to allow the user to specify the other
5603 switches with a command argument just as usual. You could use this
5604 @code{override} directive:
5607 override CFLAGS += -g
5610 You can also use @code{override} directives with @code{define} directives.
5611 This is done as you might expect:
5621 See the next section for information about @code{define}.
5624 @xref{Defining, ,Defining Variables Verbatim}.
5627 @node Defining, Environment, Override Directive, Using Variables
5628 @section Defining Variables Verbatim
5631 @cindex verbatim variable definition
5632 @cindex defining variables verbatim
5633 @cindex variables, defining verbatim
5635 Another way to set the value of a variable is to use the @code{define}
5636 directive. This directive has an unusual syntax which allows newline
5637 characters to be included in the value, which is convenient for defining
5638 both canned sequences of commands
5639 (@pxref{Sequences, ,Defining Canned Command Sequences}), and also
5640 sections of makefile syntax to use with @code{eval} (@pxref{Eval Function}).
5642 The @code{define} directive is followed on the same line by the name of the
5643 variable and nothing more. The value to give the variable appears on the
5644 following lines. The end of the value is marked by a line containing just
5645 the word @code{endef}. Aside from this difference in syntax, @code{define}
5646 works just like @samp{=}: it creates a recursively-expanded variable
5647 (@pxref{Flavors, ,The Two Flavors of Variables}).
5648 The variable name may contain function and variable references, which
5649 are expanded when the directive is read to find the actual variable name
5652 You may nest @code{define} directives: @code{make} will keep track of
5653 nested directives and report an error if they are not all properly
5654 closed with @code{endef}. Note that lines beginning with tab
5655 characters are considered part of a command script, so any
5656 @code{define} or @code{endef} strings appearing on such a line will
5657 not be considered @code{make} operators.
5666 The value in an ordinary assignment cannot contain a newline; but the
5667 newlines that separate the lines of the value in a @code{define} become
5668 part of the variable's value (except for the final newline which precedes
5669 the @code{endef} and is not considered part of the value).@refill
5672 When used in a command script, the previous example is functionally
5676 two-lines = echo foo; echo $(bar)
5680 since two commands separated by semicolon behave much like two separate
5681 shell commands. However, note that using two separate lines means
5682 @code{make} will invoke the shell twice, running an independent subshell
5683 for each line. @xref{Execution, ,Command Execution}.
5685 If you want variable definitions made with @code{define} to take
5686 precedence over command-line variable definitions, you can use the
5687 @code{override} directive together with @code{define}:
5690 override define two-lines
5697 @xref{Override Directive, ,The @code{override} Directive}.
5699 @node Environment, Target-specific, Defining, Using Variables
5700 @section Variables from the Environment
5702 @cindex variables, environment
5704 Variables in @code{make} can come from the environment in which
5705 @code{make} is run. Every environment variable that @code{make} sees
5706 when it starts up is transformed into a @code{make} variable with the
5707 same name and value. However, an explicit assignment in the makefile,
5708 or with a command argument, overrides the environment. (If the
5709 @samp{-e} flag is specified, then values from the environment override
5710 assignments in the makefile. @xref{Options Summary, ,Summary of
5711 Options}. But this is not recommended practice.)
5713 Thus, by setting the variable @code{CFLAGS} in your environment, you can
5714 cause all C compilations in most makefiles to use the compiler switches you
5715 prefer. This is safe for variables with standard or conventional meanings
5716 because you know that no makefile will use them for other things. (Note
5717 this is not totally reliable; some makefiles set @code{CFLAGS} explicitly
5718 and therefore are not affected by the value in the environment.)
5720 When @code{make} runs a command script, variables defined in the
5721 makefile are placed into the environment of that command. This allows
5722 you to pass values to sub-@code{make} invocations (@pxref{Recursion,
5723 ,Recursive Use of @code{make}}). By default, only variables that came
5724 from the environment or the command line are passed to recursive
5725 invocations. You can use the @code{export} directive to pass other
5726 variables. @xref{Variables/Recursion, , Communicating Variables to a
5727 Sub-@code{make}}, for full details.
5729 Other use of variables from the environment is not recommended. It is not
5730 wise for makefiles to depend for their functioning on environment variables
5731 set up outside their control, since this would cause different users to get
5732 different results from the same makefile. This is against the whole
5733 purpose of most makefiles.
5735 @cindex SHELL, import from environment
5736 Such problems would be especially likely with the variable
5737 @code{SHELL}, which is normally present in the environment to specify
5738 the user's choice of interactive shell. It would be very undesirable
5739 for this choice to affect @code{make}; so, @code{make} handles the
5740 @code{SHELL} environment variable in a special way; see @ref{Choosing
5743 @node Target-specific, Pattern-specific, Environment, Using Variables
5744 @section Target-specific Variable Values
5745 @cindex target-specific variables
5746 @cindex variables, target-specific
5748 Variable values in @code{make} are usually global; that is, they are the
5749 same regardless of where they are evaluated (unless they're reset, of
5750 course). One exception to that is automatic variables
5751 (@pxref{Automatic Variables}).
5753 The other exception is @dfn{target-specific variable values}. This
5754 feature allows you to define different values for the same variable,
5755 based on the target that @code{make} is currently building. As with
5756 automatic variables, these values are only available within the context
5757 of a target's command script (and in other target-specific assignments).
5759 Set a target-specific variable value like this:
5762 @var{target} @dots{} : @var{variable-assignment}
5769 @var{target} @dots{} : override @var{variable-assignment}
5776 @var{target} @dots{} : export @var{variable-assignment}
5779 Multiple @var{target} values create a target-specific variable value for
5780 each member of the target list individually.
5782 The @var{variable-assignment} can be any valid form of assignment;
5783 recursive (@samp{=}), static (@samp{:=}), appending (@samp{+=}), or
5784 conditional (@samp{?=}). All variables that appear within the
5785 @var{variable-assignment} are evaluated within the context of the
5786 target: thus, any previously-defined target-specific variable values
5787 will be in effect. Note that this variable is actually distinct from
5788 any ``global'' value: the two variables do not have to have the same
5789 flavor (recursive vs.@: static).
5791 Target-specific variables have the same priority as any other makefile
5792 variable. Variables provided on the command-line (and in the
5793 environment if the @samp{-e} option is in force) will take precedence.
5794 Specifying the @code{override} directive will allow the target-specific
5795 variable value to be preferred.
5797 There is one more special feature of target-specific variables: when
5798 you define a target-specific variable that variable value is also in
5799 effect for all prerequisites of this target, and all their
5800 prerequisites, etc.@: (unless those prerequisites override that variable
5801 with their own target-specific variable value). So, for example, a
5802 statement like this:
5806 prog : prog.o foo.o bar.o
5810 will set @code{CFLAGS} to @samp{-g} in the command script for
5811 @file{prog}, but it will also set @code{CFLAGS} to @samp{-g} in the
5812 command scripts that create @file{prog.o}, @file{foo.o}, and
5813 @file{bar.o}, and any command scripts which create their
5816 Be aware that a given prerequisite will only be built once per
5817 invocation of make, at most. If the same file is a prerequisite of
5818 multiple targets, and each of those targets has a different value for
5819 the same target-specific variable, then the first target to be built
5820 will cause that prerequisite to be built and the prerequisite will
5821 inherit the target-specific value from the first target. It will
5822 ignore the target-specific values from any other targets.
5824 @node Pattern-specific, , Target-specific, Using Variables
5825 @section Pattern-specific Variable Values
5826 @cindex pattern-specific variables
5827 @cindex variables, pattern-specific
5829 In addition to target-specific variable values
5830 (@pxref{Target-specific, ,Target-specific Variable Values}), GNU
5831 @code{make} supports pattern-specific variable values. In this form,
5832 the variable is defined for any target that matches the pattern
5833 specified. If a target matches more than one pattern, all the
5834 matching pattern-specific variables are interpreted in the order in
5835 which they were defined in the makefile, and collected together into
5836 one set. Variables defined in this way are searched after any
5837 target-specific variables defined explicitly for that target, and
5838 before target-specific variables defined for the parent target.
5840 Set a pattern-specific variable value like this:
5843 @var{pattern} @dots{} : @var{variable-assignment}
5850 @var{pattern} @dots{} : override @var{variable-assignment}
5854 where @var{pattern} is a %-pattern. As with target-specific variable
5855 values, multiple @var{pattern} values create a pattern-specific variable
5856 value for each pattern individually. The @var{variable-assignment} can
5857 be any valid form of assignment. Any command-line variable setting will
5858 take precedence, unless @code{override} is specified.
5867 will assign @code{CFLAGS} the value of @samp{-O} for all targets
5868 matching the pattern @code{%.o}.
5870 @node Conditionals, Functions, Using Variables, Top
5871 @chapter Conditional Parts of Makefiles
5873 @cindex conditionals
5874 A @dfn{conditional} causes part of a makefile to be obeyed or ignored
5875 depending on the values of variables. Conditionals can compare the
5876 value of one variable to another, or the value of a variable to
5877 a constant string. Conditionals control what @code{make} actually
5878 ``sees'' in the makefile, so they @emph{cannot} be used to control shell
5879 commands at the time of execution.@refill
5882 * Conditional Example:: Example of a conditional
5883 * Conditional Syntax:: The syntax of conditionals.
5884 * Testing Flags:: Conditionals that test flags.
5887 @node Conditional Example, Conditional Syntax, Conditionals, Conditionals
5888 @section Example of a Conditional
5890 The following example of a conditional tells @code{make} to use one set
5891 of libraries if the @code{CC} variable is @samp{gcc}, and a different
5892 set of libraries otherwise. It works by controlling which of two
5893 command lines will be used as the command for a rule. The result is
5894 that @samp{CC=gcc} as an argument to @code{make} changes not only which
5895 compiler is used but also which libraries are linked.
5898 libs_for_gcc = -lgnu
5903 $(CC) -o foo $(objects) $(libs_for_gcc)
5905 $(CC) -o foo $(objects) $(normal_libs)
5909 This conditional uses three directives: one @code{ifeq}, one @code{else}
5910 and one @code{endif}.
5912 The @code{ifeq} directive begins the conditional, and specifies the
5913 condition. It contains two arguments, separated by a comma and surrounded
5914 by parentheses. Variable substitution is performed on both arguments and
5915 then they are compared. The lines of the makefile following the
5916 @code{ifeq} are obeyed if the two arguments match; otherwise they are
5919 The @code{else} directive causes the following lines to be obeyed if the
5920 previous conditional failed. In the example above, this means that the
5921 second alternative linking command is used whenever the first alternative
5922 is not used. It is optional to have an @code{else} in a conditional.
5924 The @code{endif} directive ends the conditional. Every conditional must
5925 end with an @code{endif}. Unconditional makefile text follows.
5927 As this example illustrates, conditionals work at the textual level:
5928 the lines of the conditional are treated as part of the makefile, or
5929 ignored, according to the condition. This is why the larger syntactic
5930 units of the makefile, such as rules, may cross the beginning or the
5931 end of the conditional.
5933 When the variable @code{CC} has the value @samp{gcc}, the above example has
5938 $(CC) -o foo $(objects) $(libs_for_gcc)
5942 When the variable @code{CC} has any other value, the effect is this:
5946 $(CC) -o foo $(objects) $(normal_libs)
5949 Equivalent results can be obtained in another way by conditionalizing a
5950 variable assignment and then using the variable unconditionally:
5953 libs_for_gcc = -lgnu
5957 libs=$(libs_for_gcc)
5963 $(CC) -o foo $(objects) $(libs)
5966 @node Conditional Syntax, Testing Flags, Conditional Example, Conditionals
5967 @section Syntax of Conditionals
5975 The syntax of a simple conditional with no @code{else} is as follows:
5978 @var{conditional-directive}
5984 The @var{text-if-true} may be any lines of text, to be considered as part
5985 of the makefile if the condition is true. If the condition is false, no
5986 text is used instead.
5988 The syntax of a complex conditional is as follows:
5991 @var{conditional-directive}
6001 @var{conditional-directive}
6002 @var{text-if-one-is-true}
6003 else @var{conditional-directive}
6011 There can be as many ``@code{else} @var{conditional-directive}''
6012 clauses as necessary. Once a given condition is true,
6013 @var{text-if-true} is used and no other clause is used; if no
6014 condition is true then @var{text-if-false} is used. The
6015 @var{text-if-true} and @var{text-if-false} can be any number of lines
6018 The syntax of the @var{conditional-directive} is the same whether the
6019 conditional is simple or complex; after an @code{else} or not. There
6020 are four different directives that test different conditions. Here is
6024 @item ifeq (@var{arg1}, @var{arg2})
6025 @itemx ifeq '@var{arg1}' '@var{arg2}'
6026 @itemx ifeq "@var{arg1}" "@var{arg2}"
6027 @itemx ifeq "@var{arg1}" '@var{arg2}'
6028 @itemx ifeq '@var{arg1}' "@var{arg2}"
6029 Expand all variable references in @var{arg1} and @var{arg2} and
6030 compare them. If they are identical, the @var{text-if-true} is
6031 effective; otherwise, the @var{text-if-false}, if any, is effective.
6033 Often you want to test if a variable has a non-empty value. When the
6034 value results from complex expansions of variables and functions,
6035 expansions you would consider empty may actually contain whitespace
6036 characters and thus are not seen as empty. However, you can use the
6037 @code{strip} function (@pxref{Text Functions}) to avoid interpreting
6038 whitespace as a non-empty value. For example:
6042 ifeq ($(strip $(foo)),)
6049 will evaluate @var{text-if-empty} even if the expansion of
6050 @code{$(foo)} contains whitespace characters.
6052 @item ifneq (@var{arg1}, @var{arg2})
6053 @itemx ifneq '@var{arg1}' '@var{arg2}'
6054 @itemx ifneq "@var{arg1}" "@var{arg2}"
6055 @itemx ifneq "@var{arg1}" '@var{arg2}'
6056 @itemx ifneq '@var{arg1}' "@var{arg2}"
6057 Expand all variable references in @var{arg1} and @var{arg2} and
6058 compare them. If they are different, the @var{text-if-true} is
6059 effective; otherwise, the @var{text-if-false}, if any, is effective.
6061 @item ifdef @var{variable-name}
6062 The @code{ifdef} form takes the @emph{name} of a variable as its
6063 argument, not a reference to a variable. The value of that variable
6064 has a non-empty value, the @var{text-if-true} is effective; otherwise,
6065 the @var{text-if-false}, if any, is effective. Variables that have
6066 never been defined have an empty value. The text @var{variable-name}
6067 is expanded, so it could be a variable or function that expands
6068 to the name of a variable. For example:
6078 The variable reference @code{$(foo)} is expanded, yielding @code{bar},
6079 which is considered to be the name of a variable. The variable
6080 @code{bar} is not expanded, but its value is examined to determine if
6083 Note that @code{ifdef} only tests whether a variable has a value. It
6084 does not expand the variable to see if that value is nonempty.
6085 Consequently, tests using @code{ifdef} return true for all definitions
6086 except those like @code{foo =}. To test for an empty value, use
6087 @w{@code{ifeq ($(foo),)}}. For example,
6100 sets @samp{frobozz} to @samp{yes}, while:
6112 sets @samp{frobozz} to @samp{no}.
6114 @item ifndef @var{variable-name}
6115 If the variable @var{variable-name} has an empty value, the
6116 @var{text-if-true} is effective; otherwise, the @var{text-if-false},
6117 if any, is effective. The rules for expansion and testing of
6118 @var{variable-name} are identical to the @code{ifdef} directive.
6121 Extra spaces are allowed and ignored at the beginning of the conditional
6122 directive line, but a tab is not allowed. (If the line begins with a tab,
6123 it will be considered a command for a rule.) Aside from this, extra spaces
6124 or tabs may be inserted with no effect anywhere except within the directive
6125 name or within an argument. A comment starting with @samp{#} may appear at
6126 the end of the line.
6128 The other two directives that play a part in a conditional are @code{else}
6129 and @code{endif}. Each of these directives is written as one word, with no
6130 arguments. Extra spaces are allowed and ignored at the beginning of the
6131 line, and spaces or tabs at the end. A comment starting with @samp{#} may
6132 appear at the end of the line.
6134 Conditionals affect which lines of the makefile @code{make} uses. If
6135 the condition is true, @code{make} reads the lines of the
6136 @var{text-if-true} as part of the makefile; if the condition is false,
6137 @code{make} ignores those lines completely. It follows that syntactic
6138 units of the makefile, such as rules, may safely be split across the
6139 beginning or the end of the conditional.@refill
6141 @code{make} evaluates conditionals when it reads a makefile.
6142 Consequently, you cannot use automatic variables in the tests of
6143 conditionals because they are not defined until commands are run
6144 (@pxref{Automatic Variables}).
6146 To prevent intolerable confusion, it is not permitted to start a
6147 conditional in one makefile and end it in another. However, you may
6148 write an @code{include} directive within a conditional, provided you do
6149 not attempt to terminate the conditional inside the included file.
6151 @node Testing Flags, , Conditional Syntax, Conditionals
6152 @section Conditionals that Test Flags
6154 You can write a conditional that tests @code{make} command flags such as
6155 @samp{-t} by using the variable @code{MAKEFLAGS} together with the
6156 @code{findstring} function
6157 (@pxref{Text Functions, , Functions for String Substitution and Analysis}).
6158 This is useful when @code{touch} is not enough to make a file appear up
6161 The @code{findstring} function determines whether one string appears as a
6162 substring of another. If you want to test for the @samp{-t} flag,
6163 use @samp{t} as the first string and the value of @code{MAKEFLAGS} as
6166 For example, here is how to arrange to use @samp{ranlib -t} to finish
6167 marking an archive file up to date:
6171 ifneq (,$(findstring t,$(MAKEFLAGS)))
6173 +ranlib -t archive.a
6180 The @samp{+} prefix marks those command lines as ``recursive'' so
6181 that they will be executed despite use of the @samp{-t} flag.
6182 @xref{Recursion, ,Recursive Use of @code{make}}.
6184 @node Functions, Running, Conditionals, Top
6185 @chapter Functions for Transforming Text
6188 @dfn{Functions} allow you to do text processing in the makefile to compute
6189 the files to operate on or the commands to use. You use a function in a
6190 @dfn{function call}, where you give the name of the function and some text
6191 (the @dfn{arguments}) for the function to operate on. The result of the
6192 function's processing is substituted into the makefile at the point of the
6193 call, just as a variable might be substituted.
6196 * Syntax of Functions:: How to write a function call.
6197 * Text Functions:: General-purpose text manipulation functions.
6198 * File Name Functions:: Functions for manipulating file names.
6199 * Conditional Functions:: Functions that implement conditions.
6200 * Foreach Function:: Repeat some text with controlled variation.
6201 * Call Function:: Expand a user-defined function.
6202 * Value Function:: Return the un-expanded value of a variable.
6203 * Eval Function:: Evaluate the arguments as makefile syntax.
6204 * Origin Function:: Find where a variable got its value.
6205 * Flavor Function:: Find out the flavor of a variable.
6206 * Shell Function:: Substitute the output of a shell command.
6207 * Make Control Functions:: Functions that control how make runs.
6210 @node Syntax of Functions, Text Functions, Functions, Functions
6211 @section Function Call Syntax
6212 @cindex @code{$}, in function call
6213 @cindex dollar sign (@code{$}), in function call
6214 @cindex arguments of functions
6215 @cindex functions, syntax of
6217 A function call resembles a variable reference. It looks like this:
6220 $(@var{function} @var{arguments})
6227 $@{@var{function} @var{arguments}@}
6230 Here @var{function} is a function name; one of a short list of names
6231 that are part of @code{make}. You can also essentially create your own
6232 functions by using the @code{call} builtin function.
6234 The @var{arguments} are the arguments of the function. They are
6235 separated from the function name by one or more spaces or tabs, and if
6236 there is more than one argument, then they are separated by commas.
6237 Such whitespace and commas are not part of an argument's value. The
6238 delimiters which you use to surround the function call, whether
6239 parentheses or braces, can appear in an argument only in matching pairs;
6240 the other kind of delimiters may appear singly. If the arguments
6241 themselves contain other function calls or variable references, it is
6242 wisest to use the same kind of delimiters for all the references; write
6243 @w{@samp{$(subst a,b,$(x))}}, not @w{@samp{$(subst a,b,$@{x@})}}. This
6244 is because it is clearer, and because only one type of delimiter is
6245 matched to find the end of the reference.
6247 The text written for each argument is processed by substitution of
6248 variables and function calls to produce the argument value, which
6249 is the text on which the function acts. The substitution is done in the
6250 order in which the arguments appear.
6252 Commas and unmatched parentheses or braces cannot appear in the text of an
6253 argument as written; leading spaces cannot appear in the text of the first
6254 argument as written. These characters can be put into the argument value
6255 by variable substitution. First define variables @code{comma} and
6256 @code{space} whose values are isolated comma and space characters, then
6257 substitute these variables where such characters are wanted, like this:
6263 space:= $(empty) $(empty)
6265 bar:= $(subst $(space),$(comma),$(foo))
6266 # @r{bar is now `a,b,c'.}
6271 Here the @code{subst} function replaces each space with a comma, through
6272 the value of @code{foo}, and substitutes the result.
6274 @node Text Functions, File Name Functions, Syntax of Functions, Functions
6275 @section Functions for String Substitution and Analysis
6276 @cindex functions, for text
6278 Here are some functions that operate on strings:
6281 @item $(subst @var{from},@var{to},@var{text})
6283 Performs a textual replacement on the text @var{text}: each occurrence
6284 of @var{from} is replaced by @var{to}. The result is substituted for
6285 the function call. For example,
6288 $(subst ee,EE,feet on the street)
6291 substitutes the string @samp{fEEt on the strEEt}.
6293 @item $(patsubst @var{pattern},@var{replacement},@var{text})
6295 Finds whitespace-separated words in @var{text} that match
6296 @var{pattern} and replaces them with @var{replacement}. Here
6297 @var{pattern} may contain a @samp{%} which acts as a wildcard,
6298 matching any number of any characters within a word. If
6299 @var{replacement} also contains a @samp{%}, the @samp{%} is replaced
6300 by the text that matched the @samp{%} in @var{pattern}. Only the first
6301 @samp{%} in the @var{pattern} and @var{replacement} is treated this
6302 way; any subsequent @samp{%} is unchanged.@refill
6304 @cindex @code{%}, quoting in @code{patsubst}
6305 @cindex @code{%}, quoting with @code{\} (backslash)
6306 @cindex @code{\} (backslash), to quote @code{%}
6307 @cindex backslash (@code{\}), to quote @code{%}
6308 @cindex quoting @code{%}, in @code{patsubst}
6309 @samp{%} characters in @code{patsubst} function invocations can be
6310 quoted with preceding backslashes (@samp{\}). Backslashes that would
6311 otherwise quote @samp{%} characters can be quoted with more backslashes.
6312 Backslashes that quote @samp{%} characters or other backslashes are
6313 removed from the pattern before it is compared file names or has a stem
6314 substituted into it. Backslashes that are not in danger of quoting
6315 @samp{%} characters go unmolested. For example, the pattern
6316 @file{the\%weird\\%pattern\\} has @samp{the%weird\} preceding the
6317 operative @samp{%} character, and @samp{pattern\\} following it. The
6318 final two backslashes are left alone because they cannot affect any
6319 @samp{%} character.@refill
6321 Whitespace between words is folded into single space characters;
6322 leading and trailing whitespace is discarded.
6327 $(patsubst %.c,%.o,x.c.c bar.c)
6331 produces the value @samp{x.c.o bar.o}.
6333 Substitution references (@pxref{Substitution Refs, ,Substitution
6334 References}) are a simpler way to get the effect of the @code{patsubst}
6338 $(@var{var}:@var{pattern}=@var{replacement})
6345 $(patsubst @var{pattern},@var{replacement},$(@var{var}))
6348 The second shorthand simplifies one of the most common uses of
6349 @code{patsubst}: replacing the suffix at the end of file names.
6352 $(@var{var}:@var{suffix}=@var{replacement})
6359 $(patsubst %@var{suffix},%@var{replacement},$(@var{var}))
6363 For example, you might have a list of object files:
6366 objects = foo.o bar.o baz.o
6370 To get the list of corresponding source files, you could simply write:
6377 instead of using the general form:
6380 $(patsubst %.o,%.c,$(objects))
6383 @item $(strip @var{string})
6384 @cindex stripping whitespace
6385 @cindex whitespace, stripping
6386 @cindex spaces, stripping
6388 Removes leading and trailing whitespace from @var{string} and replaces
6389 each internal sequence of one or more whitespace characters with a
6390 single space. Thus, @samp{$(strip a b c )} results in @w{@samp{a b c}}.
6392 The function @code{strip} can be very useful when used in conjunction
6393 with conditionals. When comparing something with the empty string
6394 @samp{} using @code{ifeq} or @code{ifneq}, you usually want a string of
6395 just whitespace to match the empty string (@pxref{Conditionals}).
6397 Thus, the following may fail to have the desired results:
6401 ifneq "$(needs_made)" ""
6404 all:;@@echo 'Nothing to make!'
6409 Replacing the variable reference @w{@samp{$(needs_made)}} with the
6410 function call @w{@samp{$(strip $(needs_made))}} in the @code{ifneq}
6411 directive would make it more robust.@refill
6413 @item $(findstring @var{find},@var{in})
6415 @cindex searching for strings
6416 @cindex finding strings
6417 @cindex strings, searching for
6418 Searches @var{in} for an occurrence of @var{find}. If it occurs, the
6419 value is @var{find}; otherwise, the value is empty. You can use this
6420 function in a conditional to test for the presence of a specific
6421 substring in a given string. Thus, the two examples,
6424 $(findstring a,a b c)
6429 produce the values @samp{a} and @samp{} (the empty string),
6430 respectively. @xref{Testing Flags}, for a practical application of
6431 @code{findstring}.@refill
6435 @cindex filtering words
6436 @cindex words, filtering
6437 @item $(filter @var{pattern}@dots{},@var{text})
6438 Returns all whitespace-separated words in @var{text} that @emph{do} match
6439 any of the @var{pattern} words, removing any words that @emph{do not}
6440 match. The patterns are written using @samp{%}, just like the patterns
6441 used in the @code{patsubst} function above.@refill
6443 The @code{filter} function can be used to separate out different types
6444 of strings (such as file names) in a variable. For example:
6447 sources := foo.c bar.c baz.s ugh.h
6449 cc $(filter %.c %.s,$(sources)) -o foo
6453 says that @file{foo} depends of @file{foo.c}, @file{bar.c},
6454 @file{baz.s} and @file{ugh.h} but only @file{foo.c}, @file{bar.c} and
6455 @file{baz.s} should be specified in the command to the
6458 @item $(filter-out @var{pattern}@dots{},@var{text})
6460 @cindex filtering out words
6461 @cindex words, filtering out
6462 Returns all whitespace-separated words in @var{text} that @emph{do not}
6463 match any of the @var{pattern} words, removing the words that @emph{do}
6464 match one or more. This is the exact opposite of the @code{filter}
6471 objects=main1.o foo.o main2.o bar.o
6472 mains=main1.o main2.o
6477 the following generates a list which contains all the object files not
6481 $(filter-out $(mains),$(objects))
6486 @cindex sorting words
6487 @item $(sort @var{list})
6488 Sorts the words of @var{list} in lexical order, removing duplicate
6489 words. The output is a list of words separated by single spaces.
6493 $(sort foo bar lose)
6497 returns the value @samp{bar foo lose}.
6499 @cindex removing duplicate words
6500 @cindex duplicate words, removing
6501 @cindex words, removing duplicates
6502 Incidentally, since @code{sort} removes duplicate words, you can use
6503 it for this purpose even if you don't care about the sort order.
6505 @item $(word @var{n},@var{text})
6507 @cindex word, selecting a
6508 @cindex selecting a word
6509 Returns the @var{n}th word of @var{text}. The legitimate values of
6510 @var{n} start from 1. If @var{n} is bigger than the number of words
6511 in @var{text}, the value is empty. For example,
6514 $(word 2, foo bar baz)
6520 @item $(wordlist @var{s},@var{e},@var{text})
6522 @cindex words, selecting lists of
6523 @cindex selecting word lists
6524 Returns the list of words in @var{text} starting with word @var{s} and
6525 ending with word @var{e} (inclusive). The legitimate values of @var{s}
6526 start from 1; @var{e} may start from 0. If @var{s} is bigger than the
6527 number of words in @var{text}, the value is empty. If @var{e} is
6528 bigger than the number of words in @var{text}, words up to the end of
6529 @var{text} are returned. If @var{s} is greater than @var{e}, nothing
6530 is returned. For example,
6533 $(wordlist 2, 3, foo bar baz)
6537 returns @samp{bar baz}.
6539 @c Following item phrased to prevent overfull hbox. --RJC 17 Jul 92
6540 @item $(words @var{text})
6542 @cindex words, finding number
6543 Returns the number of words in @var{text}.
6544 Thus, the last word of @var{text} is
6545 @w{@code{$(word $(words @var{text}),@var{text})}}.@refill
6547 @item $(firstword @var{names}@dots{})
6549 @cindex words, extracting first
6550 The argument @var{names} is regarded as a series of names, separated
6551 by whitespace. The value is the first name in the series. The rest
6552 of the names are ignored.
6557 $(firstword foo bar)
6561 produces the result @samp{foo}. Although @code{$(firstword
6562 @var{text})} is the same as @code{$(word 1,@var{text})}, the
6563 @code{firstword} function is retained for its simplicity.@refill
6566 @item $(lastword @var{names}@dots{})
6568 @cindex words, extracting last
6569 The argument @var{names} is regarded as a series of names, separated
6570 by whitespace. The value is the last name in the series.
6579 produces the result @samp{bar}. Although @code{$(lastword
6580 @var{text})} is the same as @code{$(word $(words @var{text}),@var{text})},
6581 the @code{lastword} function was added for its simplicity and better
6586 Here is a realistic example of the use of @code{subst} and
6587 @code{patsubst}. Suppose that a makefile uses the @code{VPATH} variable
6588 to specify a list of directories that @code{make} should search for
6590 (@pxref{General Search, , @code{VPATH} Search Path for All Prerequisites}).
6591 This example shows how to
6592 tell the C compiler to search for header files in the same list of
6595 The value of @code{VPATH} is a list of directories separated by colons,
6596 such as @samp{src:../headers}. First, the @code{subst} function is used to
6597 change the colons to spaces:
6600 $(subst :, ,$(VPATH))
6604 This produces @samp{src ../headers}. Then @code{patsubst} is used to turn
6605 each directory name into a @samp{-I} flag. These can be added to the
6606 value of the variable @code{CFLAGS}, which is passed automatically to the C
6607 compiler, like this:
6610 override CFLAGS += $(patsubst %,-I%,$(subst :, ,$(VPATH)))
6614 The effect is to append the text @samp{-Isrc -I../headers} to the
6615 previously given value of @code{CFLAGS}. The @code{override} directive is
6616 used so that the new value is assigned even if the previous value of
6617 @code{CFLAGS} was specified with a command argument (@pxref{Override
6618 Directive, , The @code{override} Directive}).
6620 @node File Name Functions, Conditional Functions, Text Functions, Functions
6621 @section Functions for File Names
6622 @cindex functions, for file names
6623 @cindex file name functions
6625 Several of the built-in expansion functions relate specifically to
6626 taking apart file names or lists of file names.
6628 Each of the following functions performs a specific transformation on a
6629 file name. The argument of the function is regarded as a series of file
6630 names, separated by whitespace. (Leading and trailing whitespace is
6631 ignored.) Each file name in the series is transformed in the same way and
6632 the results are concatenated with single spaces between them.
6635 @item $(dir @var{names}@dots{})
6637 @cindex directory part
6638 @cindex file name, directory part
6639 Extracts the directory-part of each file name in @var{names}. The
6640 directory-part of the file name is everything up through (and
6641 including) the last slash in it. If the file name contains no slash,
6642 the directory part is the string @samp{./}. For example,
6645 $(dir src/foo.c hacks)
6649 produces the result @samp{src/ ./}.
6651 @item $(notdir @var{names}@dots{})
6653 @cindex file name, nondirectory part
6654 @cindex nondirectory part
6655 Extracts all but the directory-part of each file name in @var{names}.
6656 If the file name contains no slash, it is left unchanged. Otherwise,
6657 everything through the last slash is removed from it.
6659 A file name that ends with a slash becomes an empty string. This is
6660 unfortunate, because it means that the result does not always have the
6661 same number of whitespace-separated file names as the argument had;
6662 but we do not see any other valid alternative.
6667 $(notdir src/foo.c hacks)
6671 produces the result @samp{foo.c hacks}.
6673 @item $(suffix @var{names}@dots{})
6675 @cindex suffix, function to find
6676 @cindex file name suffix
6677 Extracts the suffix of each file name in @var{names}. If the file name
6678 contains a period, the suffix is everything starting with the last
6679 period. Otherwise, the suffix is the empty string. This frequently
6680 means that the result will be empty when @var{names} is not, and if
6681 @var{names} contains multiple file names, the result may contain fewer
6687 $(suffix src/foo.c src-1.0/bar.c hacks)
6691 produces the result @samp{.c .c}.
6693 @item $(basename @var{names}@dots{})
6696 @cindex file name, basename of
6697 Extracts all but the suffix of each file name in @var{names}. If the
6698 file name contains a period, the basename is everything starting up to
6699 (and not including) the last period. Periods in the directory part are
6700 ignored. If there is no period, the basename is the entire file name.
6704 $(basename src/foo.c src-1.0/bar hacks)
6708 produces the result @samp{src/foo src-1.0/bar hacks}.
6710 @c plural convention with dots (be consistent)
6711 @item $(addsuffix @var{suffix},@var{names}@dots{})
6713 @cindex suffix, adding
6714 @cindex file name suffix, adding
6715 The argument @var{names} is regarded as a series of names, separated
6716 by whitespace; @var{suffix} is used as a unit. The value of
6717 @var{suffix} is appended to the end of each individual name and the
6718 resulting larger names are concatenated with single spaces between
6722 $(addsuffix .c,foo bar)
6726 produces the result @samp{foo.c bar.c}.
6728 @item $(addprefix @var{prefix},@var{names}@dots{})
6730 @cindex prefix, adding
6731 @cindex file name prefix, adding
6732 The argument @var{names} is regarded as a series of names, separated
6733 by whitespace; @var{prefix} is used as a unit. The value of
6734 @var{prefix} is prepended to the front of each individual name and the
6735 resulting larger names are concatenated with single spaces between
6739 $(addprefix src/,foo bar)
6743 produces the result @samp{src/foo src/bar}.
6745 @item $(join @var{list1},@var{list2})
6747 @cindex joining lists of words
6748 @cindex words, joining lists
6749 Concatenates the two arguments word by word: the two first words (one
6750 from each argument) concatenated form the first word of the result, the
6751 two second words form the second word of the result, and so on. So the
6752 @var{n}th word of the result comes from the @var{n}th word of each
6753 argument. If one argument has more words that the other, the extra
6754 words are copied unchanged into the result.
6756 For example, @samp{$(join a b,.c .o)} produces @samp{a.c b.o}.
6758 Whitespace between the words in the lists is not preserved; it is
6759 replaced with a single space.
6761 This function can merge the results of the @code{dir} and
6762 @code{notdir} functions, to produce the original list of files which
6763 was given to those two functions.@refill
6765 @item $(wildcard @var{pattern})
6767 @cindex wildcard, function
6768 The argument @var{pattern} is a file name pattern, typically containing
6769 wildcard characters (as in shell file name patterns). The result of
6770 @code{wildcard} is a space-separated list of the names of existing files
6771 that match the pattern.
6772 @xref{Wildcards, ,Using Wildcard Characters in File Names}.
6774 @item $(realpath @var{names}@dots{})
6777 @cindex file name, realpath of
6778 For each file name in @var{names} return the canonical absolute name.
6779 A canonical name does not contain any @code{.} or @code{..} components,
6780 nor any repeated path separators (@code{/}) or symlinks. In case of a
6781 failure the empty string is returned. Consult the @code{realpath(3)}
6782 documentation for a list of possible failure causes.
6784 @item $(abspath @var{names}@dots{})
6787 @cindex file name, abspath of
6788 For each file name in @var{names} return an absolute name that does
6789 not contain any @code{.} or @code{..} components, nor any repeated path
6790 separators (@code{/}). Note that, in contrast to @code{realpath}
6791 function, @code{abspath} does not resolve symlinks and does not require
6792 the file names to refer to an existing file or directory. Use the
6793 @code{wildcard} function to test for existence.
6796 @node Conditional Functions, Foreach Function, File Name Functions, Functions
6797 @section Functions for Conditionals
6799 @cindex conditional expansion
6800 There are three functions that provide conditional expansion. A key
6801 aspect of these functions is that not all of the arguments are
6802 expanded initially. Only those arguments which need to be expanded,
6806 @item $(if @var{condition},@var{then-part}[,@var{else-part}])
6808 The @code{if} function provides support for conditional expansion in a
6809 functional context (as opposed to the GNU @code{make} makefile
6810 conditionals such as @code{ifeq} (@pxref{Conditional Syntax, ,Syntax of
6813 The first argument, @var{condition}, first has all preceding and
6814 trailing whitespace stripped, then is expanded. If it expands to any
6815 non-empty string, then the condition is considered to be true. If it
6816 expands to an empty string, the condition is considered to be false.
6818 If the condition is true then the second argument, @var{then-part}, is
6819 evaluated and this is used as the result of the evaluation of the entire
6822 If the condition is false then the third argument, @var{else-part}, is
6823 evaluated and this is the result of the @code{if} function. If there is
6824 no third argument, the @code{if} function evaluates to nothing (the
6827 Note that only one of the @var{then-part} or the @var{else-part} will be
6828 evaluated, never both. Thus, either can contain side-effects (such as
6829 @code{shell} function calls, etc.)
6831 @item $(or @var{condition1}[,@var{condition2}[,@var{condition3}@dots{}]])
6833 The @code{or} function provides a ``short-circuiting'' OR operation.
6834 Each argument is expanded, in order. If an argument expands to a
6835 non-empty string the processing stops and the result of the expansion
6836 is that string. If, after all arguments are expanded, all of them are
6837 false (empty), then the result of the expansion is the empty string.
6839 @item $(and @var{condition1}[,@var{condition2}[,@var{condition3}@dots{}]])
6841 The @code{and} function provides a ``short-circuiting'' AND operation.
6842 Each argument is expanded, in order. If an argument expands to an
6843 empty string the processing stops and the result of the expansion is
6844 the empty string. If all arguments expand to a non-empty string then
6845 the result of the expansion is the expansion of the last argument.
6849 @node Foreach Function, Call Function, Conditional Functions, Functions
6850 @section The @code{foreach} Function
6852 @cindex words, iterating over
6854 The @code{foreach} function is very different from other functions. It
6855 causes one piece of text to be used repeatedly, each time with a different
6856 substitution performed on it. It resembles the @code{for} command in the
6857 shell @code{sh} and the @code{foreach} command in the C-shell @code{csh}.
6859 The syntax of the @code{foreach} function is:
6862 $(foreach @var{var},@var{list},@var{text})
6866 The first two arguments, @var{var} and @var{list}, are expanded before
6867 anything else is done; note that the last argument, @var{text}, is
6868 @strong{not} expanded at the same time. Then for each word of the expanded
6869 value of @var{list}, the variable named by the expanded value of @var{var}
6870 is set to that word, and @var{text} is expanded. Presumably @var{text}
6871 contains references to that variable, so its expansion will be different
6874 The result is that @var{text} is expanded as many times as there are
6875 whitespace-separated words in @var{list}. The multiple expansions of
6876 @var{text} are concatenated, with spaces between them, to make the result
6879 This simple example sets the variable @samp{files} to the list of all files
6880 in the directories in the list @samp{dirs}:
6884 files := $(foreach dir,$(dirs),$(wildcard $(dir)/*))
6887 Here @var{text} is @samp{$(wildcard $(dir)/*)}. The first repetition
6888 finds the value @samp{a} for @code{dir}, so it produces the same result
6889 as @samp{$(wildcard a/*)}; the second repetition produces the result
6890 of @samp{$(wildcard b/*)}; and the third, that of @samp{$(wildcard c/*)}.
6892 This example has the same result (except for setting @samp{dirs}) as
6893 the following example:
6896 files := $(wildcard a/* b/* c/* d/*)
6899 When @var{text} is complicated, you can improve readability by giving it
6900 a name, with an additional variable:
6903 find_files = $(wildcard $(dir)/*)
6905 files := $(foreach dir,$(dirs),$(find_files))
6909 Here we use the variable @code{find_files} this way. We use plain @samp{=}
6910 to define a recursively-expanding variable, so that its value contains an
6911 actual function call to be reexpanded under the control of @code{foreach};
6912 a simply-expanded variable would not do, since @code{wildcard} would be
6913 called only once at the time of defining @code{find_files}.
6915 The @code{foreach} function has no permanent effect on the variable
6916 @var{var}; its value and flavor after the @code{foreach} function call are
6917 the same as they were beforehand. The other values which are taken from
6918 @var{list} are in effect only temporarily, during the execution of
6919 @code{foreach}. The variable @var{var} is a simply-expanded variable
6920 during the execution of @code{foreach}. If @var{var} was undefined
6921 before the @code{foreach} function call, it is undefined after the call.
6922 @xref{Flavors, ,The Two Flavors of Variables}.@refill
6924 You must take care when using complex variable expressions that result in
6925 variable names because many strange things are valid variable names, but
6926 are probably not what you intended. For example,
6929 files := $(foreach Esta escrito en espanol!,b c ch,$(find_files))
6933 might be useful if the value of @code{find_files} references the variable
6934 whose name is @samp{Esta escrito en espanol!} (es un nombre bastante largo,
6935 no?), but it is more likely to be a mistake.
6937 @node Call Function, Value Function, Foreach Function, Functions
6938 @section The @code{call} Function
6940 @cindex functions, user defined
6941 @cindex user defined functions
6943 The @code{call} function is unique in that it can be used to create new
6944 parameterized functions. You can write a complex expression as the
6945 value of a variable, then use @code{call} to expand it with different
6948 The syntax of the @code{call} function is:
6951 $(call @var{variable},@var{param},@var{param},@dots{})
6954 When @code{make} expands this function, it assigns each @var{param} to
6955 temporary variables @code{$(1)}, @code{$(2)}, etc. The variable
6956 @code{$(0)} will contain @var{variable}. There is no maximum number of
6957 parameter arguments. There is no minimum, either, but it doesn't make
6958 sense to use @code{call} with no parameters.
6960 Then @var{variable} is expanded as a @code{make} variable in the context
6961 of these temporary assignments. Thus, any reference to @code{$(1)} in
6962 the value of @var{variable} will resolve to the first @var{param} in the
6963 invocation of @code{call}.
6965 Note that @var{variable} is the @emph{name} of a variable, not a
6966 @emph{reference} to that variable. Therefore you would not normally use
6967 a @samp{$} or parentheses when writing it. (You can, however, use a
6968 variable reference in the name if you want the name not to be a
6971 If @var{variable} is the name of a builtin function, the builtin function
6972 is always invoked (even if a @code{make} variable by that name also
6975 The @code{call} function expands the @var{param} arguments before
6976 assigning them to temporary variables. This means that @var{variable}
6977 values containing references to builtin functions that have special
6978 expansion rules, like @code{foreach} or @code{if}, may not work as you
6981 Some examples may make this clearer.
6983 This macro simply reverses its arguments:
6988 foo = $(call reverse,a,b)
6992 Here @var{foo} will contain @samp{b a}.
6994 This one is slightly more interesting: it defines a macro to search for
6995 the first instance of a program in @code{PATH}:
6998 pathsearch = $(firstword $(wildcard $(addsuffix /$(1),$(subst :, ,$(PATH)))))
7000 LS := $(call pathsearch,ls)
7004 Now the variable LS contains @code{/bin/ls} or similar.
7006 The @code{call} function can be nested. Each recursive invocation gets
7007 its own local values for @code{$(1)}, etc.@: that mask the values of
7008 higher-level @code{call}. For example, here is an implementation of a
7012 map = $(foreach a,$(2),$(call $(1),$(a)))
7015 Now you can @var{map} a function that normally takes only one argument,
7016 such as @code{origin}, to multiple values in one step:
7019 o = $(call map,origin,o map MAKE)
7022 and end up with @var{o} containing something like @samp{file file default}.
7024 A final caution: be careful when adding whitespace to the arguments to
7025 @code{call}. As with other functions, any whitespace contained in the
7026 second and subsequent arguments is kept; this can cause strange
7027 effects. It's generally safest to remove all extraneous whitespace when
7028 providing parameters to @code{call}.
7030 @node Value Function, Eval Function, Call Function, Functions
7031 @comment node-name, next, previous, up
7032 @section The @code{value} Function
7034 @cindex variables, unexpanded value
7036 The @code{value} function provides a way for you to use the value of a
7037 variable @emph{without} having it expanded. Please note that this
7038 does not undo expansions which have already occurred; for example if
7039 you create a simply expanded variable its value is expanded during the
7040 definition; in that case the @code{value} function will return the
7041 same result as using the variable directly.
7043 The syntax of the @code{value} function is:
7046 $(value @var{variable})
7049 Note that @var{variable} is the @emph{name} of a variable; not a
7050 @emph{reference} to that variable. Therefore you would not normally
7051 use a @samp{$} or parentheses when writing it. (You can, however, use
7052 a variable reference in the name if you want the name not to be a
7055 The result of this function is a string containing the value of
7056 @var{variable}, without any expansion occurring. For example, in this
7070 The first output line would be @code{ATH}, since the ``$P'' would be
7071 expanded as a @code{make} variable, while the second output line would
7072 be the current value of your @code{$PATH} environment variable, since
7073 the @code{value} function avoided the expansion.
7075 The @code{value} function is most often used in conjunction with the
7076 @code{eval} function (@pxref{Eval Function}).
7078 @node Eval Function, Origin Function, Value Function, Functions
7079 @comment node-name, next, previous, up
7080 @section The @code{eval} Function
7082 @cindex evaluating makefile syntax
7083 @cindex makefile syntax, evaluating
7085 The @code{eval} function is very special: it allows you to define new
7086 makefile constructs that are not constant; which are the result of
7087 evaluating other variables and functions. The argument to the
7088 @code{eval} function is expanded, then the results of that expansion
7089 are parsed as makefile syntax. The expanded results can define new
7090 @code{make} variables, targets, implicit or explicit rules, etc.
7092 The result of the @code{eval} function is always the empty string;
7093 thus, it can be placed virtually anywhere in a makefile without
7094 causing syntax errors.
7096 It's important to realize that the @code{eval} argument is expanded
7097 @emph{twice}; first by the @code{eval} function, then the results of
7098 that expansion are expanded again when they are parsed as makefile
7099 syntax. This means you may need to provide extra levels of escaping
7100 for ``$'' characters when using @code{eval}. The @code{value}
7101 function (@pxref{Value Function}) can sometimes be useful in these
7102 situations, to circumvent unwanted expansions.
7104 Here is an example of how @code{eval} can be used; this example
7105 combines a number of concepts and other functions. Although it might
7106 seem overly complex to use @code{eval} in this example, rather than
7107 just writing out the rules, consider two things: first, the template
7108 definition (in @code{PROGRAM_template}) could need to be much more
7109 complex than it is here; and second, you might put the complex,
7110 ``generic'' part of this example into another makefile, then include
7111 it in all the individual makefiles. Now your individual makefiles are
7112 quite straightforward.
7116 PROGRAMS = server client
7118 server_OBJS = server.o server_priv.o server_access.o
7119 server_LIBS = priv protocol
7121 client_OBJS = client.o client_api.o client_mem.o
7122 client_LIBS = protocol
7124 # Everything after this is generic
7129 define PROGRAM_template
7130 $(1): $$($(1)_OBJS) $$($(1)_LIBS:%=-l%)
7131 ALL_OBJS += $$($(1)_OBJS)
7134 $(foreach prog,$(PROGRAMS),$(eval $(call PROGRAM_template,$(prog))))
7137 $(LINK.o) $^ $(LDLIBS) -o $@@
7140 rm -f $(ALL_OBJS) $(PROGRAMS)
7144 @node Origin Function, Flavor Function, Eval Function, Functions
7145 @section The @code{origin} Function
7147 @cindex variables, origin of
7148 @cindex origin of variable
7150 The @code{origin} function is unlike most other functions in that it does
7151 not operate on the values of variables; it tells you something @emph{about}
7152 a variable. Specifically, it tells you where it came from.
7154 The syntax of the @code{origin} function is:
7157 $(origin @var{variable})
7160 Note that @var{variable} is the @emph{name} of a variable to inquire about;
7161 not a @emph{reference} to that variable. Therefore you would not normally
7162 use a @samp{$} or parentheses when writing it. (You can, however, use a
7163 variable reference in the name if you want the name not to be a constant.)
7165 The result of this function is a string telling you how the variable
7166 @var{variable} was defined:
7171 if @var{variable} was never defined.
7175 if @var{variable} has a default definition, as is usual with @code{CC}
7176 and so on. @xref{Implicit Variables, ,Variables Used by Implicit Rules}.
7177 Note that if you have redefined a default variable, the @code{origin}
7178 function will return the origin of the later definition.
7182 if @var{variable} was defined as an environment variable and the
7183 @samp{-e} option is @emph{not} turned on (@pxref{Options Summary, ,Summary of Options}).
7185 @item environment override
7187 if @var{variable} was defined as an environment variable and the
7188 @w{@samp{-e}} option @emph{is} turned on (@pxref{Options Summary,
7189 ,Summary of Options}).@refill
7193 if @var{variable} was defined in a makefile.
7197 if @var{variable} was defined on the command line.
7201 if @var{variable} was defined with an @code{override} directive in a
7202 makefile (@pxref{Override Directive, ,The @code{override} Directive}).
7206 if @var{variable} is an automatic variable defined for the
7207 execution of the commands for each rule
7208 (@pxref{Automatic Variables}).
7211 This information is primarily useful (other than for your curiosity) to
7212 determine if you want to believe the value of a variable. For example,
7213 suppose you have a makefile @file{foo} that includes another makefile
7214 @file{bar}. You want a variable @code{bletch} to be defined in @file{bar}
7215 if you run the command @w{@samp{make -f bar}}, even if the environment contains
7216 a definition of @code{bletch}. However, if @file{foo} defined
7217 @code{bletch} before including @file{bar}, you do not want to override that
7218 definition. This could be done by using an @code{override} directive in
7219 @file{foo}, giving that definition precedence over the later definition in
7220 @file{bar}; unfortunately, the @code{override} directive would also
7221 override any command line definitions. So, @file{bar} could
7227 ifeq "$(origin bletch)" "environment"
7228 bletch = barf, gag, etc.
7235 If @code{bletch} has been defined from the environment, this will redefine
7238 If you want to override a previous definition of @code{bletch} if it came
7239 from the environment, even under @samp{-e}, you could instead write:
7243 ifneq "$(findstring environment,$(origin bletch))" ""
7244 bletch = barf, gag, etc.
7249 Here the redefinition takes place if @samp{$(origin bletch)} returns either
7250 @samp{environment} or @samp{environment override}.
7251 @xref{Text Functions, , Functions for String Substitution and Analysis}.
7253 @node Flavor Function, Shell Function, Origin Function, Functions
7254 @section The @code{flavor} Function
7256 @cindex variables, flavor of
7257 @cindex flavor of variable
7259 The @code{flavor} function is unlike most other functions (and like
7260 @code{origin} function) in that it does not operate on the values of
7261 variables; it tells you something @emph{about} a variable.
7262 Specifically, it tells you the flavor of a variable (@pxref{Flavors,
7263 ,The Two Flavors of Variables}).
7265 The syntax of the @code{flavor} function is:
7268 $(flavor @var{variable})
7271 Note that @var{variable} is the @emph{name} of a variable to inquire about;
7272 not a @emph{reference} to that variable. Therefore you would not normally
7273 use a @samp{$} or parentheses when writing it. (You can, however, use a
7274 variable reference in the name if you want the name not to be a constant.)
7276 The result of this function is a string that identifies the flavor of the
7277 variable @var{variable}:
7282 if @var{variable} was never defined.
7286 if @var{variable} is a recursively expanded variable.
7290 if @var{variable} is a simply expanded variable.
7295 @node Shell Function, Make Control Functions, Flavor Function, Functions
7296 @section The @code{shell} Function
7298 @cindex commands, expansion
7300 @cindex shell command, function for
7302 The @code{shell} function is unlike any other function other than the
7303 @code{wildcard} function
7304 (@pxref{Wildcard Function, ,The Function @code{wildcard}}) in that it
7305 communicates with the world outside of @code{make}.
7307 The @code{shell} function performs the same function that backquotes
7308 (@samp{`}) perform in most shells: it does @dfn{command expansion}.
7309 This means that it takes as an argument a shell command and evaluates
7310 to the output of the command. The only processing @code{make} does on
7311 the result is to convert each newline (or carriage-return / newline
7312 pair) to a single space. If there is a trailing (carriage-return
7313 and) newline it will simply be removed.@refill
7315 The commands run by calls to the @code{shell} function are run when the
7316 function calls are expanded (@pxref{Reading Makefiles, , How
7317 @code{make} Reads a Makefile}). Because this function involves
7318 spawning a new shell, you should carefully consider the performance
7319 implications of using the @code{shell} function within recursively
7320 expanded variables vs.@: simply expanded variables (@pxref{Flavors, ,The
7321 Two Flavors of Variables}).
7323 Here are some examples of the use of the @code{shell} function:
7326 contents := $(shell cat foo)
7330 sets @code{contents} to the contents of the file @file{foo}, with a space
7331 (rather than a newline) separating each line.
7334 files := $(shell echo *.c)
7338 sets @code{files} to the expansion of @samp{*.c}. Unless @code{make} is
7339 using a very strange shell, this has the same result as
7340 @w{@samp{$(wildcard *.c)}} (as long as at least one @samp{.c} file
7343 @node Make Control Functions, , Shell Function, Functions
7344 @section Functions That Control Make
7345 @cindex functions, for controlling make
7346 @cindex controlling make
7348 These functions control the way make runs. Generally, they are used to
7349 provide information to the user of the makefile or to cause make to stop
7350 if some sort of environmental error is detected.
7353 @item $(error @var{text}@dots{})
7355 @cindex error, stopping on
7356 @cindex stopping make
7357 Generates a fatal error where the message is @var{text}. Note that the
7358 error is generated whenever this function is evaluated. So, if you put
7359 it inside a command script or on the right side of a recursive variable
7360 assignment, it won't be evaluated until later. The @var{text} will be
7361 expanded before the error is generated.
7367 $(error error is $(ERROR1))
7372 will generate a fatal error during the read of the makefile if the
7373 @code{make} variable @code{ERROR1} is defined. Or,
7376 ERR = $(error found an error!)
7383 will generate a fatal error while @code{make} is running, if the
7384 @code{err} target is invoked.
7386 @item $(warning @var{text}@dots{})
7388 @cindex warnings, printing
7389 @cindex printing user warnings
7390 This function works similarly to the @code{error} function, above,
7391 except that @code{make} doesn't exit. Instead, @var{text} is expanded
7392 and the resulting message is displayed, but processing of the makefile
7395 The result of the expansion of this function is the empty string.
7397 @item $(info @var{text}@dots{})
7399 @cindex printing messages
7400 This function does nothing more than print its (expanded) argument(s)
7401 to standard output. No makefile name or line number is added. The
7402 result of the expansion of this function is the empty string.
7405 @node Running, Implicit Rules, Functions, Top
7406 @chapter How to Run @code{make}
7408 A makefile that says how to recompile a program can be used in more
7409 than one way. The simplest use is to recompile every file that is out
7410 of date. Usually, makefiles are written so that if you run
7411 @code{make} with no arguments, it does just that.
7413 But you might want to update only some of the files; you might want to use
7414 a different compiler or different compiler options; you might want just to
7415 find out which files are out of date without changing them.
7417 By giving arguments when you run @code{make}, you can do any of these
7418 things and many others.
7420 @cindex exit status of make
7421 The exit status of @code{make} is always one of three values:
7424 The exit status is zero if @code{make} is successful.
7426 The exit status is two if @code{make} encounters any errors.
7427 It will print messages describing the particular errors.
7429 The exit status is one if you use the @samp{-q} flag and @code{make}
7430 determines that some target is not already up to date.
7431 @xref{Instead of Execution, ,Instead of Executing the Commands}.
7435 * Makefile Arguments:: How to specify which makefile to use.
7436 * Goals:: How to use goal arguments to specify which
7437 parts of the makefile to use.
7438 * Instead of Execution:: How to use mode flags to specify what
7439 kind of thing to do with the commands
7440 in the makefile other than simply
7442 * Avoiding Compilation:: How to avoid recompiling certain files.
7443 * Overriding:: How to override a variable to specify
7444 an alternate compiler and other things.
7445 * Testing:: How to proceed past some errors, to
7447 * Options Summary:: Summary of Options
7450 @node Makefile Arguments, Goals, Running, Running
7451 @section Arguments to Specify the Makefile
7452 @cindex @code{--file}
7453 @cindex @code{--makefile}
7456 The way to specify the name of the makefile is with the @samp{-f} or
7457 @samp{--file} option (@samp{--makefile} also works). For example,
7458 @samp{-f altmake} says to use the file @file{altmake} as the makefile.
7460 If you use the @samp{-f} flag several times and follow each @samp{-f}
7461 with an argument, all the specified files are used jointly as
7464 If you do not use the @samp{-f} or @samp{--file} flag, the default is
7465 to try @file{GNUmakefile}, @file{makefile}, and @file{Makefile}, in
7466 that order, and use the first of these three which exists or can be made
7467 (@pxref{Makefiles, ,Writing Makefiles}).@refill
7469 @node Goals, Instead of Execution, Makefile Arguments, Running
7470 @section Arguments to Specify the Goals
7471 @cindex goal, how to specify
7473 The @dfn{goals} are the targets that @code{make} should strive ultimately
7474 to update. Other targets are updated as well if they appear as
7475 prerequisites of goals, or prerequisites of prerequisites of goals, etc.
7477 By default, the goal is the first target in the makefile (not counting
7478 targets that start with a period). Therefore, makefiles are usually
7479 written so that the first target is for compiling the entire program or
7480 programs they describe. If the first rule in the makefile has several
7481 targets, only the first target in the rule becomes the default goal, not
7482 the whole list. You can manage the selection of the default goal from
7483 within your makefile using the @code{.DEFAULT_GOAL} variable
7484 (@pxref{Special Variables, , Other Special Variables}).
7486 You can also specify a different goal or goals with command-line
7487 arguments to @code{make}. Use the name of the goal as an argument.
7488 If you specify several goals, @code{make} processes each of them in
7489 turn, in the order you name them.
7491 Any target in the makefile may be specified as a goal (unless it
7492 starts with @samp{-} or contains an @samp{=}, in which case it will be
7493 parsed as a switch or variable definition, respectively). Even
7494 targets not in the makefile may be specified, if @code{make} can find
7495 implicit rules that say how to make them.
7497 @vindex MAKECMDGOALS
7498 @code{Make} will set the special variable @code{MAKECMDGOALS} to the
7499 list of goals you specified on the command line. If no goals were given
7500 on the command line, this variable is empty. Note that this variable
7501 should be used only in special circumstances.
7503 An example of appropriate use is to avoid including @file{.d} files
7504 during @code{clean} rules (@pxref{Automatic Prerequisites}), so
7505 @code{make} won't create them only to immediately remove them
7510 sources = foo.c bar.c
7512 ifneq ($(MAKECMDGOALS),clean)
7513 include $(sources:.c=.d)
7518 One use of specifying a goal is if you want to compile only a part of
7519 the program, or only one of several programs. Specify as a goal each
7520 file that you wish to remake. For example, consider a directory containing
7521 several programs, with a makefile that starts like this:
7525 all: size nm ld ar as
7528 If you are working on the program @code{size}, you might want to say
7529 @w{@samp{make size}} so that only the files of that program are recompiled.
7531 Another use of specifying a goal is to make files that are not normally
7532 made. For example, there may be a file of debugging output, or a
7533 version of the program that is compiled specially for testing, which has
7534 a rule in the makefile but is not a prerequisite of the default goal.
7536 Another use of specifying a goal is to run the commands associated with
7537 a phony target (@pxref{Phony Targets}) or empty target (@pxref{Empty
7538 Targets, ,Empty Target Files to Record Events}). Many makefiles contain
7539 a phony target named @file{clean} which deletes everything except source
7540 files. Naturally, this is done only if you request it explicitly with
7541 @w{@samp{make clean}}. Following is a list of typical phony and empty
7542 target names. @xref{Standard Targets}, for a detailed list of all the
7543 standard target names which GNU software packages use.
7547 @cindex @code{all} @r{(standard target)}
7548 Make all the top-level targets the makefile knows about.
7551 @cindex @code{clean} @r{(standard target)}
7552 Delete all files that are normally created by running @code{make}.
7555 @cindex @code{mostlyclean} @r{(standard target)}
7556 Like @samp{clean}, but may refrain from deleting a few files that people
7557 normally don't want to recompile. For example, the @samp{mostlyclean}
7558 target for GCC does not delete @file{libgcc.a}, because recompiling it
7559 is rarely necessary and takes a lot of time.
7562 @cindex @code{distclean} @r{(standard target)}
7564 @cindex @code{realclean} @r{(standard target)}
7566 @cindex @code{clobber} @r{(standard target)}
7567 Any of these targets might be defined to delete @emph{more} files than
7568 @samp{clean} does. For example, this would delete configuration files
7569 or links that you would normally create as preparation for compilation,
7570 even if the makefile itself cannot create these files.
7573 @cindex @code{install} @r{(standard target)}
7574 Copy the executable file into a directory that users typically search
7575 for commands; copy any auxiliary files that the executable uses into
7576 the directories where it will look for them.
7579 @cindex @code{print} @r{(standard target)}
7580 Print listings of the source files that have changed.
7583 @cindex @code{tar} @r{(standard target)}
7584 Create a tar file of the source files.
7587 @cindex @code{shar} @r{(standard target)}
7588 Create a shell archive (shar file) of the source files.
7591 @cindex @code{dist} @r{(standard target)}
7592 Create a distribution file of the source files. This might
7593 be a tar file, or a shar file, or a compressed version of one of the
7594 above, or even more than one of the above.
7597 @cindex @code{TAGS} @r{(standard target)}
7598 Update a tags table for this program.
7601 @cindex @code{check} @r{(standard target)}
7603 @cindex @code{test} @r{(standard target)}
7604 Perform self tests on the program this makefile builds.
7607 @node Instead of Execution, Avoiding Compilation, Goals, Running
7608 @section Instead of Executing the Commands
7609 @cindex execution, instead of
7610 @cindex commands, instead of executing
7612 The makefile tells @code{make} how to tell whether a target is up to date,
7613 and how to update each target. But updating the targets is not always
7614 what you want. Certain options specify other activities for @code{make}.
7616 @comment Extra blank lines make it print better.
7622 @cindex @code{--just-print}
7623 @cindex @code{--dry-run}
7624 @cindex @code{--recon}
7627 ``No-op''. The activity is to print what commands would be used to make
7628 the targets up to date, but not actually execute them.
7632 @cindex @code{--touch}
7633 @cindex touching files
7634 @cindex target, touching
7637 ``Touch''. The activity is to mark the targets as up to date without
7638 actually changing them. In other words, @code{make} pretends to compile
7639 the targets but does not really change their contents.
7643 @cindex @code{--question}
7645 @cindex question mode
7647 ``Question''. The activity is to find out silently whether the targets
7648 are up to date already; but execute no commands in either case. In other
7649 words, neither compilation nor output will occur.
7652 @itemx --what-if=@var{file}
7653 @itemx --assume-new=@var{file}
7654 @itemx --new-file=@var{file}
7655 @cindex @code{--what-if}
7657 @cindex @code{--assume-new}
7658 @cindex @code{--new-file}
7660 @cindex files, assuming new
7662 ``What if''. Each @samp{-W} flag is followed by a file name. The given
7663 files' modification times are recorded by @code{make} as being the present
7664 time, although the actual modification times remain the same.
7665 You can use the @samp{-W} flag in conjunction with the @samp{-n} flag
7666 to see what would happen if you were to modify specific files.@refill
7669 With the @samp{-n} flag, @code{make} prints the commands that it would
7670 normally execute but does not execute them.
7672 With the @samp{-t} flag, @code{make} ignores the commands in the rules
7673 and uses (in effect) the command @code{touch} for each target that needs to
7674 be remade. The @code{touch} command is also printed, unless @samp{-s} or
7675 @code{.SILENT} is used. For speed, @code{make} does not actually invoke
7676 the program @code{touch}. It does the work directly.
7678 With the @samp{-q} flag, @code{make} prints nothing and executes no
7679 commands, but the exit status code it returns is zero if and only if the
7680 targets to be considered are already up to date. If the exit status is
7681 one, then some updating needs to be done. If @code{make} encounters an
7682 error, the exit status is two, so you can distinguish an error from a
7683 target that is not up to date.
7685 It is an error to use more than one of these three flags in the same
7686 invocation of @code{make}.
7688 @cindex +, and command execution
7689 The @samp{-n}, @samp{-t}, and @samp{-q} options do not affect command
7690 lines that begin with @samp{+} characters or contain the strings
7691 @samp{$(MAKE)} or @samp{$@{MAKE@}}. Note that only the line containing
7692 the @samp{+} character or the strings @samp{$(MAKE)} or @samp{$@{MAKE@}}
7693 is run regardless of these options. Other lines in the same rule are
7694 not run unless they too begin with @samp{+} or contain @samp{$(MAKE)} or
7695 @samp{$@{MAKE@}} (@xref{MAKE Variable, ,How the @code{MAKE} Variable Works}.)
7697 The @samp{-W} flag provides two features:
7701 If you also use the @samp{-n} or @samp{-q} flag, you can see what
7702 @code{make} would do if you were to modify some files.
7705 Without the @samp{-n} or @samp{-q} flag, when @code{make} is actually
7706 executing commands, the @samp{-W} flag can direct @code{make} to act
7707 as if some files had been modified, without actually modifying the
7711 Note that the options @samp{-p} and @samp{-v} allow you to obtain other
7712 information about @code{make} or about the makefiles in use
7713 (@pxref{Options Summary, ,Summary of Options}).@refill
7715 @node Avoiding Compilation, Overriding, Instead of Execution, Running
7716 @section Avoiding Recompilation of Some Files
7718 @cindex @code{--old-file}
7719 @cindex @code{--assume-old}
7720 @cindex files, assuming old
7721 @cindex files, avoiding recompilation of
7722 @cindex recompilation, avoiding
7724 Sometimes you may have changed a source file but you do not want to
7725 recompile all the files that depend on it. For example, suppose you add
7726 a macro or a declaration to a header file that many other files depend
7727 on. Being conservative, @code{make} assumes that any change in the
7728 header file requires recompilation of all dependent files, but you know
7729 that they do not need to be recompiled and you would rather not waste
7730 the time waiting for them to compile.
7732 If you anticipate the problem before changing the header file, you can
7733 use the @samp{-t} flag. This flag tells @code{make} not to run the
7734 commands in the rules, but rather to mark the target up to date by
7735 changing its last-modification date. You would follow this procedure:
7739 Use the command @samp{make} to recompile the source files that really
7740 need recompilation, ensuring that the object files are up-to-date
7744 Make the changes in the header files.
7747 Use the command @samp{make -t} to mark all the object files as
7748 up to date. The next time you run @code{make}, the changes in the
7749 header files will not cause any recompilation.
7752 If you have already changed the header file at a time when some files
7753 do need recompilation, it is too late to do this. Instead, you can
7754 use the @w{@samp{-o @var{file}}} flag, which marks a specified file as
7755 ``old'' (@pxref{Options Summary, ,Summary of Options}). This means
7756 that the file itself will not be remade, and nothing else will be
7757 remade on its account. Follow this procedure:
7761 Recompile the source files that need compilation for reasons independent
7762 of the particular header file, with @samp{make -o @var{headerfile}}.
7763 If several header files are involved, use a separate @samp{-o} option
7764 for each header file.
7767 Touch all the object files with @samp{make -t}.
7770 @node Overriding, Testing, Avoiding Compilation, Running
7771 @section Overriding Variables
7772 @cindex overriding variables with arguments
7773 @cindex variables, overriding with arguments
7774 @cindex command line variables
7775 @cindex variables, command line
7777 An argument that contains @samp{=} specifies the value of a variable:
7778 @samp{@var{v}=@var{x}} sets the value of the variable @var{v} to @var{x}.
7779 If you specify a value in this way, all ordinary assignments of the same
7780 variable in the makefile are ignored; we say they have been
7781 @dfn{overridden} by the command line argument.
7783 The most common way to use this facility is to pass extra flags to
7784 compilers. For example, in a properly written makefile, the variable
7785 @code{CFLAGS} is included in each command that runs the C compiler, so a
7786 file @file{foo.c} would be compiled something like this:
7789 cc -c $(CFLAGS) foo.c
7792 Thus, whatever value you set for @code{CFLAGS} affects each compilation
7793 that occurs. The makefile probably specifies the usual value for
7794 @code{CFLAGS}, like this:
7800 Each time you run @code{make}, you can override this value if you
7801 wish. For example, if you say @samp{make CFLAGS='-g -O'}, each C
7802 compilation will be done with @samp{cc -c -g -O}. (This also
7803 illustrates how you can use quoting in the shell to enclose spaces and
7804 other special characters in the value of a variable when you override
7807 The variable @code{CFLAGS} is only one of many standard variables that
7808 exist just so that you can change them this way. @xref{Implicit
7809 Variables, , Variables Used by Implicit Rules}, for a complete list.
7811 You can also program the makefile to look at additional variables of your
7812 own, giving the user the ability to control other aspects of how the
7813 makefile works by changing the variables.
7815 When you override a variable with a command argument, you can define either
7816 a recursively-expanded variable or a simply-expanded variable. The
7817 examples shown above make a recursively-expanded variable; to make a
7818 simply-expanded variable, write @samp{:=} instead of @samp{=}. But, unless
7819 you want to include a variable reference or function call in the
7820 @emph{value} that you specify, it makes no difference which kind of
7821 variable you create.
7823 There is one way that the makefile can change a variable that you have
7824 overridden. This is to use the @code{override} directive, which is a line
7825 that looks like this: @samp{override @var{variable} = @var{value}}
7826 (@pxref{Override Directive, ,The @code{override} Directive}).
7828 @node Testing, Options Summary, Overriding, Running
7829 @section Testing the Compilation of a Program
7830 @cindex testing compilation
7831 @cindex compilation, testing
7833 Normally, when an error happens in executing a shell command, @code{make}
7834 gives up immediately, returning a nonzero status. No further commands are
7835 executed for any target. The error implies that the goal cannot be
7836 correctly remade, and @code{make} reports this as soon as it knows.
7838 When you are compiling a program that you have just changed, this is not
7839 what you want. Instead, you would rather that @code{make} try compiling
7840 every file that can be tried, to show you as many compilation errors
7844 @cindex @code{--keep-going}
7845 On these occasions, you should use the @samp{-k} or
7846 @samp{--keep-going} flag. This tells @code{make} to continue to
7847 consider the other prerequisites of the pending targets, remaking them
7848 if necessary, before it gives up and returns nonzero status. For
7849 example, after an error in compiling one object file, @samp{make -k}
7850 will continue compiling other object files even though it already
7851 knows that linking them will be impossible. In addition to continuing
7852 after failed shell commands, @samp{make -k} will continue as much as
7853 possible after discovering that it does not know how to make a target
7854 or prerequisite file. This will always cause an error message, but
7855 without @samp{-k}, it is a fatal error (@pxref{Options Summary,
7856 ,Summary of Options}).@refill
7858 The usual behavior of @code{make} assumes that your purpose is to get the
7859 goals up to date; once @code{make} learns that this is impossible, it might
7860 as well report the failure immediately. The @samp{-k} flag says that the
7861 real purpose is to test as much as possible of the changes made in the
7862 program, perhaps to find several independent problems so that you can
7863 correct them all before the next attempt to compile. This is why Emacs'
7864 @kbd{M-x compile} command passes the @samp{-k} flag by default.
7866 @node Options Summary, , Testing, Running
7867 @section Summary of Options
7872 Here is a table of all the options @code{make} understands:
7879 These options are ignored for compatibility with other versions of @code{make}.
7883 @itemx --always-make
7884 @cindex @code{--always-make}
7885 Consider all targets out-of-date. GNU @code{make} proceeds to
7886 consider targets and their prerequisites using the normal algorithms;
7887 however, all targets so considered are always remade regardless of the
7888 status of their prerequisites. To avoid infinite recursion, if
7889 @code{MAKE_RESTARTS} (@pxref{Special Variables, , Other Special
7890 Variables}) is set to a number greater than 0 this option is disabled
7891 when considering whether to remake makefiles (@pxref{Remaking
7892 Makefiles, , How Makefiles Are Remade}).
7896 @itemx --directory=@var{dir}
7897 @cindex @code{--directory}
7898 Change to directory @var{dir} before reading the makefiles. If multiple
7899 @samp{-C} options are specified, each is interpreted relative to the
7900 previous one: @samp{-C / -C etc} is equivalent to @samp{-C /etc}.
7901 This is typically used with recursive invocations of @code{make}
7902 (@pxref{Recursion, ,Recursive Use of @code{make}}).
7906 @c Extra blank line here makes the table look better.
7908 Print debugging information in addition to normal processing. The
7909 debugging information says which files are being considered for
7910 remaking, which file-times are being compared and with what results,
7911 which files actually need to be remade, which implicit rules are
7912 considered and which are applied---everything interesting about how
7913 @code{make} decides what to do. The @code{-d} option is equivalent to
7914 @samp{--debug=a} (see below).
7916 @item --debug[=@var{options}]
7917 @cindex @code{--debug}
7918 @c Extra blank line here makes the table look better.
7920 Print debugging information in addition to normal processing. Various
7921 levels and types of output can be chosen. With no arguments, print the
7922 ``basic'' level of debugging. Possible arguments are below; only the
7923 first character is considered, and values must be comma- or
7928 All types of debugging output are enabled. This is equivalent to using
7932 Basic debugging prints each target that was found to be out-of-date, and
7933 whether the build was successful or not.
7935 @item v (@i{verbose})
7936 A level above @samp{basic}; includes messages about which makefiles were
7937 parsed, prerequisites that did not need to be rebuilt, etc. This option
7938 also enables @samp{basic} messages.
7940 @item i (@i{implicit})
7941 Prints messages describing the implicit rule searches for each target.
7942 This option also enables @samp{basic} messages.
7945 Prints messages giving details on the invocation of specific subcommands.
7947 @item m (@i{makefile})
7948 By default, the above messages are not enabled while trying to remake
7949 the makefiles. This option enables messages while rebuilding makefiles,
7950 too. Note that the @samp{all} option does enable this option. This
7951 option also enables @samp{basic} messages.
7956 @itemx --environment-overrides
7957 @cindex @code{--environment-overrides}
7958 Give variables taken from the environment precedence
7959 over variables from makefiles.
7960 @xref{Environment, ,Variables from the Environment}.
7964 @itemx --file=@var{file}
7965 @cindex @code{--file}
7966 @itemx --makefile=@var{file}
7967 @cindex @code{--makefile}
7968 Read the file named @var{file} as a makefile.
7969 @xref{Makefiles, ,Writing Makefiles}.
7974 @cindex @code{--help}
7975 @c Extra blank line here makes the table look better.
7977 Remind you of the options that @code{make} understands and then exit.
7981 @itemx --ignore-errors
7982 @cindex @code{--ignore-errors}
7983 Ignore all errors in commands executed to remake files.
7984 @xref{Errors, ,Errors in Commands}.
7988 @itemx --include-dir=@var{dir}
7989 @cindex @code{--include-dir}
7990 Specifies a directory @var{dir} to search for included makefiles.
7991 @xref{Include, ,Including Other Makefiles}. If several @samp{-I}
7992 options are used to specify several directories, the directories are
7993 searched in the order specified.
7995 @item -j [@var{jobs}]
7997 @itemx --jobs[=@var{jobs}]
7998 @cindex @code{--jobs}
7999 Specifies the number of jobs (commands) to run simultaneously. With no
8000 argument, @code{make} runs as many jobs simultaneously as possible. If
8001 there is more than one @samp{-j} option, the last one is effective.
8002 @xref{Parallel, ,Parallel Execution},
8003 for more information on how commands are run.
8004 Note that this option is ignored on MS-DOS.
8009 @cindex @code{--keep-going}
8010 Continue as much as possible after an error. While the target that
8011 failed, and those that depend on it, cannot be remade, the other
8012 prerequisites of these targets can be processed all the same.
8013 @xref{Testing, ,Testing the Compilation of a Program}.
8015 @item -l [@var{load}]
8017 @itemx --load-average[=@var{load}]
8018 @cindex @code{--load-average}
8019 @itemx --max-load[=@var{load}]
8020 @cindex @code{--max-load}
8021 Specifies that no new jobs (commands) should be started if there are
8022 other jobs running and the load average is at least @var{load} (a
8023 floating-point number). With no argument, removes a previous load
8024 limit. @xref{Parallel, ,Parallel Execution}.
8028 @itemx --check-symlink-times
8029 @cindex @code{--check-symlink-times}
8030 On systems that support symbolic links, this option causes @code{make}
8031 to consider the timestamps on any symbolic links in addition to the
8032 timestamp on the file referenced by those links. When this option is
8033 provided, the most recent timestamp among the file and the symbolic
8034 links is taken as the modification time for this target file.
8039 @cindex @code{--just-print}
8041 @cindex @code{--dry-run}
8043 @cindex @code{--recon}
8044 @c Extra blank line here makes the table look better.
8046 Print the commands that would be executed, but do not execute them.
8047 @xref{Instead of Execution, ,Instead of Executing the Commands}.
8051 @itemx --old-file=@var{file}
8052 @cindex @code{--old-file}
8053 @itemx --assume-old=@var{file}
8054 @cindex @code{--assume-old}
8055 Do not remake the file @var{file} even if it is older than its
8056 prerequisites, and do not remake anything on account of changes in
8057 @var{file}. Essentially the file is treated as very old and its rules
8058 are ignored. @xref{Avoiding Compilation, ,Avoiding Recompilation of
8063 @itemx --print-data-base
8064 @cindex @code{--print-data-base}
8065 @cindex data base of @code{make} rules
8066 @cindex predefined rules and variables, printing
8067 Print the data base (rules and variable values) that results from
8068 reading the makefiles; then execute as usual or as otherwise specified.
8069 This also prints the version information given by the @samp{-v} switch
8070 (see below). To print the data base without trying to remake any files,
8071 use @w{@samp{make -qp}}. To print the data base of predefined rules and
8072 variables, use @w{@samp{make -p -f /dev/null}}. The data base output
8073 contains filename and linenumber information for command and variable
8074 definitions, so it can be a useful debugging tool in complex environments.
8079 @cindex @code{--question}
8080 ``Question mode''. Do not run any commands, or print anything; just
8081 return an exit status that is zero if the specified targets are already
8082 up to date, one if any remaking is required, or two if an error is
8083 encountered. @xref{Instead of Execution, ,Instead of Executing the
8088 @itemx --no-builtin-rules
8089 @cindex @code{--no-builtin-rules}
8090 Eliminate use of the built-in implicit rules (@pxref{Implicit Rules,
8091 ,Using Implicit Rules}). You can still define your own by writing
8092 pattern rules (@pxref{Pattern Rules, ,Defining and Redefining Pattern
8093 Rules}). The @samp{-r} option also clears out the default list of
8094 suffixes for suffix rules (@pxref{Suffix Rules, ,Old-Fashioned Suffix
8095 Rules}). But you can still define your own suffixes with a rule for
8096 @code{.SUFFIXES}, and then define your own suffix rules. Note that only
8097 @emph{rules} are affected by the @code{-r} option; default variables
8098 remain in effect (@pxref{Implicit Variables, ,Variables Used by Implicit
8099 Rules}); see the @samp{-R} option below.
8103 @itemx --no-builtin-variables
8104 @cindex @code{--no-builtin-variables}
8105 Eliminate use of the built-in rule-specific variables (@pxref{Implicit
8106 Variables, ,Variables Used by Implicit Rules}). You can still define
8107 your own, of course. The @samp{-R} option also automatically enables
8108 the @samp{-r} option (see above), since it doesn't make sense to have
8109 implicit rules without any definitions for the variables that they use.
8114 @cindex @code{--silent}
8116 @cindex @code{--quiet}
8117 @c Extra blank line here makes the table look better.
8119 Silent operation; do not print the commands as they are executed.
8120 @xref{Echoing, ,Command Echoing}.
8124 @itemx --no-keep-going
8125 @cindex @code{--no-keep-going}
8127 @cindex @code{--stop}
8128 @c Extra blank line here makes the table look better.
8130 Cancel the effect of the @samp{-k} option. This is never necessary
8131 except in a recursive @code{make} where @samp{-k} might be inherited
8132 from the top-level @code{make} via @code{MAKEFLAGS}
8133 (@pxref{Recursion, ,Recursive Use of @code{make}})
8134 or if you set @samp{-k} in @code{MAKEFLAGS} in your environment.@refill
8139 @cindex @code{--touch}
8140 @c Extra blank line here makes the table look better.
8142 Touch files (mark them up to date without really changing them)
8143 instead of running their commands. This is used to pretend that the
8144 commands were done, in order to fool future invocations of
8145 @code{make}. @xref{Instead of Execution, ,Instead of Executing the Commands}.
8150 @cindex @code{--version}
8151 Print the version of the @code{make} program plus a copyright, a list
8152 of authors, and a notice that there is no warranty; then exit.
8156 @itemx --print-directory
8157 @cindex @code{--print-directory}
8158 Print a message containing the working directory both before and after
8159 executing the makefile. This may be useful for tracking down errors
8160 from complicated nests of recursive @code{make} commands.
8161 @xref{Recursion, ,Recursive Use of @code{make}}. (In practice, you
8162 rarely need to specify this option since @samp{make} does it for you;
8163 see @ref{-w Option, ,The @samp{--print-directory} Option}.)
8165 @itemx --no-print-directory
8166 @cindex @code{--no-print-directory}
8167 Disable printing of the working directory under @code{-w}.
8168 This option is useful when @code{-w} is turned on automatically,
8169 but you do not want to see the extra messages.
8170 @xref{-w Option, ,The @samp{--print-directory} Option}.
8174 @itemx --what-if=@var{file}
8175 @cindex @code{--what-if}
8176 @itemx --new-file=@var{file}
8177 @cindex @code{--new-file}
8178 @itemx --assume-new=@var{file}
8179 @cindex @code{--assume-new}
8180 Pretend that the target @var{file} has just been modified. When used
8181 with the @samp{-n} flag, this shows you what would happen if you were
8182 to modify that file. Without @samp{-n}, it is almost the same as
8183 running a @code{touch} command on the given file before running
8184 @code{make}, except that the modification time is changed only in the
8185 imagination of @code{make}.
8186 @xref{Instead of Execution, ,Instead of Executing the Commands}.
8188 @item --warn-undefined-variables
8189 @cindex @code{--warn-undefined-variables}
8190 @cindex variables, warning for undefined
8191 @cindex undefined variables, warning message
8192 Issue a warning message whenever @code{make} sees a reference to an
8193 undefined variable. This can be helpful when you are trying to debug
8194 makefiles which use variables in complex ways.
8197 @node Implicit Rules, Archives, Running, Top
8198 @chapter Using Implicit Rules
8199 @cindex implicit rule
8200 @cindex rule, implicit
8202 Certain standard ways of remaking target files are used very often. For
8203 example, one customary way to make an object file is from a C source file
8204 using the C compiler, @code{cc}.
8206 @dfn{Implicit rules} tell @code{make} how to use customary techniques so
8207 that you do not have to specify them in detail when you want to use
8208 them. For example, there is an implicit rule for C compilation. File
8209 names determine which implicit rules are run. For example, C
8210 compilation typically takes a @file{.c} file and makes a @file{.o} file.
8211 So @code{make} applies the implicit rule for C compilation when it sees
8212 this combination of file name endings.@refill
8214 A chain of implicit rules can apply in sequence; for example, @code{make}
8215 will remake a @file{.o} file from a @file{.y} file by way of a @file{.c} file.
8217 @xref{Chained Rules, ,Chains of Implicit Rules}.
8220 The built-in implicit rules use several variables in their commands so
8221 that, by changing the values of the variables, you can change the way the
8222 implicit rule works. For example, the variable @code{CFLAGS} controls the
8223 flags given to the C compiler by the implicit rule for C compilation.
8225 @xref{Implicit Variables, ,Variables Used by Implicit Rules}.
8228 You can define your own implicit rules by writing @dfn{pattern rules}.
8230 @xref{Pattern Rules, ,Defining and Redefining Pattern Rules}.
8233 @dfn{Suffix rules} are a more limited way to define implicit rules.
8234 Pattern rules are more general and clearer, but suffix rules are
8235 retained for compatibility.
8237 @xref{Suffix Rules, ,Old-Fashioned Suffix Rules}.
8241 * Using Implicit:: How to use an existing implicit rule
8242 to get the commands for updating a file.
8243 * Catalogue of Rules:: A list of built-in implicit rules.
8244 * Implicit Variables:: How to change what predefined rules do.
8245 * Chained Rules:: How to use a chain of implicit rules.
8246 * Pattern Rules:: How to define new implicit rules.
8247 * Last Resort:: How to define commands for rules which
8249 * Suffix Rules:: The old-fashioned style of implicit rule.
8250 * Implicit Rule Search:: The precise algorithm for applying
8254 @node Using Implicit, Catalogue of Rules, Implicit Rules, Implicit Rules
8255 @section Using Implicit Rules
8256 @cindex implicit rule, how to use
8257 @cindex rule, implicit, how to use
8259 To allow @code{make} to find a customary method for updating a target file,
8260 all you have to do is refrain from specifying commands yourself. Either
8261 write a rule with no command lines, or don't write a rule at all. Then
8262 @code{make} will figure out which implicit rule to use based on which
8263 kind of source file exists or can be made.
8265 For example, suppose the makefile looks like this:
8269 cc -o foo foo.o bar.o $(CFLAGS) $(LDFLAGS)
8273 Because you mention @file{foo.o} but do not give a rule for it, @code{make}
8274 will automatically look for an implicit rule that tells how to update it.
8275 This happens whether or not the file @file{foo.o} currently exists.
8277 If an implicit rule is found, it can supply both commands and one or
8278 more prerequisites (the source files). You would want to write a rule
8279 for @file{foo.o} with no command lines if you need to specify additional
8280 prerequisites, such as header files, that the implicit rule cannot
8283 Each implicit rule has a target pattern and prerequisite patterns. There may
8284 be many implicit rules with the same target pattern. For example, numerous
8285 rules make @samp{.o} files: one, from a @samp{.c} file with the C compiler;
8286 another, from a @samp{.p} file with the Pascal compiler; and so on. The rule
8287 that actually applies is the one whose prerequisites exist or can be made.
8288 So, if you have a file @file{foo.c}, @code{make} will run the C compiler;
8289 otherwise, if you have a file @file{foo.p}, @code{make} will run the Pascal
8290 compiler; and so on.
8292 Of course, when you write the makefile, you know which implicit rule you
8293 want @code{make} to use, and you know it will choose that one because you
8294 know which possible prerequisite files are supposed to exist.
8295 @xref{Catalogue of Rules, ,Catalogue of Implicit Rules},
8296 for a catalogue of all the predefined implicit rules.
8298 Above, we said an implicit rule applies if the required prerequisites ``exist
8299 or can be made''. A file ``can be made'' if it is mentioned explicitly in
8300 the makefile as a target or a prerequisite, or if an implicit rule can be
8301 recursively found for how to make it. When an implicit prerequisite is the
8302 result of another implicit rule, we say that @dfn{chaining} is occurring.
8303 @xref{Chained Rules, ,Chains of Implicit Rules}.
8305 In general, @code{make} searches for an implicit rule for each target, and
8306 for each double-colon rule, that has no commands. A file that is mentioned
8307 only as a prerequisite is considered a target whose rule specifies nothing,
8308 so implicit rule search happens for it. @xref{Implicit Rule Search, ,Implicit Rule Search Algorithm}, for the
8309 details of how the search is done.
8311 Note that explicit prerequisites do not influence implicit rule search.
8312 For example, consider this explicit rule:
8319 The prerequisite on @file{foo.p} does not necessarily mean that
8320 @code{make} will remake @file{foo.o} according to the implicit rule to
8321 make an object file, a @file{.o} file, from a Pascal source file, a
8322 @file{.p} file. For example, if @file{foo.c} also exists, the implicit
8323 rule to make an object file from a C source file is used instead,
8324 because it appears before the Pascal rule in the list of predefined
8325 implicit rules (@pxref{Catalogue of Rules, , Catalogue of Implicit
8328 If you do not want an implicit rule to be used for a target that has no
8329 commands, you can give that target empty commands by writing a semicolon
8330 (@pxref{Empty Commands, ,Defining Empty Commands}).
8332 @node Catalogue of Rules, Implicit Variables, Using Implicit, Implicit Rules
8333 @section Catalogue of Implicit Rules
8334 @cindex implicit rule, predefined
8335 @cindex rule, implicit, predefined
8337 Here is a catalogue of predefined implicit rules which are always
8338 available unless the makefile explicitly overrides or cancels them.
8339 @xref{Canceling Rules, ,Canceling Implicit Rules}, for information on
8340 canceling or overriding an implicit rule. The @samp{-r} or
8341 @samp{--no-builtin-rules} option cancels all predefined rules.
8343 This manual only documents the default rules available on POSIX-based
8344 operating systems. Other operating systems, such as VMS, Windows,
8345 OS/2, etc. may have different sets of default rules. To see the full
8346 list of default rules and variables available in your version of GNU
8347 @code{make}, run @samp{make -p} in a directory with no makefile.
8349 Not all of these rules will always be defined, even when the @samp{-r}
8350 option is not given. Many of the predefined implicit rules are
8351 implemented in @code{make} as suffix rules, so which ones will be
8352 defined depends on the @dfn{suffix list} (the list of prerequisites of
8353 the special target @code{.SUFFIXES}). The default suffix list is:
8354 @code{.out}, @code{.a}, @code{.ln}, @code{.o}, @code{.c}, @code{.cc},
8355 @code{.C}, @code{.cpp}, @code{.p}, @code{.f}, @code{.F}, @code{.r}, @code{.y},
8356 @code{.l}, @code{.s}, @code{.S}, @code{.mod}, @code{.sym}, @code{.def},
8357 @code{.h}, @code{.info}, @code{.dvi}, @code{.tex}, @code{.texinfo},
8358 @code{.texi}, @code{.txinfo}, @code{.w}, @code{.ch} @code{.web},
8359 @code{.sh}, @code{.elc}, @code{.el}. All of the implicit rules
8360 described below whose prerequisites have one of these suffixes are
8361 actually suffix rules. If you modify the suffix list, the only
8362 predefined suffix rules in effect will be those named by one or two of
8363 the suffixes that are on the list you specify; rules whose suffixes fail
8364 to be on the list are disabled. @xref{Suffix Rules, ,Old-Fashioned
8365 Suffix Rules}, for full details on suffix rules.
8368 @item Compiling C programs
8369 @cindex C, rule to compile
8374 @file{@var{n}.o} is made automatically from @file{@var{n}.c} with
8375 a command of the form @samp{$(CC) -c $(CPPFLAGS) $(CFLAGS)}.@refill
8377 @item Compiling C++ programs
8378 @cindex C++, rule to compile
8383 @file{@var{n}.o} is made automatically from @file{@var{n}.cc},
8384 @file{@var{n}.cpp}, or @file{@var{n}.C} with a command of the form
8385 @samp{$(CXX) -c $(CPPFLAGS) $(CXXFLAGS)}. We encourage you to use the
8386 suffix @samp{.cc} for C++ source files instead of @samp{.C}.@refill
8388 @item Compiling Pascal programs
8389 @cindex Pascal, rule to compile
8392 @file{@var{n}.o} is made automatically from @file{@var{n}.p}
8393 with the command @samp{$(PC) -c $(PFLAGS)}.@refill
8395 @item Compiling Fortran and Ratfor programs
8396 @cindex Fortran, rule to compile
8397 @cindex Ratfor, rule to compile
8402 @file{@var{n}.o} is made automatically from @file{@var{n}.r},
8403 @file{@var{n}.F} or @file{@var{n}.f} by running the
8404 Fortran compiler. The precise command used is as follows:@refill
8408 @samp{$(FC) -c $(FFLAGS)}.
8410 @samp{$(FC) -c $(FFLAGS) $(CPPFLAGS)}.
8412 @samp{$(FC) -c $(FFLAGS) $(RFLAGS)}.
8415 @item Preprocessing Fortran and Ratfor programs
8416 @file{@var{n}.f} is made automatically from @file{@var{n}.r} or
8417 @file{@var{n}.F}. This rule runs just the preprocessor to convert a
8418 Ratfor or preprocessable Fortran program into a strict Fortran
8419 program. The precise command used is as follows:@refill
8423 @samp{$(FC) -F $(CPPFLAGS) $(FFLAGS)}.
8425 @samp{$(FC) -F $(FFLAGS) $(RFLAGS)}.
8428 @item Compiling Modula-2 programs
8429 @cindex Modula-2, rule to compile
8434 @file{@var{n}.sym} is made from @file{@var{n}.def} with a command
8435 of the form @samp{$(M2C) $(M2FLAGS) $(DEFFLAGS)}. @file{@var{n}.o}
8436 is made from @file{@var{n}.mod}; the form is:
8437 @w{@samp{$(M2C) $(M2FLAGS) $(MODFLAGS)}}.@refill
8440 @item Assembling and preprocessing assembler programs
8441 @cindex assembly, rule to compile
8444 @file{@var{n}.o} is made automatically from @file{@var{n}.s} by
8445 running the assembler, @code{as}. The precise command is
8446 @samp{$(AS) $(ASFLAGS)}.@refill
8449 @file{@var{n}.s} is made automatically from @file{@var{n}.S} by
8450 running the C preprocessor, @code{cpp}. The precise command is
8451 @w{@samp{$(CPP) $(CPPFLAGS)}}.
8453 @item Linking a single object file
8454 @cindex linking, predefined rule for
8457 @file{@var{n}} is made automatically from @file{@var{n}.o} by running
8458 the linker (usually called @code{ld}) via the C compiler. The precise
8459 command used is @w{@samp{$(CC) $(LDFLAGS) @var{n}.o $(LOADLIBES) $(LDLIBS)}}.
8461 This rule does the right thing for a simple program with only one
8462 source file. It will also do the right thing if there are multiple
8463 object files (presumably coming from various other source files), one
8464 of which has a name matching that of the executable file. Thus,
8471 when @file{x.c}, @file{y.c} and @file{z.c} all exist will execute:
8486 In more complicated cases, such as when there is no object file whose
8487 name derives from the executable file name, you must write an explicit
8488 command for linking.
8490 Each kind of file automatically made into @samp{.o} object files will
8491 be automatically linked by using the compiler (@samp{$(CC)},
8492 @samp{$(FC)} or @samp{$(PC)}; the C compiler @samp{$(CC)} is used to
8493 assemble @samp{.s} files) without the @samp{-c} option. This could be
8494 done by using the @samp{.o} object files as intermediates, but it is
8495 faster to do the compiling and linking in one step, so that's how it's
8498 @item Yacc for C programs
8500 @cindex Yacc, rule to run
8502 @file{@var{n}.c} is made automatically from @file{@var{n}.y} by
8503 running Yacc with the command @samp{$(YACC) $(YFLAGS)}.
8505 @item Lex for C programs
8507 @cindex Lex, rule to run
8509 @file{@var{n}.c} is made automatically from @file{@var{n}.l} by
8510 running Lex. The actual command is @samp{$(LEX) $(LFLAGS)}.
8512 @item Lex for Ratfor programs
8513 @file{@var{n}.r} is made automatically from @file{@var{n}.l} by
8514 running Lex. The actual command is @samp{$(LEX) $(LFLAGS)}.
8516 The convention of using the same suffix @samp{.l} for all Lex files
8517 regardless of whether they produce C code or Ratfor code makes it
8518 impossible for @code{make} to determine automatically which of the two
8519 languages you are using in any particular case. If @code{make} is
8520 called upon to remake an object file from a @samp{.l} file, it must
8521 guess which compiler to use. It will guess the C compiler, because
8522 that is more common. If you are using Ratfor, make sure @code{make}
8523 knows this by mentioning @file{@var{n}.r} in the makefile. Or, if you
8524 are using Ratfor exclusively, with no C files, remove @samp{.c} from
8525 the list of implicit rule suffixes with:@refill
8530 .SUFFIXES: .o .r .f .l @dots{}
8534 @item Making Lint Libraries from C, Yacc, or Lex programs
8536 @cindex @code{lint}, rule to run
8538 @file{@var{n}.ln} is made from @file{@var{n}.c} by running @code{lint}.
8539 The precise command is @w{@samp{$(LINT) $(LINTFLAGS) $(CPPFLAGS) -i}}.
8540 The same command is used on the C code produced from
8541 @file{@var{n}.y} or @file{@var{n}.l}.@refill
8543 @item @TeX{} and Web
8544 @cindex @TeX{}, rule to run
8545 @cindex Web, rule to run
8556 @file{@var{n}.dvi} is made from @file{@var{n}.tex} with the command
8557 @samp{$(TEX)}. @file{@var{n}.tex} is made from @file{@var{n}.web} with
8558 @samp{$(WEAVE)}, or from @file{@var{n}.w} (and from @file{@var{n}.ch} if
8559 it exists or can be made) with @samp{$(CWEAVE)}. @file{@var{n}.p} is
8560 made from @file{@var{n}.web} with @samp{$(TANGLE)} and @file{@var{n}.c}
8561 is made from @file{@var{n}.w} (and from @file{@var{n}.ch} if it exists
8562 or can be made) with @samp{$(CTANGLE)}.@refill
8564 @item Texinfo and Info
8565 @cindex Texinfo, rule to format
8566 @cindex Info, rule to format
8573 @file{@var{n}.dvi} is made from @file{@var{n}.texinfo},
8574 @file{@var{n}.texi}, or @file{@var{n}.txinfo}, with the command
8575 @w{@samp{$(TEXI2DVI) $(TEXI2DVI_FLAGS)}}. @file{@var{n}.info} is made from
8576 @file{@var{n}.texinfo}, @file{@var{n}.texi}, or @file{@var{n}.txinfo}, with
8577 the command @w{@samp{$(MAKEINFO) $(MAKEINFO_FLAGS)}}.
8580 @cindex RCS, rule to extract from
8582 @pindex ,v @r{(RCS file extension)}
8583 Any file @file{@var{n}} is extracted if necessary from an RCS file
8584 named either @file{@var{n},v} or @file{RCS/@var{n},v}. The precise
8585 command used is @w{@samp{$(CO) $(COFLAGS)}}. @file{@var{n}} will not be
8586 extracted from RCS if it already exists, even if the RCS file is
8587 newer. The rules for RCS are terminal
8588 (@pxref{Match-Anything Rules, ,Match-Anything Pattern Rules}),
8589 so RCS files cannot be generated from another source; they must
8590 actually exist.@refill
8593 @cindex SCCS, rule to extract from
8595 @pindex s. @r{(SCCS file prefix)}
8596 Any file @file{@var{n}} is extracted if necessary from an SCCS file
8597 named either @file{s.@var{n}} or @file{SCCS/s.@var{n}}. The precise
8598 command used is @w{@samp{$(GET) $(GFLAGS)}}. The rules for SCCS are
8599 terminal (@pxref{Match-Anything Rules, ,Match-Anything Pattern Rules}),
8600 so SCCS files cannot be generated from another source; they must
8601 actually exist.@refill
8604 For the benefit of SCCS, a file @file{@var{n}} is copied from
8605 @file{@var{n}.sh} and made executable (by everyone). This is for
8606 shell scripts that are checked into SCCS. Since RCS preserves the
8607 execution permission of a file, you do not need to use this feature
8610 We recommend that you avoid using of SCCS. RCS is widely held to be
8611 superior, and is also free. By choosing free software in place of
8612 comparable (or inferior) proprietary software, you support the free
8616 Usually, you want to change only the variables listed in the table
8617 above, which are documented in the following section.
8619 However, the commands in built-in implicit rules actually use
8620 variables such as @code{COMPILE.c}, @code{LINK.p}, and
8621 @code{PREPROCESS.S}, whose values contain the commands listed above.
8623 @code{make} follows the convention that the rule to compile a
8624 @file{.@var{x}} source file uses the variable @code{COMPILE.@var{x}}.
8625 Similarly, the rule to produce an executable from a @file{.@var{x}}
8626 file uses @code{LINK.@var{x}}; and the rule to preprocess a
8627 @file{.@var{x}} file uses @code{PREPROCESS.@var{x}}.
8629 @vindex OUTPUT_OPTION
8630 Every rule that produces an object file uses the variable
8631 @code{OUTPUT_OPTION}. @code{make} defines this variable either to
8632 contain @samp{-o $@@}, or to be empty, depending on a compile-time
8633 option. You need the @samp{-o} option to ensure that the output goes
8634 into the right file when the source file is in a different directory,
8635 as when using @code{VPATH} (@pxref{Directory Search}). However,
8636 compilers on some systems do not accept a @samp{-o} switch for object
8637 files. If you use such a system, and use @code{VPATH}, some
8638 compilations will put their output in the wrong place.
8639 A possible workaround for this problem is to give @code{OUTPUT_OPTION}
8640 the value @w{@samp{; mv $*.o $@@}}.
8642 @node Implicit Variables, Chained Rules, Catalogue of Rules, Implicit Rules
8643 @section Variables Used by Implicit Rules
8644 @cindex flags for compilers
8646 The commands in built-in implicit rules make liberal use of certain
8647 predefined variables. You can alter the values of these variables in
8648 the makefile, with arguments to @code{make}, or in the environment to
8649 alter how the implicit rules work without redefining the rules
8650 themselves. You can cancel all variables used by implicit rules with
8651 the @samp{-R} or @samp{--no-builtin-variables} option.
8653 For example, the command used to compile a C source file actually says
8654 @samp{$(CC) -c $(CFLAGS) $(CPPFLAGS)}. The default values of the variables
8655 used are @samp{cc} and nothing, resulting in the command @samp{cc -c}. By
8656 redefining @samp{CC} to @samp{ncc}, you could cause @samp{ncc} to be
8657 used for all C compilations performed by the implicit rule. By redefining
8658 @samp{CFLAGS} to be @samp{-g}, you could pass the @samp{-g} option to
8659 each compilation. @emph{All} implicit rules that do C compilation use
8660 @samp{$(CC)} to get the program name for the compiler and @emph{all}
8661 include @samp{$(CFLAGS)} among the arguments given to the compiler.@refill
8663 The variables used in implicit rules fall into two classes: those that are
8664 names of programs (like @code{CC}) and those that contain arguments for the
8665 programs (like @code{CFLAGS}). (The ``name of a program'' may also contain
8666 some command arguments, but it must start with an actual executable program
8667 name.) If a variable value contains more than one argument, separate them
8670 The following tables describe of some of the more commonly-used predefined
8671 variables. This list is not exhaustive, and the default values shown here may
8672 not be what are selected by @code{make} for your environment. To see the
8673 complete list of predefined variables for your instance of GNU @code{make} you
8674 can run @samp{make -p} in a directory with no makefiles.
8676 Here is a table of some of the more common variables used as names of
8677 programs in built-in rules:
8683 Archive-maintaining program; default @samp{ar}.
8688 Program for compiling assembly files; default @samp{as}.
8693 Program for compiling C programs; default @samp{cc}.
8698 Program for checking out files from RCS; default @samp{co}.
8703 Program for compiling C++ programs; default @samp{g++}.
8708 Program for extracting a file from RCS; default @samp{co}.
8713 Program for running the C preprocessor, with results to standard output;
8714 default @samp{$(CC) -E}.
8718 Program for compiling or preprocessing Fortran and Ratfor programs;
8724 Program for extracting a file from SCCS; default @samp{get}.
8729 Program to use to turn Lex grammars into source code; default @samp{lex}.
8734 Program to use to turn Yacc grammars into source code; default @samp{yacc}.
8739 Program to use to run lint on source code; default @samp{lint}.
8744 Program to use to compile Modula-2 source code; default @samp{m2c}.
8749 Program for compiling Pascal programs; default @samp{pc}.
8754 Program to convert a Texinfo source file into an Info file; default
8760 Program to make @TeX{} @sc{dvi} files from @TeX{} source;
8766 Program to make @TeX{} @sc{dvi} files from Texinfo source;
8767 default @samp{texi2dvi}.
8772 Program to translate Web into @TeX{}; default @samp{weave}.
8777 Program to translate C Web into @TeX{}; default @samp{cweave}.
8782 Program to translate Web into Pascal; default @samp{tangle}.
8787 Program to translate C Web into C; default @samp{ctangle}.
8792 Command to remove a file; default @samp{rm -f}.
8796 Here is a table of variables whose values are additional arguments for the
8797 programs above. The default values for all of these is the empty
8798 string, unless otherwise noted.
8803 Flags to give the archive-maintaining program; default @samp{rv}.
8807 Extra flags to give to the assembler (when explicitly
8808 invoked on a @samp{.s} or @samp{.S} file).
8812 Extra flags to give to the C compiler.
8816 Extra flags to give to the C++ compiler.
8820 Extra flags to give to the RCS @code{co} program.
8824 Extra flags to give to the C preprocessor and programs
8825 that use it (the C and Fortran compilers).
8829 Extra flags to give to the Fortran compiler.
8833 Extra flags to give to the SCCS @code{get} program.
8837 Extra flags to give to compilers when they are supposed to invoke the linker,
8842 Extra flags to give to Lex.
8846 Extra flags to give to Yacc.
8850 Extra flags to give to the Pascal compiler.
8854 Extra flags to give to the Fortran compiler for Ratfor programs.
8858 Extra flags to give to lint.
8861 @node Chained Rules, Pattern Rules, Implicit Variables, Implicit Rules
8862 @section Chains of Implicit Rules
8864 @cindex chains of rules
8865 @cindex rule, implicit, chains of
8866 Sometimes a file can be made by a sequence of implicit rules. For example,
8867 a file @file{@var{n}.o} could be made from @file{@var{n}.y} by running
8868 first Yacc and then @code{cc}. Such a sequence is called a @dfn{chain}.
8870 If the file @file{@var{n}.c} exists, or is mentioned in the makefile, no
8871 special searching is required: @code{make} finds that the object file can
8872 be made by C compilation from @file{@var{n}.c}; later on, when considering
8873 how to make @file{@var{n}.c}, the rule for running Yacc is
8874 used. Ultimately both @file{@var{n}.c} and @file{@var{n}.o} are
8877 @cindex intermediate files
8878 @cindex files, intermediate
8879 However, even if @file{@var{n}.c} does not exist and is not mentioned,
8880 @code{make} knows how to envision it as the missing link between
8881 @file{@var{n}.o} and @file{@var{n}.y}! In this case, @file{@var{n}.c} is
8882 called an @dfn{intermediate file}. Once @code{make} has decided to use the
8883 intermediate file, it is entered in the data base as if it had been
8884 mentioned in the makefile, along with the implicit rule that says how to
8887 Intermediate files are remade using their rules just like all other
8888 files. But intermediate files are treated differently in two ways.
8890 The first difference is what happens if the intermediate file does not
8891 exist. If an ordinary file @var{b} does not exist, and @code{make}
8892 considers a target that depends on @var{b}, it invariably creates
8893 @var{b} and then updates the target from @var{b}. But if @var{b} is an
8894 intermediate file, then @code{make} can leave well enough alone. It
8895 won't bother updating @var{b}, or the ultimate target, unless some
8896 prerequisite of @var{b} is newer than that target or there is some other
8897 reason to update that target.
8899 The second difference is that if @code{make} @emph{does} create @var{b}
8900 in order to update something else, it deletes @var{b} later on after it
8901 is no longer needed. Therefore, an intermediate file which did not
8902 exist before @code{make} also does not exist after @code{make}.
8903 @code{make} reports the deletion to you by printing a @samp{rm -f}
8904 command showing which file it is deleting.
8906 Ordinarily, a file cannot be intermediate if it is mentioned in the
8907 makefile as a target or prerequisite. However, you can explicitly mark a
8908 file as intermediate by listing it as a prerequisite of the special target
8909 @code{.INTERMEDIATE}. This takes effect even if the file is mentioned
8910 explicitly in some other way.
8912 @cindex intermediate files, preserving
8913 @cindex preserving intermediate files
8914 @cindex secondary files
8915 You can prevent automatic deletion of an intermediate file by marking it
8916 as a @dfn{secondary} file. To do this, list it as a prerequisite of the
8917 special target @code{.SECONDARY}. When a file is secondary, @code{make}
8918 will not create the file merely because it does not already exist, but
8919 @code{make} does not automatically delete the file. Marking a file as
8920 secondary also marks it as intermediate.
8922 You can list the target pattern of an implicit rule (such as @samp{%.o})
8923 as a prerequisite of the special target @code{.PRECIOUS} to preserve
8924 intermediate files made by implicit rules whose target patterns match
8925 that file's name; see @ref{Interrupts}.@refill
8926 @cindex preserving with @code{.PRECIOUS}
8927 @cindex @code{.PRECIOUS} intermediate files
8929 A chain can involve more than two implicit rules. For example, it is
8930 possible to make a file @file{foo} from @file{RCS/foo.y,v} by running RCS,
8931 Yacc and @code{cc}. Then both @file{foo.y} and @file{foo.c} are
8932 intermediate files that are deleted at the end.@refill
8934 No single implicit rule can appear more than once in a chain. This means
8935 that @code{make} will not even consider such a ridiculous thing as making
8936 @file{foo} from @file{foo.o.o} by running the linker twice. This
8937 constraint has the added benefit of preventing any infinite loop in the
8938 search for an implicit rule chain.
8940 There are some special implicit rules to optimize certain cases that would
8941 otherwise be handled by rule chains. For example, making @file{foo} from
8942 @file{foo.c} could be handled by compiling and linking with separate
8943 chained rules, using @file{foo.o} as an intermediate file. But what
8944 actually happens is that a special rule for this case does the compilation
8945 and linking with a single @code{cc} command. The optimized rule is used in
8946 preference to the step-by-step chain because it comes earlier in the
8949 @node Pattern Rules, Last Resort, Chained Rules, Implicit Rules
8950 @section Defining and Redefining Pattern Rules
8952 You define an implicit rule by writing a @dfn{pattern rule}. A pattern
8953 rule looks like an ordinary rule, except that its target contains the
8954 character @samp{%} (exactly one of them). The target is considered a
8955 pattern for matching file names; the @samp{%} can match any nonempty
8956 substring, while other characters match only themselves. The prerequisites
8957 likewise use @samp{%} to show how their names relate to the target name.
8959 Thus, a pattern rule @samp{%.o : %.c} says how to make any file
8960 @file{@var{stem}.o} from another file @file{@var{stem}.c}.@refill
8962 Note that expansion using @samp{%} in pattern rules occurs
8963 @strong{after} any variable or function expansions, which take place
8964 when the makefile is read. @xref{Using Variables, , How to Use
8965 Variables}, and @ref{Functions, ,Functions for Transforming Text}.
8968 * Pattern Intro:: An introduction to pattern rules.
8969 * Pattern Examples:: Examples of pattern rules.
8970 * Automatic Variables:: How to use automatic variables in the
8971 commands of implicit rules.
8972 * Pattern Match:: How patterns match.
8973 * Match-Anything Rules:: Precautions you should take prior to
8974 defining rules that can match any
8975 target file whatever.
8976 * Canceling Rules:: How to override or cancel built-in rules.
8979 @node Pattern Intro, Pattern Examples, Pattern Rules, Pattern Rules
8980 @subsection Introduction to Pattern Rules
8981 @cindex pattern rule
8982 @cindex rule, pattern
8984 A pattern rule contains the character @samp{%} (exactly one of them)
8985 in the target; otherwise, it looks exactly like an ordinary rule. The
8986 target is a pattern for matching file names; the @samp{%} matches any
8987 nonempty substring, while other characters match only themselves.
8988 @cindex target pattern, implicit
8989 @cindex @code{%}, in pattern rules
8991 For example, @samp{%.c} as a pattern matches any file name that ends in
8992 @samp{.c}. @samp{s.%.c} as a pattern matches any file name that starts
8993 with @samp{s.}, ends in @samp{.c} and is at least five characters long.
8994 (There must be at least one character to match the @samp{%}.) The substring
8995 that the @samp{%} matches is called the @dfn{stem}.@refill
8997 @samp{%} in a prerequisite of a pattern rule stands for the same stem
8998 that was matched by the @samp{%} in the target. In order for the
8999 pattern rule to apply, its target pattern must match the file name
9000 under consideration and all of its prerequisites (after pattern
9001 substitution) must name files that exist or can be made. These files
9002 become prerequisites of the target.
9003 @cindex prerequisite pattern, implicit
9005 Thus, a rule of the form
9008 %.o : %.c ; @var{command}@dots{}
9012 specifies how to make a file @file{@var{n}.o}, with another file
9013 @file{@var{n}.c} as its prerequisite, provided that @file{@var{n}.c}
9014 exists or can be made.
9016 There may also be prerequisites that do not use @samp{%}; such a prerequisite
9017 attaches to every file made by this pattern rule. These unvarying
9018 prerequisites are useful occasionally.
9020 A pattern rule need not have any prerequisites that contain @samp{%}, or
9021 in fact any prerequisites at all. Such a rule is effectively a general
9022 wildcard. It provides a way to make any file that matches the target
9023 pattern. @xref{Last Resort}.
9025 @c !!! The end of of this paragraph should be rewritten. --bob
9026 Pattern rules may have more than one target. Unlike normal rules, this
9027 does not act as many different rules with the same prerequisites and
9028 commands. If a pattern rule has multiple targets, @code{make} knows that
9029 the rule's commands are responsible for making all of the targets. The
9030 commands are executed only once to make all the targets. When searching
9031 for a pattern rule to match a target, the target patterns of a rule other
9032 than the one that matches the target in need of a rule are incidental:
9033 @code{make} worries only about giving commands and prerequisites to the file
9034 presently in question. However, when this file's commands are run, the
9035 other targets are marked as having been updated themselves.
9036 @cindex multiple targets, in pattern rule
9037 @cindex target, multiple in pattern rule
9039 The order in which pattern rules appear in the makefile is important
9040 since this is the order in which they are considered.
9041 Of equally applicable
9042 rules, only the first one found is used. The rules you write take precedence
9043 over those that are built in. Note however, that a rule whose
9044 prerequisites actually exist or are mentioned always takes priority over a
9045 rule with prerequisites that must be made by chaining other implicit rules.
9046 @cindex pattern rules, order of
9047 @cindex order of pattern rules
9049 @node Pattern Examples, Automatic Variables, Pattern Intro, Pattern Rules
9050 @subsection Pattern Rule Examples
9052 Here are some examples of pattern rules actually predefined in
9053 @code{make}. First, the rule that compiles @samp{.c} files into @samp{.o}
9058 $(CC) -c $(CFLAGS) $(CPPFLAGS) $< -o $@@
9062 defines a rule that can make any file @file{@var{x}.o} from
9063 @file{@var{x}.c}. The command uses the automatic variables @samp{$@@} and
9064 @samp{$<} to substitute the names of the target file and the source file
9065 in each case where the rule applies (@pxref{Automatic Variables}).@refill
9067 Here is a second built-in rule:
9075 defines a rule that can make any file @file{@var{x}} whatsoever from a
9076 corresponding file @file{@var{x},v} in the subdirectory @file{RCS}. Since
9077 the target is @samp{%}, this rule will apply to any file whatever, provided
9078 the appropriate prerequisite file exists. The double colon makes the rule
9079 @dfn{terminal}, which means that its prerequisite may not be an intermediate
9080 file (@pxref{Match-Anything Rules, ,Match-Anything Pattern Rules}).@refill
9083 This pattern rule has two targets:
9087 %.tab.c %.tab.h: %.y
9093 @c The following paragraph is rewritten to avoid overfull hboxes
9094 This tells @code{make} that the command @samp{bison -d @var{x}.y} will
9095 make both @file{@var{x}.tab.c} and @file{@var{x}.tab.h}. If the file
9096 @file{foo} depends on the files @file{parse.tab.o} and @file{scan.o}
9097 and the file @file{scan.o} depends on the file @file{parse.tab.h},
9098 when @file{parse.y} is changed, the command @samp{bison -d parse.y}
9099 will be executed only once, and the prerequisites of both
9100 @file{parse.tab.o} and @file{scan.o} will be satisfied. (Presumably
9101 the file @file{parse.tab.o} will be recompiled from @file{parse.tab.c}
9102 and the file @file{scan.o} from @file{scan.c}, while @file{foo} is
9103 linked from @file{parse.tab.o}, @file{scan.o}, and its other
9104 prerequisites, and it will execute happily ever after.)@refill
9106 @node Automatic Variables, Pattern Match, Pattern Examples, Pattern Rules
9107 @subsection Automatic Variables
9108 @cindex automatic variables
9109 @cindex variables, automatic
9110 @cindex variables, and implicit rule
9112 Suppose you are writing a pattern rule to compile a @samp{.c} file into a
9113 @samp{.o} file: how do you write the @samp{cc} command so that it operates
9114 on the right source file name? You cannot write the name in the command,
9115 because the name is different each time the implicit rule is applied.
9117 What you do is use a special feature of @code{make}, the @dfn{automatic
9118 variables}. These variables have values computed afresh for each rule that
9119 is executed, based on the target and prerequisites of the rule. In this
9120 example, you would use @samp{$@@} for the object file name and @samp{$<}
9121 for the source file name.
9123 @cindex automatic variables in prerequisites
9124 @cindex prerequisites, and automatic variables
9125 It's very important that you recognize the limited scope in which
9126 automatic variable values are available: they only have values within
9127 the command script. In particular, you cannot use them anywhere
9128 within the target list of a rule; they have no value there and will
9129 expand to the empty string. Also, they cannot be accessed directly
9130 within the prerequisite list of a rule. A common mistake is
9131 attempting to use @code{$@@} within the prerequisites list; this will
9132 not work. However, there is a special feature of GNU @code{make},
9133 secondary expansion (@pxref{Secondary Expansion}), which will allow
9134 automatic variable values to be used in prerequisite lists.
9136 Here is a table of automatic variables:
9140 @vindex @@ @r{(automatic variable)}
9142 The file name of the target of the rule. If the target is an archive
9143 member, then @samp{$@@} is the name of the archive file. In a pattern
9144 rule that has multiple targets (@pxref{Pattern Intro, ,Introduction to
9145 Pattern Rules}), @samp{$@@} is the name of whichever target caused the
9146 rule's commands to be run.
9149 @vindex % @r{(automatic variable)}
9151 The target member name, when the target is an archive member.
9152 @xref{Archives}. For example, if the target is @file{foo.a(bar.o)} then
9153 @samp{$%} is @file{bar.o} and @samp{$@@} is @file{foo.a}. @samp{$%} is
9154 empty when the target is not an archive member.
9157 @vindex < @r{(automatic variable)}
9159 The name of the first prerequisite. If the target got its commands from
9160 an implicit rule, this will be the first prerequisite added by the
9161 implicit rule (@pxref{Implicit Rules}).
9164 @vindex ? @r{(automatic variable)}
9166 The names of all the prerequisites that are newer than the target, with
9167 spaces between them. For prerequisites which are archive members, only
9168 the member named is used (@pxref{Archives}).
9169 @cindex prerequisites, list of changed
9170 @cindex list of changed prerequisites
9173 @vindex ^ @r{(automatic variable)}
9175 The names of all the prerequisites, with spaces between them. For
9176 prerequisites which are archive members, only the member named is used
9177 (@pxref{Archives}). A target has only one prerequisite on each other file
9178 it depends on, no matter how many times each file is listed as a
9179 prerequisite. So if you list a prerequisite more than once for a target,
9180 the value of @code{$^} contains just one copy of the name. This list
9181 does @strong{not} contain any of the order-only prerequisites; for those
9182 see the @samp{$|} variable, below.
9183 @cindex prerequisites, list of all
9184 @cindex list of all prerequisites
9187 @vindex + @r{(automatic variable)}
9189 This is like @samp{$^}, but prerequisites listed more than once are
9190 duplicated in the order they were listed in the makefile. This is
9191 primarily useful for use in linking commands where it is meaningful to
9192 repeat library file names in a particular order.
9195 @vindex | @r{(automatic variable)}
9197 The names of all the order-only prerequisites, with spaces between
9201 @vindex * @r{(automatic variable)}
9203 The stem with which an implicit rule matches (@pxref{Pattern Match, ,How
9204 Patterns Match}). If the target is @file{dir/a.foo.b} and the target
9205 pattern is @file{a.%.b} then the stem is @file{dir/foo}. The stem is
9206 useful for constructing names of related files.@refill
9207 @cindex stem, variable for
9209 In a static pattern rule, the stem is part of the file name that matched
9210 the @samp{%} in the target pattern.
9212 In an explicit rule, there is no stem; so @samp{$*} cannot be determined
9213 in that way. Instead, if the target name ends with a recognized suffix
9214 (@pxref{Suffix Rules, ,Old-Fashioned Suffix Rules}), @samp{$*} is set to
9215 the target name minus the suffix. For example, if the target name is
9216 @samp{foo.c}, then @samp{$*} is set to @samp{foo}, since @samp{.c} is a
9217 suffix. GNU @code{make} does this bizarre thing only for compatibility
9218 with other implementations of @code{make}. You should generally avoid
9219 using @samp{$*} except in implicit rules or static pattern rules.@refill
9221 If the target name in an explicit rule does not end with a recognized
9222 suffix, @samp{$*} is set to the empty string for that rule.
9225 @samp{$?} is useful even in explicit rules when you wish to operate on only
9226 the prerequisites that have changed. For example, suppose that an archive
9227 named @file{lib} is supposed to contain copies of several object files.
9228 This rule copies just the changed object files into the archive:
9232 lib: foo.o bar.o lose.o win.o
9237 Of the variables listed above, four have values that are single file
9238 names, and three have values that are lists of file names. These seven
9239 have variants that get just the file's directory name or just the file
9240 name within the directory. The variant variables' names are formed by
9241 appending @samp{D} or @samp{F}, respectively. These variants are
9242 semi-obsolete in GNU @code{make} since the functions @code{dir} and
9243 @code{notdir} can be used to get a similar effect (@pxref{File Name
9244 Functions, , Functions for File Names}). Note, however, that the
9245 @samp{D} variants all omit the trailing slash which always appears in
9246 the output of the @code{dir} function. Here is a table of the variants:
9250 @vindex @@D @r{(automatic variable)}
9252 The directory part of the file name of the target, with the trailing
9253 slash removed. If the value of @samp{$@@} is @file{dir/foo.o} then
9254 @samp{$(@@D)} is @file{dir}. This value is @file{.} if @samp{$@@} does
9255 not contain a slash.
9258 @vindex @@F @r{(automatic variable)}
9260 The file-within-directory part of the file name of the target. If the
9261 value of @samp{$@@} is @file{dir/foo.o} then @samp{$(@@F)} is
9262 @file{foo.o}. @samp{$(@@F)} is equivalent to @samp{$(notdir $@@)}.
9265 @vindex *D @r{(automatic variable)}
9268 @vindex *F @r{(automatic variable)}
9270 The directory part and the file-within-directory
9271 part of the stem; @file{dir} and @file{foo} in this example.
9274 @vindex %D @r{(automatic variable)}
9277 @vindex %F @r{(automatic variable)}
9279 The directory part and the file-within-directory part of the target
9280 archive member name. This makes sense only for archive member targets
9281 of the form @file{@var{archive}(@var{member})} and is useful only when
9282 @var{member} may contain a directory name. (@xref{Archive Members,
9283 ,Archive Members as Targets}.)
9286 @vindex <D @r{(automatic variable)}
9289 @vindex <F @r{(automatic variable)}
9291 The directory part and the file-within-directory
9292 part of the first prerequisite.
9295 @vindex ^D @r{(automatic variable)}
9298 @vindex ^F @r{(automatic variable)}
9300 Lists of the directory parts and the file-within-directory
9301 parts of all prerequisites.
9304 @vindex +D @r{(automatic variable)}
9307 @vindex +F @r{(automatic variable)}
9309 Lists of the directory parts and the file-within-directory
9310 parts of all prerequisites, including multiple instances of duplicated
9314 @vindex ?D @r{(automatic variable)}
9317 @vindex ?F @r{(automatic variable)}
9319 Lists of the directory parts and the file-within-directory parts of
9320 all prerequisites that are newer than the target.
9323 Note that we use a special stylistic convention when we talk about these
9324 automatic variables; we write ``the value of @samp{$<}'', rather than
9325 @w{``the variable @code{<}''} as we would write for ordinary variables
9326 such as @code{objects} and @code{CFLAGS}. We think this convention
9327 looks more natural in this special case. Please do not assume it has a
9328 deep significance; @samp{$<} refers to the variable named @code{<} just
9329 as @samp{$(CFLAGS)} refers to the variable named @code{CFLAGS}.
9330 You could just as well use @samp{$(<)} in place of @samp{$<}.
9332 @node Pattern Match, Match-Anything Rules, Automatic Variables, Pattern Rules
9333 @subsection How Patterns Match
9336 A target pattern is composed of a @samp{%} between a prefix and a suffix,
9337 either or both of which may be empty. The pattern matches a file name only
9338 if the file name starts with the prefix and ends with the suffix, without
9339 overlap. The text between the prefix and the suffix is called the
9340 @dfn{stem}. Thus, when the pattern @samp{%.o} matches the file name
9341 @file{test.o}, the stem is @samp{test}. The pattern rule prerequisites are
9342 turned into actual file names by substituting the stem for the character
9343 @samp{%}. Thus, if in the same example one of the prerequisites is written
9344 as @samp{%.c}, it expands to @samp{test.c}.@refill
9346 When the target pattern does not contain a slash (and it usually does
9347 not), directory names in the file names are removed from the file name
9348 before it is compared with the target prefix and suffix. After the
9349 comparison of the file name to the target pattern, the directory
9350 names, along with the slash that ends them, are added on to the
9351 prerequisite file names generated from the pattern rule's prerequisite
9352 patterns and the file name. The directories are ignored only for the
9353 purpose of finding an implicit rule to use, not in the application of
9354 that rule. Thus, @samp{e%t} matches the file name @file{src/eat},
9355 with @samp{src/a} as the stem. When prerequisites are turned into file
9356 names, the directories from the stem are added at the front, while the
9357 rest of the stem is substituted for the @samp{%}. The stem
9358 @samp{src/a} with a prerequisite pattern @samp{c%r} gives the file name
9359 @file{src/car}.@refill
9361 @node Match-Anything Rules, Canceling Rules, Pattern Match, Pattern Rules
9362 @subsection Match-Anything Pattern Rules
9364 @cindex match-anything rule
9365 @cindex terminal rule
9366 When a pattern rule's target is just @samp{%}, it matches any file name
9367 whatever. We call these rules @dfn{match-anything} rules. They are very
9368 useful, but it can take a lot of time for @code{make} to think about them,
9369 because it must consider every such rule for each file name listed either
9370 as a target or as a prerequisite.
9372 Suppose the makefile mentions @file{foo.c}. For this target, @code{make}
9373 would have to consider making it by linking an object file @file{foo.c.o},
9374 or by C compilation-and-linking in one step from @file{foo.c.c}, or by
9375 Pascal compilation-and-linking from @file{foo.c.p}, and many other
9378 We know these possibilities are ridiculous since @file{foo.c} is a C source
9379 file, not an executable. If @code{make} did consider these possibilities,
9380 it would ultimately reject them, because files such as @file{foo.c.o} and
9381 @file{foo.c.p} would not exist. But these possibilities are so
9382 numerous that @code{make} would run very slowly if it had to consider
9385 To gain speed, we have put various constraints on the way @code{make}
9386 considers match-anything rules. There are two different constraints that
9387 can be applied, and each time you define a match-anything rule you must
9388 choose one or the other for that rule.
9390 One choice is to mark the match-anything rule as @dfn{terminal} by defining
9391 it with a double colon. When a rule is terminal, it does not apply unless
9392 its prerequisites actually exist. Prerequisites that could be made with
9393 other implicit rules are not good enough. In other words, no further
9394 chaining is allowed beyond a terminal rule.
9396 For example, the built-in implicit rules for extracting sources from RCS
9397 and SCCS files are terminal; as a result, if the file @file{foo.c,v} does
9398 not exist, @code{make} will not even consider trying to make it as an
9399 intermediate file from @file{foo.c,v.o} or from @file{RCS/SCCS/s.foo.c,v}.
9400 RCS and SCCS files are generally ultimate source files, which should not be
9401 remade from any other files; therefore, @code{make} can save time by not
9402 looking for ways to remake them.@refill
9404 If you do not mark the match-anything rule as terminal, then it is
9405 nonterminal. A nonterminal match-anything rule cannot apply to a file name
9406 that indicates a specific type of data. A file name indicates a specific
9407 type of data if some non-match-anything implicit rule target matches it.
9409 For example, the file name @file{foo.c} matches the target for the pattern
9410 rule @samp{%.c : %.y} (the rule to run Yacc). Regardless of whether this
9411 rule is actually applicable (which happens only if there is a file
9412 @file{foo.y}), the fact that its target matches is enough to prevent
9413 consideration of any nonterminal match-anything rules for the file
9414 @file{foo.c}. Thus, @code{make} will not even consider trying to make
9415 @file{foo.c} as an executable file from @file{foo.c.o}, @file{foo.c.c},
9416 @file{foo.c.p}, etc.@refill
9418 The motivation for this constraint is that nonterminal match-anything
9419 rules are used for making files containing specific types of data (such as
9420 executable files) and a file name with a recognized suffix indicates some
9421 other specific type of data (such as a C source file).
9423 Special built-in dummy pattern rules are provided solely to recognize
9424 certain file names so that nonterminal match-anything rules will not be
9425 considered. These dummy rules have no prerequisites and no commands, and
9426 they are ignored for all other purposes. For example, the built-in
9434 exists to make sure that Pascal source files such as @file{foo.p} match a
9435 specific target pattern and thereby prevent time from being wasted looking
9436 for @file{foo.p.o} or @file{foo.p.c}.
9438 Dummy pattern rules such as the one for @samp{%.p} are made for every
9439 suffix listed as valid for use in suffix rules (@pxref{Suffix Rules, ,Old-Fashioned Suffix Rules}).
9441 @node Canceling Rules, , Match-Anything Rules, Pattern Rules
9442 @subsection Canceling Implicit Rules
9444 You can override a built-in implicit rule (or one you have defined
9445 yourself) by defining a new pattern rule with the same target and
9446 prerequisites, but different commands. When the new rule is defined, the
9447 built-in one is replaced. The new rule's position in the sequence of
9448 implicit rules is determined by where you write the new rule.
9450 You can cancel a built-in implicit rule by defining a pattern rule with the
9451 same target and prerequisites, but no commands. For example, the following
9452 would cancel the rule that runs the assembler:
9458 @node Last Resort, Suffix Rules, Pattern Rules, Implicit Rules
9459 @section Defining Last-Resort Default Rules
9460 @cindex last-resort default rules
9461 @cindex default rules, last-resort
9463 You can define a last-resort implicit rule by writing a terminal
9464 match-anything pattern rule with no prerequisites (@pxref{Match-Anything
9465 Rules}). This is just like any other pattern rule; the only thing
9466 special about it is that it will match any target. So such a rule's
9467 commands are used for all targets and prerequisites that have no commands
9468 of their own and for which no other implicit rule applies.
9470 For example, when testing a makefile, you might not care if the source
9471 files contain real data, only that they exist. Then you might do this:
9479 to cause all the source files needed (as prerequisites) to be created
9483 You can instead define commands to be used for targets for which there
9484 are no rules at all, even ones which don't specify commands. You do
9485 this by writing a rule for the target @code{.DEFAULT}. Such a rule's
9486 commands are used for all prerequisites which do not appear as targets in
9487 any explicit rule, and for which no implicit rule applies. Naturally,
9488 there is no @code{.DEFAULT} rule unless you write one.
9490 If you use @code{.DEFAULT} with no commands or prerequisites:
9497 the commands previously stored for @code{.DEFAULT} are cleared.
9498 Then @code{make} acts as if you had never defined @code{.DEFAULT} at all.
9500 If you do not want a target to get the commands from a match-anything
9501 pattern rule or @code{.DEFAULT}, but you also do not want any commands
9502 to be run for the target, you can give it empty commands (@pxref{Empty
9503 Commands, ,Defining Empty Commands}).@refill
9505 You can use a last-resort rule to override part of another makefile.
9506 @xref{Overriding Makefiles, , Overriding Part of Another Makefile}.
9508 @node Suffix Rules, Implicit Rule Search, Last Resort, Implicit Rules
9509 @section Old-Fashioned Suffix Rules
9510 @cindex old-fashioned suffix rules
9513 @dfn{Suffix rules} are the old-fashioned way of defining implicit rules for
9514 @code{make}. Suffix rules are obsolete because pattern rules are more
9515 general and clearer. They are supported in GNU @code{make} for
9516 compatibility with old makefiles. They come in two kinds:
9517 @dfn{double-suffix} and @dfn{single-suffix}.@refill
9519 A double-suffix rule is defined by a pair of suffixes: the target suffix
9520 and the source suffix. It matches any file whose name ends with the
9521 target suffix. The corresponding implicit prerequisite is made by
9522 replacing the target suffix with the source suffix in the file name. A
9523 two-suffix rule whose target and source suffixes are @samp{.o} and
9524 @samp{.c} is equivalent to the pattern rule @samp{%.o : %.c}.
9526 A single-suffix rule is defined by a single suffix, which is the source
9527 suffix. It matches any file name, and the corresponding implicit
9528 prerequisite name is made by appending the source suffix. A single-suffix
9529 rule whose source suffix is @samp{.c} is equivalent to the pattern rule
9532 Suffix rule definitions are recognized by comparing each rule's target
9533 against a defined list of known suffixes. When @code{make} sees a rule
9534 whose target is a known suffix, this rule is considered a single-suffix
9535 rule. When @code{make} sees a rule whose target is two known suffixes
9536 concatenated, this rule is taken as a double-suffix rule.
9538 For example, @samp{.c} and @samp{.o} are both on the default list of
9539 known suffixes. Therefore, if you define a rule whose target is
9540 @samp{.c.o}, @code{make} takes it to be a double-suffix rule with source
9541 suffix @samp{.c} and target suffix @samp{.o}. Here is the old-fashioned
9542 way to define the rule for compiling a C source file:@refill
9546 $(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@@ $<
9549 Suffix rules cannot have any prerequisites of their own. If they have any,
9550 they are treated as normal files with funny names, not as suffix rules.
9555 $(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@@ $<
9559 tells how to make the file @file{.c.o} from the prerequisite file
9560 @file{foo.h}, and is not at all like the pattern rule:
9564 $(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@@ $<
9568 which tells how to make @samp{.o} files from @samp{.c} files, and makes all
9569 @samp{.o} files using this pattern rule also depend on @file{foo.h}.
9571 Suffix rules with no commands are also meaningless. They do not remove
9572 previous rules as do pattern rules with no commands (@pxref{Canceling
9573 Rules, , Canceling Implicit Rules}). They simply enter the suffix or pair of suffixes concatenated as
9574 a target in the data base.@refill
9577 The known suffixes are simply the names of the prerequisites of the special
9578 target @code{.SUFFIXES}. You can add your own suffixes by writing a rule
9579 for @code{.SUFFIXES} that adds more prerequisites, as in:
9582 .SUFFIXES: .hack .win
9586 which adds @samp{.hack} and @samp{.win} to the end of the list of suffixes.
9588 If you wish to eliminate the default known suffixes instead of just adding
9589 to them, write a rule for @code{.SUFFIXES} with no prerequisites. By
9590 special dispensation, this eliminates all existing prerequisites of
9591 @code{.SUFFIXES}. You can then write another rule to add the suffixes you
9596 .SUFFIXES: # @r{Delete the default suffixes}
9597 .SUFFIXES: .c .o .h # @r{Define our suffix list}
9601 The @samp{-r} or @samp{--no-builtin-rules} flag causes the default
9602 list of suffixes to be empty.
9605 The variable @code{SUFFIXES} is defined to the default list of suffixes
9606 before @code{make} reads any makefiles. You can change the list of suffixes
9607 with a rule for the special target @code{.SUFFIXES}, but that does not alter
9610 @node Implicit Rule Search, , Suffix Rules, Implicit Rules
9611 @section Implicit Rule Search Algorithm
9612 @cindex implicit rule, search algorithm
9613 @cindex search algorithm, implicit rule
9615 Here is the procedure @code{make} uses for searching for an implicit rule
9616 for a target @var{t}. This procedure is followed for each double-colon
9617 rule with no commands, for each target of ordinary rules none of which have
9618 commands, and for each prerequisite that is not the target of any rule. It
9619 is also followed recursively for prerequisites that come from implicit
9620 rules, in the search for a chain of rules.
9622 Suffix rules are not mentioned in this algorithm because suffix rules are
9623 converted to equivalent pattern rules once the makefiles have been read in.
9625 For an archive member target of the form
9626 @samp{@var{archive}(@var{member})}, the following algorithm is run
9627 twice, first using the entire target name @var{t}, and second using
9628 @samp{(@var{member})} as the target @var{t} if the first run found no
9633 Split @var{t} into a directory part, called @var{d}, and the rest,
9634 called @var{n}. For example, if @var{t} is @samp{src/foo.o}, then
9635 @var{d} is @samp{src/} and @var{n} is @samp{foo.o}.@refill
9638 Make a list of all the pattern rules one of whose targets matches
9639 @var{t} or @var{n}. If the target pattern contains a slash, it is
9640 matched against @var{t}; otherwise, against @var{n}.
9643 If any rule in that list is @emph{not} a match-anything rule, then
9644 remove all nonterminal match-anything rules from the list.
9647 Remove from the list all rules with no commands.
9650 For each pattern rule in the list:
9654 Find the stem @var{s}, which is the nonempty part of @var{t} or @var{n}
9655 matched by the @samp{%} in the target pattern.@refill
9658 Compute the prerequisite names by substituting @var{s} for @samp{%}; if
9659 the target pattern does not contain a slash, append @var{d} to
9660 the front of each prerequisite name.@refill
9663 Test whether all the prerequisites exist or ought to exist. (If a
9664 file name is mentioned in the makefile as a target or as an explicit
9665 prerequisite, then we say it ought to exist.)
9667 If all prerequisites exist or ought to exist, or there are no prerequisites,
9668 then this rule applies.
9672 If no pattern rule has been found so far, try harder.
9673 For each pattern rule in the list:
9677 If the rule is terminal, ignore it and go on to the next rule.
9680 Compute the prerequisite names as before.
9683 Test whether all the prerequisites exist or ought to exist.
9686 For each prerequisite that does not exist, follow this algorithm
9687 recursively to see if the prerequisite can be made by an implicit
9691 If all prerequisites exist, ought to exist, or can be
9692 made by implicit rules, then this rule applies.
9696 If no implicit rule applies, the rule for @code{.DEFAULT}, if any,
9697 applies. In that case, give @var{t} the same commands that
9698 @code{.DEFAULT} has. Otherwise, there are no commands for @var{t}.
9701 Once a rule that applies has been found, for each target pattern of the
9702 rule other than the one that matched @var{t} or @var{n}, the @samp{%} in
9703 the pattern is replaced with @var{s} and the resultant file name is stored
9704 until the commands to remake the target file @var{t} are executed. After
9705 these commands are executed, each of these stored file names are entered
9706 into the data base and marked as having been updated and having the same
9707 update status as the file @var{t}.
9709 When the commands of a pattern rule are executed for @var{t}, the automatic
9710 variables are set corresponding to the target and prerequisites.
9711 @xref{Automatic Variables}.
9713 @node Archives, Features, Implicit Rules, Top
9714 @chapter Using @code{make} to Update Archive Files
9717 @dfn{Archive files} are files containing named subfiles called
9718 @dfn{members}; they are maintained with the program @code{ar} and their
9719 main use is as subroutine libraries for linking.
9722 * Archive Members:: Archive members as targets.
9723 * Archive Update:: The implicit rule for archive member targets.
9724 * Archive Pitfalls:: Dangers to watch out for when using archives.
9725 * Archive Suffix Rules:: You can write a special kind of suffix rule
9726 for updating archives.
9729 @node Archive Members, Archive Update, Archives, Archives
9730 @section Archive Members as Targets
9731 @cindex archive member targets
9733 An individual member of an archive file can be used as a target or
9734 prerequisite in @code{make}. You specify the member named @var{member} in
9735 archive file @var{archive} as follows:
9738 @var{archive}(@var{member})
9742 This construct is available only in targets and prerequisites, not in
9743 commands! Most programs that you might use in commands do not support this
9744 syntax and cannot act directly on archive members. Only @code{ar} and
9745 other programs specifically designed to operate on archives can do so.
9746 Therefore, valid commands to update an archive member target probably must
9747 use @code{ar}. For example, this rule says to create a member
9748 @file{hack.o} in archive @file{foolib} by copying the file @file{hack.o}:
9751 foolib(hack.o) : hack.o
9755 In fact, nearly all archive member targets are updated in just this way
9756 and there is an implicit rule to do it for you. @strong{Please note:} The
9757 @samp{c} flag to @code{ar} is required if the archive file does not
9760 To specify several members in the same archive, you can write all the
9761 member names together between the parentheses. For example:
9764 foolib(hack.o kludge.o)
9771 foolib(hack.o) foolib(kludge.o)
9774 @cindex wildcard, in archive member
9775 You can also use shell-style wildcards in an archive member reference.
9776 @xref{Wildcards, ,Using Wildcard Characters in File Names}. For
9777 example, @w{@samp{foolib(*.o)}} expands to all existing members of the
9778 @file{foolib} archive whose names end in @samp{.o}; perhaps
9779 @samp{@w{foolib(hack.o)} @w{foolib(kludge.o)}}.
9781 @node Archive Update, Archive Pitfalls, Archive Members, Archives
9782 @section Implicit Rule for Archive Member Targets
9784 Recall that a target that looks like @file{@var{a}(@var{m})} stands for the
9785 member named @var{m} in the archive file @var{a}.
9787 When @code{make} looks for an implicit rule for such a target, as a special
9788 feature it considers implicit rules that match @file{(@var{m})}, as well as
9789 those that match the actual target @file{@var{a}(@var{m})}.
9791 This causes one special rule whose target is @file{(%)} to match. This
9792 rule updates the target @file{@var{a}(@var{m})} by copying the file @var{m}
9793 into the archive. For example, it will update the archive member target
9794 @file{foo.a(bar.o)} by copying the @emph{file} @file{bar.o} into the
9795 archive @file{foo.a} as a @emph{member} named @file{bar.o}.
9797 When this rule is chained with others, the result is very powerful.
9798 Thus, @samp{make "foo.a(bar.o)"} (the quotes are needed to protect the
9799 @samp{(} and @samp{)} from being interpreted specially by the shell) in
9800 the presence of a file @file{bar.c} is enough to cause the following
9801 commands to be run, even without a makefile:
9804 cc -c bar.c -o bar.o
9810 Here @code{make} has envisioned the file @file{bar.o} as an intermediate
9811 file. @xref{Chained Rules, ,Chains of Implicit Rules}.
9813 Implicit rules such as this one are written using the automatic variable
9814 @samp{$%}. @xref{Automatic Variables}.
9816 An archive member name in an archive cannot contain a directory name, but
9817 it may be useful in a makefile to pretend that it does. If you write an
9818 archive member target @file{foo.a(dir/file.o)}, @code{make} will perform
9819 automatic updating with this command:
9822 ar r foo.a dir/file.o
9826 which has the effect of copying the file @file{dir/file.o} into a member
9827 named @file{file.o}. In connection with such usage, the automatic variables
9828 @code{%D} and @code{%F} may be useful.
9831 * Archive Symbols:: How to update archive symbol directories.
9834 @node Archive Symbols, , Archive Update, Archive Update
9835 @subsection Updating Archive Symbol Directories
9836 @cindex @code{__.SYMDEF}
9837 @cindex updating archive symbol directories
9838 @cindex archive symbol directory updating
9839 @cindex symbol directories, updating archive
9840 @cindex directories, updating archive symbol
9842 An archive file that is used as a library usually contains a special member
9843 named @file{__.SYMDEF} that contains a directory of the external symbol
9844 names defined by all the other members. After you update any other
9845 members, you need to update @file{__.SYMDEF} so that it will summarize the
9846 other members properly. This is done by running the @code{ranlib} program:
9849 ranlib @var{archivefile}
9852 Normally you would put this command in the rule for the archive file,
9853 and make all the members of the archive file prerequisites of that rule.
9857 libfoo.a: libfoo.a(x.o) libfoo.a(y.o) @dots{}
9862 The effect of this is to update archive members @file{x.o}, @file{y.o},
9863 etc., and then update the symbol directory member @file{__.SYMDEF} by
9864 running @code{ranlib}. The rules for updating the members are not shown
9865 here; most likely you can omit them and use the implicit rule which copies
9866 files into the archive, as described in the preceding section.
9868 This is not necessary when using the GNU @code{ar} program, which
9869 updates the @file{__.SYMDEF} member automatically.
9871 @node Archive Pitfalls, Archive Suffix Rules, Archive Update, Archives
9872 @section Dangers When Using Archives
9873 @cindex archive, and parallel execution
9874 @cindex parallel execution, and archive update
9875 @cindex archive, and @code{-j}
9876 @cindex @code{-j}, and archive update
9878 It is important to be careful when using parallel execution (the
9879 @code{-j} switch; @pxref{Parallel, ,Parallel Execution}) and archives.
9880 If multiple @code{ar} commands run at the same time on the same archive
9881 file, they will not know about each other and can corrupt the file.
9883 Possibly a future version of @code{make} will provide a mechanism to
9884 circumvent this problem by serializing all commands that operate on the
9885 same archive file. But for the time being, you must either write your
9886 makefiles to avoid this problem in some other way, or not use @code{-j}.
9888 @node Archive Suffix Rules, , Archive Pitfalls, Archives
9889 @section Suffix Rules for Archive Files
9890 @cindex suffix rule, for archive
9891 @cindex archive, suffix rule for
9892 @cindex library archive, suffix rule for
9893 @cindex @code{.a} (archives)
9895 You can write a special kind of suffix rule for dealing with archive
9896 files. @xref{Suffix Rules}, for a full explanation of suffix rules.
9897 Archive suffix rules are obsolete in GNU @code{make}, because pattern
9898 rules for archives are a more general mechanism (@pxref{Archive
9899 Update}). But they are retained for compatibility with other
9902 To write a suffix rule for archives, you simply write a suffix rule
9903 using the target suffix @samp{.a} (the usual suffix for archive files).
9904 For example, here is the old-fashioned suffix rule to update a library
9905 archive from C source files:
9910 $(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $*.o
9917 This works just as if you had written the pattern rule:
9922 $(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $*.o
9928 In fact, this is just what @code{make} does when it sees a suffix rule
9929 with @samp{.a} as the target suffix. Any double-suffix rule
9930 @w{@samp{.@var{x}.a}} is converted to a pattern rule with the target
9931 pattern @samp{(%.o)} and a prerequisite pattern of @samp{%.@var{x}}.
9933 Since you might want to use @samp{.a} as the suffix for some other kind
9934 of file, @code{make} also converts archive suffix rules to pattern rules
9935 in the normal way (@pxref{Suffix Rules}). Thus a double-suffix rule
9936 @w{@samp{.@var{x}.a}} produces two pattern rules: @samp{@w{(%.o):}
9937 @w{%.@var{x}}} and @samp{@w{%.a}: @w{%.@var{x}}}.@refill
9939 @node Features, Missing, Archives, Top
9940 @chapter Features of GNU @code{make}
9941 @cindex features of GNU @code{make}
9943 @cindex compatibility
9945 Here is a summary of the features of GNU @code{make}, for comparison
9946 with and credit to other versions of @code{make}. We consider the
9947 features of @code{make} in 4.2 BSD systems as a baseline. If you are
9948 concerned with writing portable makefiles, you should not use the
9949 features of @code{make} listed here, nor the ones in @ref{Missing}.
9951 Many features come from the version of @code{make} in System V.
9955 The @code{VPATH} variable and its special meaning.
9956 @xref{Directory Search, , Searching Directories for Prerequisites}.
9957 This feature exists in System V @code{make}, but is undocumented.
9958 It is documented in 4.3 BSD @code{make} (which says it mimics System V's
9959 @code{VPATH} feature).@refill
9962 Included makefiles. @xref{Include, ,Including Other Makefiles}.
9963 Allowing multiple files to be included with a single directive is a GNU
9967 Variables are read from and communicated via the environment.
9968 @xref{Environment, ,Variables from the Environment}.
9971 Options passed through the variable @code{MAKEFLAGS} to recursive
9972 invocations of @code{make}.
9973 @xref{Options/Recursion, ,Communicating Options to a Sub-@code{make}}.
9976 The automatic variable @code{$%} is set to the member name
9977 in an archive reference. @xref{Automatic Variables}.
9980 The automatic variables @code{$@@}, @code{$*}, @code{$<}, @code{$%},
9981 and @code{$?} have corresponding forms like @code{$(@@F)} and
9982 @code{$(@@D)}. We have generalized this to @code{$^} as an obvious
9983 extension. @xref{Automatic Variables}.@refill
9986 Substitution variable references.
9987 @xref{Reference, ,Basics of Variable References}.
9990 The command-line options @samp{-b} and @samp{-m}, accepted and
9991 ignored. In System V @code{make}, these options actually do something.
9994 Execution of recursive commands to run @code{make} via the variable
9995 @code{MAKE} even if @samp{-n}, @samp{-q} or @samp{-t} is specified.
9996 @xref{Recursion, ,Recursive Use of @code{make}}.
9999 Support for suffix @samp{.a} in suffix rules. @xref{Archive Suffix
10000 Rules}. This feature is obsolete in GNU @code{make}, because the
10001 general feature of rule chaining (@pxref{Chained Rules, ,Chains of
10002 Implicit Rules}) allows one pattern rule for installing members in an
10003 archive (@pxref{Archive Update}) to be sufficient.
10006 The arrangement of lines and backslash-newline combinations in
10007 commands is retained when the commands are printed, so they appear as
10008 they do in the makefile, except for the stripping of initial
10012 The following features were inspired by various other versions of
10013 @code{make}. In some cases it is unclear exactly which versions inspired
10018 Pattern rules using @samp{%}.
10019 This has been implemented in several versions of @code{make}.
10020 We're not sure who invented it first, but it's been spread around a bit.
10021 @xref{Pattern Rules, ,Defining and Redefining Pattern Rules}.@refill
10024 Rule chaining and implicit intermediate files.
10025 This was implemented by Stu Feldman in his version of @code{make}
10026 for AT&T Eighth Edition Research Unix, and later by Andrew Hume of
10027 AT&T Bell Labs in his @code{mk} program (where he terms it
10028 ``transitive closure''). We do not really know if
10029 we got this from either of them or thought it up ourselves at the
10030 same time. @xref{Chained Rules, ,Chains of Implicit Rules}.
10033 The automatic variable @code{$^} containing a list of all prerequisites
10034 of the current target. We did not invent this, but we have no idea who
10035 did. @xref{Automatic Variables}. The automatic variable
10036 @code{$+} is a simple extension of @code{$^}.
10039 The ``what if'' flag (@samp{-W} in GNU @code{make}) was (as far as we know)
10040 invented by Andrew Hume in @code{mk}.
10041 @xref{Instead of Execution, ,Instead of Executing the Commands}.
10044 The concept of doing several things at once (parallelism) exists in
10045 many incarnations of @code{make} and similar programs, though not in the
10046 System V or BSD implementations. @xref{Execution, ,Command Execution}.
10049 Modified variable references using pattern substitution come from
10050 SunOS 4. @xref{Reference, ,Basics of Variable References}.
10051 This functionality was provided in GNU @code{make} by the
10052 @code{patsubst} function before the alternate syntax was implemented
10053 for compatibility with SunOS 4. It is not altogether clear who
10054 inspired whom, since GNU @code{make} had @code{patsubst} before SunOS
10055 4 was released.@refill
10058 The special significance of @samp{+} characters preceding command lines
10059 (@pxref{Instead of Execution, ,Instead of Executing the Commands}) is
10061 @cite{IEEE Standard 1003.2-1992} (POSIX.2).
10064 The @samp{+=} syntax to append to the value of a variable comes from SunOS
10065 4 @code{make}. @xref{Appending, , Appending More Text to Variables}.
10068 The syntax @w{@samp{@var{archive}(@var{mem1} @var{mem2}@dots{})}} to list
10069 multiple members in a single archive file comes from SunOS 4 @code{make}.
10070 @xref{Archive Members}.
10073 The @code{-include} directive to include makefiles with no error for a
10074 nonexistent file comes from SunOS 4 @code{make}. (But note that SunOS 4
10075 @code{make} does not allow multiple makefiles to be specified in one
10076 @code{-include} directive.) The same feature appears with the name
10077 @code{sinclude} in SGI @code{make} and perhaps others.
10080 The remaining features are inventions new in GNU @code{make}:
10084 Use the @samp{-v} or @samp{--version} option to print version and
10085 copyright information.
10088 Use the @samp{-h} or @samp{--help} option to summarize the options to
10092 Simply-expanded variables. @xref{Flavors, ,The Two Flavors of Variables}.
10095 Pass command-line variable assignments automatically through the
10096 variable @code{MAKE} to recursive @code{make} invocations.
10097 @xref{Recursion, ,Recursive Use of @code{make}}.
10100 Use the @samp{-C} or @samp{--directory} command option to change
10101 directory. @xref{Options Summary, ,Summary of Options}.
10104 Make verbatim variable definitions with @code{define}.
10105 @xref{Defining, ,Defining Variables Verbatim}.
10108 Declare phony targets with the special target @code{.PHONY}.
10110 Andrew Hume of AT&T Bell Labs implemented a similar feature with a
10111 different syntax in his @code{mk} program. This seems to be a case of
10112 parallel discovery. @xref{Phony Targets, ,Phony Targets}.
10115 Manipulate text by calling functions.
10116 @xref{Functions, ,Functions for Transforming Text}.
10119 Use the @samp{-o} or @samp{--old-file}
10120 option to pretend a file's modification-time is old.
10121 @xref{Avoiding Compilation, ,Avoiding Recompilation of Some Files}.
10124 Conditional execution.
10126 This feature has been implemented numerous times in various versions
10127 of @code{make}; it seems a natural extension derived from the features
10128 of the C preprocessor and similar macro languages and is not a
10129 revolutionary concept. @xref{Conditionals, ,Conditional Parts of Makefiles}.
10132 Specify a search path for included makefiles.
10133 @xref{Include, ,Including Other Makefiles}.
10136 Specify extra makefiles to read with an environment variable.
10137 @xref{MAKEFILES Variable, ,The Variable @code{MAKEFILES}}.
10140 Strip leading sequences of @samp{./} from file names, so that
10141 @file{./@var{file}} and @file{@var{file}} are considered to be the
10145 Use a special search method for library prerequisites written in the
10146 form @samp{-l@var{name}}.
10147 @xref{Libraries/Search, ,Directory Search for Link Libraries}.
10150 Allow suffixes for suffix rules
10151 (@pxref{Suffix Rules, ,Old-Fashioned Suffix Rules}) to contain any
10152 characters. In other versions of @code{make}, they must begin with
10153 @samp{.} and not contain any @samp{/} characters.
10156 Keep track of the current level of @code{make} recursion using the
10157 variable @code{MAKELEVEL}. @xref{Recursion, ,Recursive Use of @code{make}}.
10160 Provide any goals given on the command line in the variable
10161 @code{MAKECMDGOALS}. @xref{Goals, ,Arguments to Specify the Goals}.
10164 Specify static pattern rules. @xref{Static Pattern, ,Static Pattern Rules}.
10167 Provide selective @code{vpath} search.
10168 @xref{Directory Search, ,Searching Directories for Prerequisites}.
10171 Provide computed variable references.
10172 @xref{Reference, ,Basics of Variable References}.
10175 Update makefiles. @xref{Remaking Makefiles, ,How Makefiles Are Remade}.
10176 System V @code{make} has a very, very limited form of this
10177 functionality in that it will check out SCCS files for makefiles.
10180 Various new built-in implicit rules.
10181 @xref{Catalogue of Rules, ,Catalogue of Implicit Rules}.
10184 The built-in variable @samp{MAKE_VERSION} gives the version number of
10186 @vindex MAKE_VERSION
10189 @node Missing, Makefile Conventions, Features, Top
10190 @chapter Incompatibilities and Missing Features
10191 @cindex incompatibilities
10192 @cindex missing features
10193 @cindex features, missing
10195 The @code{make} programs in various other systems support a few features
10196 that are not implemented in GNU @code{make}. The POSIX.2 standard
10197 (@cite{IEEE Standard 1003.2-1992}) which specifies @code{make} does not
10198 require any of these features.@refill
10202 A target of the form @samp{@var{file}((@var{entry}))} stands for a member
10203 of archive file @var{file}. The member is chosen, not by name, but by
10204 being an object file which defines the linker symbol @var{entry}.@refill
10206 This feature was not put into GNU @code{make} because of the
10207 nonmodularity of putting knowledge into @code{make} of the internal
10208 format of archive file symbol tables.
10209 @xref{Archive Symbols, ,Updating Archive Symbol Directories}.
10212 Suffixes (used in suffix rules) that end with the character @samp{~}
10213 have a special meaning to System V @code{make};
10214 they refer to the SCCS file that corresponds
10215 to the file one would get without the @samp{~}. For example, the
10216 suffix rule @samp{.c~.o} would make the file @file{@var{n}.o} from
10217 the SCCS file @file{s.@var{n}.c}. For complete coverage, a whole
10218 series of such suffix rules is required.
10219 @xref{Suffix Rules, ,Old-Fashioned Suffix Rules}.
10221 In GNU @code{make}, this entire series of cases is handled by two
10222 pattern rules for extraction from SCCS, in combination with the
10223 general feature of rule chaining.
10224 @xref{Chained Rules, ,Chains of Implicit Rules}.
10227 In System V and 4.3 BSD @code{make}, files found by @code{VPATH} search
10228 (@pxref{Directory Search, ,Searching Directories for Prerequisites}) have their names changed inside command
10229 strings. We feel it is much cleaner to always use automatic variables
10230 and thus make this feature obsolete.@refill
10233 In some Unix @code{make}s, the automatic variable @code{$*} appearing in
10234 the prerequisites of a rule has the amazingly strange ``feature'' of
10235 expanding to the full name of the @emph{target of that rule}. We cannot
10236 imagine what went on in the minds of Unix @code{make} developers to do
10237 this; it is utterly inconsistent with the normal definition of @code{$*}.
10238 @vindex * @r{(automatic variable), unsupported bizarre usage}
10241 In some Unix @code{make}s, implicit rule search
10242 (@pxref{Implicit Rules, ,Using Implicit Rules}) is apparently done for
10243 @emph{all} targets, not just those without commands. This means you can
10254 and Unix @code{make} will intuit that @file{foo.o} depends on
10255 @file{foo.c}.@refill
10257 We feel that such usage is broken. The prerequisite properties of
10258 @code{make} are well-defined (for GNU @code{make}, at least),
10259 and doing such a thing simply does not fit the model.@refill
10262 GNU @code{make} does not include any built-in implicit rules for
10263 compiling or preprocessing EFL programs. If we hear of anyone who is
10264 using EFL, we will gladly add them.
10267 It appears that in SVR4 @code{make}, a suffix rule can be specified with
10268 no commands, and it is treated as if it had empty commands
10269 (@pxref{Empty Commands}). For example:
10276 will override the built-in @file{.c.a} suffix rule.
10278 We feel that it is cleaner for a rule without commands to always simply
10279 add to the prerequisite list for the target. The above example can be
10280 easily rewritten to get the desired behavior in GNU @code{make}:
10287 Some versions of @code{make} invoke the shell with the @samp{-e} flag,
10288 except under @samp{-k} (@pxref{Testing, ,Testing the Compilation of a
10289 Program}). The @samp{-e} flag tells the shell to exit as soon as any
10290 program it runs returns a nonzero status. We feel it is cleaner to
10291 write each shell command line to stand on its own and not require this
10295 @comment The makefile standards are in a separate file that is also
10296 @comment included by standards.texi.
10297 @include make-stds.texi
10299 @node Quick Reference, Error Messages, Makefile Conventions, Top
10300 @appendix Quick Reference
10302 This appendix summarizes the directives, text manipulation functions,
10303 and special variables which GNU @code{make} understands.
10304 @xref{Special Targets}, @ref{Catalogue of Rules, ,Catalogue of Implicit Rules},
10305 and @ref{Options Summary, ,Summary of Options},
10306 for other summaries.
10308 Here is a summary of the directives GNU @code{make} recognizes:
10311 @item define @var{variable}
10314 Define a multi-line, recursively-expanded variable.@*
10317 @item ifdef @var{variable}
10318 @itemx ifndef @var{variable}
10319 @itemx ifeq (@var{a},@var{b})
10320 @itemx ifeq "@var{a}" "@var{b}"
10321 @itemx ifeq '@var{a}' '@var{b}'
10322 @itemx ifneq (@var{a},@var{b})
10323 @itemx ifneq "@var{a}" "@var{b}"
10324 @itemx ifneq '@var{a}' '@var{b}'
10328 Conditionally evaluate part of the makefile.@*
10329 @xref{Conditionals}.
10331 @item include @var{file}
10332 @itemx -include @var{file}
10333 @itemx sinclude @var{file}
10335 Include another makefile.@*
10336 @xref{Include, ,Including Other Makefiles}.
10338 @item override @var{variable} = @var{value}
10339 @itemx override @var{variable} := @var{value}
10340 @itemx override @var{variable} += @var{value}
10341 @itemx override @var{variable} ?= @var{value}
10342 @itemx override define @var{variable}
10345 Define a variable, overriding any previous definition, even one from
10346 the command line.@*
10347 @xref{Override Directive, ,The @code{override} Directive}.
10351 Tell @code{make} to export all variables to child processes by default.@*
10352 @xref{Variables/Recursion, , Communicating Variables to a Sub-@code{make}}.
10354 @item export @var{variable}
10355 @itemx export @var{variable} = @var{value}
10356 @itemx export @var{variable} := @var{value}
10357 @itemx export @var{variable} += @var{value}
10358 @itemx export @var{variable} ?= @var{value}
10359 @itemx unexport @var{variable}
10360 Tell @code{make} whether or not to export a particular variable to child
10362 @xref{Variables/Recursion, , Communicating Variables to a Sub-@code{make}}.
10364 @item vpath @var{pattern} @var{path}
10365 Specify a search path for files matching a @samp{%} pattern.@*
10366 @xref{Selective Search, , The @code{vpath} Directive}.
10368 @item vpath @var{pattern}
10369 Remove all search paths previously specified for @var{pattern}.
10372 Remove all search paths previously specified in any @code{vpath}
10376 Here is a summary of the built-in functions (@pxref{Functions}):
10379 @item $(subst @var{from},@var{to},@var{text})
10380 Replace @var{from} with @var{to} in @var{text}.@*
10381 @xref{Text Functions, , Functions for String Substitution and Analysis}.
10383 @item $(patsubst @var{pattern},@var{replacement},@var{text})
10384 Replace words matching @var{pattern} with @var{replacement} in @var{text}.@*
10385 @xref{Text Functions, , Functions for String Substitution and Analysis}.
10387 @item $(strip @var{string})
10388 Remove excess whitespace characters from @var{string}.@*
10389 @xref{Text Functions, , Functions for String Substitution and Analysis}.
10391 @item $(findstring @var{find},@var{text})
10392 Locate @var{find} in @var{text}.@*
10393 @xref{Text Functions, , Functions for String Substitution and Analysis}.
10395 @item $(filter @var{pattern}@dots{},@var{text})
10396 Select words in @var{text} that match one of the @var{pattern} words.@*
10397 @xref{Text Functions, , Functions for String Substitution and Analysis}.
10399 @item $(filter-out @var{pattern}@dots{},@var{text})
10400 Select words in @var{text} that @emph{do not} match any of the @var{pattern} words.@*
10401 @xref{Text Functions, , Functions for String Substitution and Analysis}.
10403 @item $(sort @var{list})
10404 Sort the words in @var{list} lexicographically, removing duplicates.@*
10405 @xref{Text Functions, , Functions for String Substitution and Analysis}.
10407 @item $(word @var{n},@var{text})
10408 Extract the @var{n}th word (one-origin) of @var{text}.@*
10409 @xref{Text Functions, , Functions for String Substitution and Analysis}.
10411 @item $(words @var{text})
10412 Count the number of words in @var{text}.@*
10413 @xref{Text Functions, , Functions for String Substitution and Analysis}.
10415 @item $(wordlist @var{s},@var{e},@var{text})
10416 Returns the list of words in @var{text} from @var{s} to @var{e}.@*
10417 @xref{Text Functions, , Functions for String Substitution and Analysis}.
10419 @item $(firstword @var{names}@dots{})
10420 Extract the first word of @var{names}.@*
10421 @xref{Text Functions, , Functions for String Substitution and Analysis}.
10423 @item $(lastword @var{names}@dots{})
10424 Extract the last word of @var{names}.@*
10425 @xref{Text Functions, , Functions for String Substitution and Analysis}.
10427 @item $(dir @var{names}@dots{})
10428 Extract the directory part of each file name.@*
10429 @xref{File Name Functions, ,Functions for File Names}.
10431 @item $(notdir @var{names}@dots{})
10432 Extract the non-directory part of each file name.@*
10433 @xref{File Name Functions, ,Functions for File Names}.
10435 @item $(suffix @var{names}@dots{})
10436 Extract the suffix (the last @samp{.} and following characters) of each file name.@*
10437 @xref{File Name Functions, ,Functions for File Names}.
10439 @item $(basename @var{names}@dots{})
10440 Extract the base name (name without suffix) of each file name.@*
10441 @xref{File Name Functions, ,Functions for File Names}.
10443 @item $(addsuffix @var{suffix},@var{names}@dots{})
10444 Append @var{suffix} to each word in @var{names}.@*
10445 @xref{File Name Functions, ,Functions for File Names}.
10447 @item $(addprefix @var{prefix},@var{names}@dots{})
10448 Prepend @var{prefix} to each word in @var{names}.@*
10449 @xref{File Name Functions, ,Functions for File Names}.
10451 @item $(join @var{list1},@var{list2})
10452 Join two parallel lists of words.@*
10453 @xref{File Name Functions, ,Functions for File Names}.
10455 @item $(wildcard @var{pattern}@dots{})
10456 Find file names matching a shell file name pattern (@emph{not} a
10457 @samp{%} pattern).@*
10458 @xref{Wildcard Function, ,The Function @code{wildcard}}.
10460 @item $(realpath @var{names}@dots{})
10461 For each file name in @var{names}, expand to an absolute name that
10462 does not contain any @code{.}, @code{..}, nor symlinks.@*
10463 @xref{File Name Functions, ,Functions for File Names}.
10465 @item $(abspath @var{names}@dots{})
10466 For each file name in @var{names}, expand to an absolute name that
10467 does not contain any @code{.} or @code{..} components, but preserves
10469 @xref{File Name Functions, ,Functions for File Names}.
10471 @item $(error @var{text}@dots{})
10473 When this function is evaluated, @code{make} generates a fatal error
10474 with the message @var{text}.@*
10475 @xref{Make Control Functions, ,Functions That Control Make}.
10477 @item $(warning @var{text}@dots{})
10479 When this function is evaluated, @code{make} generates a warning with
10480 the message @var{text}.@*
10481 @xref{Make Control Functions, ,Functions That Control Make}.
10483 @item $(shell @var{command})
10485 Execute a shell command and return its output.@*
10486 @xref{Shell Function, , The @code{shell} Function}.
10488 @item $(origin @var{variable})
10490 Return a string describing how the @code{make} variable @var{variable} was
10492 @xref{Origin Function, , The @code{origin} Function}.
10494 @item $(flavor @var{variable})
10496 Return a string describing the flavor of the @code{make} variable
10498 @xref{Flavor Function, , The @code{flavor} Function}.
10500 @item $(foreach @var{var},@var{words},@var{text})
10502 Evaluate @var{text} with @var{var} bound to each word in @var{words},
10503 and concatenate the results.@*
10504 @xref{Foreach Function, ,The @code{foreach} Function}.
10506 @item $(call @var{var},@var{param},@dots{})
10508 Evaluate the variable @var{var} replacing any references to @code{$(1)},
10509 @code{$(2)} with the first, second, etc.@: @var{param} values.@*
10510 @xref{Call Function, ,The @code{call} Function}.
10512 @item $(eval @var{text})
10514 Evaluate @var{text} then read the results as makefile commands.
10515 Expands to the empty string.@*
10516 @xref{Eval Function, ,The @code{eval} Function}.
10518 @item $(value @var{var})
10520 Evaluates to the contents of the variable @var{var}, with no expansion
10522 @xref{Value Function, ,The @code{value} Function}.
10525 Here is a summary of the automatic variables.
10526 @xref{Automatic Variables},
10527 for full information.
10531 The file name of the target.
10534 The target member name, when the target is an archive member.
10537 The name of the first prerequisite.
10540 The names of all the prerequisites that are
10541 newer than the target, with spaces between them.
10542 For prerequisites which are archive members, only
10543 the member named is used (@pxref{Archives}).
10547 The names of all the prerequisites, with spaces between them. For
10548 prerequisites which are archive members, only the member named is used
10549 (@pxref{Archives}). The value of @code{$^} omits duplicate
10550 prerequisites, while @code{$+} retains them and preserves their order.
10553 The stem with which an implicit rule matches
10554 (@pxref{Pattern Match, ,How Patterns Match}).
10558 The directory part and the file-within-directory part of @code{$@@}.
10562 The directory part and the file-within-directory part of @code{$*}.
10566 The directory part and the file-within-directory part of @code{$%}.
10570 The directory part and the file-within-directory part of @code{$<}.
10574 The directory part and the file-within-directory part of @code{$^}.
10578 The directory part and the file-within-directory part of @code{$+}.
10582 The directory part and the file-within-directory part of @code{$?}.
10585 These variables are used specially by GNU @code{make}:
10590 Makefiles to be read on every invocation of @code{make}.@*
10591 @xref{MAKEFILES Variable, ,The Variable @code{MAKEFILES}}.
10595 Directory search path for files not found in the current directory.@*
10596 @xref{General Search, , @code{VPATH} Search Path for All Prerequisites}.
10600 The name of the system default command interpreter, usually @file{/bin/sh}.
10601 You can set @code{SHELL} in the makefile to change the shell used to run
10602 commands. @xref{Execution, ,Command Execution}. The @code{SHELL}
10603 variable is handled specially when importing from and exporting to the
10604 environment. @xref{Choosing the Shell}.
10608 On MS-DOS only, the name of the command interpreter that is to be used
10609 by @code{make}. This value takes precedence over the value of
10610 @code{SHELL}. @xref{Execution, ,MAKESHELL variable}.
10614 The name with which @code{make} was invoked.
10615 Using this variable in commands has special meaning.
10616 @xref{MAKE Variable, ,How the @code{MAKE} Variable Works}.
10620 The number of levels of recursion (sub-@code{make}s).@*
10621 @xref{Variables/Recursion}.
10625 The flags given to @code{make}. You can set this in the environment or
10626 a makefile to set flags.@*
10627 @xref{Options/Recursion, ,Communicating Options to a Sub-@code{make}}.
10629 It is @emph{never} appropriate to use @code{MAKEFLAGS} directly on a
10630 command line: its contents may not be quoted correctly for use in the
10631 shell. Always allow recursive @code{make}'s to obtain these values
10632 through the environment from its parent.
10636 The targets given to @code{make} on the command line. Setting this
10637 variable has no effect on the operation of @code{make}.@*
10638 @xref{Goals, ,Arguments to Specify the Goals}.
10642 Set to the pathname of the current working directory (after all
10643 @code{-C} options are processed, if any). Setting this variable has no
10644 effect on the operation of @code{make}.@*
10645 @xref{Recursion, ,Recursive Use of @code{make}}.
10649 The default list of suffixes before @code{make} reads any makefiles.
10652 Defines the naming of the libraries @code{make} searches for, and their
10654 @xref{Libraries/Search, ,Directory Search for Link Libraries}.
10657 @node Error Messages, Complex Makefile, Quick Reference, Top
10658 @comment node-name, next, previous, up
10659 @appendix Errors Generated by Make
10661 Here is a list of the more common errors you might see generated by
10662 @code{make}, and some information about what they mean and how to fix
10665 Sometimes @code{make} errors are not fatal, especially in the presence
10666 of a @code{-} prefix on a command script line, or the @code{-k} command
10667 line option. Errors that are fatal are prefixed with the string
10670 Error messages are all either prefixed with the name of the program
10671 (usually @samp{make}), or, if the error is found in a makefile, the name
10672 of the file and linenumber containing the problem.
10674 In the table below, these common prefixes are left off.
10678 @item [@var{foo}] Error @var{NN}
10679 @itemx [@var{foo}] @var{signal description}
10680 These errors are not really @code{make} errors at all. They mean that a
10681 program that @code{make} invoked as part of a command script returned a
10682 non-0 error code (@samp{Error @var{NN}}), which @code{make} interprets
10683 as failure, or it exited in some other abnormal fashion (with a
10684 signal of some type). @xref{Errors, ,Errors in Commands}.
10686 If no @code{***} is attached to the message, then the subprocess failed
10687 but the rule in the makefile was prefixed with the @code{-} special
10688 character, so @code{make} ignored the error.
10690 @item missing separator. Stop.
10691 @itemx missing separator (did you mean TAB instead of 8 spaces?). Stop.
10692 This means that @code{make} could not understand much of anything about
10693 the command line it just read. GNU @code{make} looks for various kinds
10694 of separators (@code{:}, @code{=}, TAB characters, etc.) to help it
10695 decide what kind of commandline it's seeing. This means it couldn't
10698 One of the most common reasons for this message is that you (or perhaps
10699 your oh-so-helpful editor, as is the case with many MS-Windows editors)
10700 have attempted to indent your command scripts with spaces instead of a
10701 TAB character. In this case, @code{make} will use the second form of
10702 the error above. Remember that every line in the command script must
10703 begin with a TAB character. Eight spaces do not count. @xref{Rule
10706 @item commands commence before first target. Stop.
10707 @itemx missing rule before commands. Stop.
10708 This means the first thing in the makefile seems to be part of a command
10709 script: it begins with a TAB character and doesn't appear to be a legal
10710 @code{make} command (such as a variable assignment). Command scripts
10711 must always be associated with a target.
10713 The second form is generated if the line has a semicolon as the first
10714 non-whitespace character; @code{make} interprets this to mean you left
10715 out the "target: prerequisite" section of a rule. @xref{Rule Syntax}.
10717 @item No rule to make target `@var{xxx}'.
10718 @itemx No rule to make target `@var{xxx}', needed by `@var{yyy}'.
10719 This means that @code{make} decided it needed to build a target, but
10720 then couldn't find any instructions in the makefile on how to do that,
10721 either explicit or implicit (including in the default rules database).
10723 If you want that file to be built, you will need to add a rule to your
10724 makefile describing how that target can be built. Other possible
10725 sources of this problem are typos in the makefile (if that filename is
10726 wrong) or a corrupted source tree (if that file is not supposed to be
10727 built, but rather only a prerequisite).
10729 @item No targets specified and no makefile found. Stop.
10730 @itemx No targets. Stop.
10731 The former means that you didn't provide any targets to be built on the
10732 command line, and @code{make} couldn't find any makefiles to read in.
10733 The latter means that some makefile was found, but it didn't contain any
10734 default goal and none was given on the command line. GNU @code{make}
10735 has nothing to do in these situations.
10736 @xref{Makefile Arguments, ,Arguments to Specify the Makefile}.@refill
10738 @item Makefile `@var{xxx}' was not found.
10739 @itemx Included makefile `@var{xxx}' was not found.
10740 A makefile specified on the command line (first form) or included
10741 (second form) was not found.
10743 @item warning: overriding commands for target `@var{xxx}'
10744 @itemx warning: ignoring old commands for target `@var{xxx}'
10745 GNU @code{make} allows commands to be specified only once per target
10746 (except for double-colon rules). If you give commands for a target
10747 which already has been defined to have commands, this warning is issued
10748 and the second set of commands will overwrite the first set.
10749 @xref{Multiple Rules, ,Multiple Rules for One Target}.
10751 @item Circular @var{xxx} <- @var{yyy} dependency dropped.
10752 This means that @code{make} detected a loop in the dependency graph:
10753 after tracing the prerequisite @var{yyy} of target @var{xxx}, and its
10754 prerequisites, etc., one of them depended on @var{xxx} again.
10756 @item Recursive variable `@var{xxx}' references itself (eventually). Stop.
10757 This means you've defined a normal (recursive) @code{make} variable
10758 @var{xxx} that, when it's expanded, will refer to itself (@var{xxx}).
10759 This is not allowed; either use simply-expanded variables (@code{:=}) or
10760 use the append operator (@code{+=}). @xref{Using Variables, ,How to Use
10763 @item Unterminated variable reference. Stop.
10764 This means you forgot to provide the proper closing parenthesis
10765 or brace in your variable or function reference.
10767 @item insufficient arguments to function `@var{xxx}'. Stop.
10768 This means you haven't provided the requisite number of arguments for
10769 this function. See the documentation of the function for a description
10770 of its arguments. @xref{Functions, ,Functions for Transforming Text}.
10772 @item missing target pattern. Stop.
10773 @itemx multiple target patterns. Stop.
10774 @itemx target pattern contains no `%'. Stop.
10775 @itemx mixed implicit and static pattern rules. Stop.
10776 These are generated for malformed static pattern rules. The first means
10777 there's no pattern in the target section of the rule; the second means
10778 there are multiple patterns in the target section; the third means
10779 the target doesn't contain a pattern character (@code{%}); and the
10780 fourth means that all three parts of the static pattern rule contain
10781 pattern characters (@code{%})--only the first two parts should.
10782 @xref{Static Usage, ,Syntax of Static Pattern Rules}.
10784 @item warning: -jN forced in submake: disabling jobserver mode.
10785 This warning and the next are generated if @code{make} detects error
10786 conditions related to parallel processing on systems where
10787 sub-@code{make}s can communicate (@pxref{Options/Recursion,
10788 ,Communicating Options to a Sub-@code{make}}). This warning is
10789 generated if a recursive invocation of a @code{make} process is forced
10790 to have @samp{-j@var{N}} in its argument list (where @var{N} is greater
10791 than one). This could happen, for example, if you set the @code{MAKE}
10792 environment variable to @samp{make -j2}. In this case, the
10793 sub-@code{make} doesn't communicate with other @code{make} processes and
10794 will simply pretend it has two jobs of its own.
10796 @item warning: jobserver unavailable: using -j1. Add `+' to parent make rule.
10797 In order for @code{make} processes to communicate, the parent will pass
10798 information to the child. Since this could result in problems if the
10799 child process isn't actually a @code{make}, the parent will only do this
10800 if it thinks the child is a @code{make}. The parent uses the normal
10801 algorithms to determine this (@pxref{MAKE Variable, ,How the @code{MAKE}
10802 Variable Works}). If the makefile is constructed such that the parent
10803 doesn't know the child is a @code{make} process, then the child will
10804 receive only part of the information necessary. In this case, the child
10805 will generate this warning message and proceed with its build in a
10810 @node Complex Makefile, GNU Free Documentation License, Error Messages, Top
10811 @appendix Complex Makefile Example
10813 Here is the makefile for the GNU @code{tar} program. This is a
10814 moderately complex makefile.
10816 Because it is the first target, the default goal is @samp{all}. An
10817 interesting feature of this makefile is that @file{testpad.h} is a
10818 source file automatically created by the @code{testpad} program,
10819 itself compiled from @file{testpad.c}.
10821 If you type @samp{make} or @samp{make all}, then @code{make} creates
10822 the @file{tar} executable, the @file{rmt} daemon that provides
10823 remote tape access, and the @file{tar.info} Info file.
10825 If you type @samp{make install}, then @code{make} not only creates
10826 @file{tar}, @file{rmt}, and @file{tar.info}, but also installs
10829 If you type @samp{make clean}, then @code{make} removes the @samp{.o}
10830 files, and the @file{tar}, @file{rmt}, @file{testpad},
10831 @file{testpad.h}, and @file{core} files.
10833 If you type @samp{make distclean}, then @code{make} not only removes
10834 the same files as does @samp{make clean} but also the
10835 @file{TAGS}, @file{Makefile}, and @file{config.status} files.
10836 (Although it is not evident, this makefile (and
10837 @file{config.status}) is generated by the user with the
10838 @code{configure} program, which is provided in the @code{tar}
10839 distribution, but is not shown here.)
10841 If you type @samp{make realclean}, then @code{make} removes the same
10842 files as does @samp{make distclean} and also removes the Info files
10843 generated from @file{tar.texinfo}.
10845 In addition, there are targets @code{shar} and @code{dist} that create
10850 # Generated automatically from Makefile.in by configure.
10851 # Un*x Makefile for GNU tar program.
10852 # Copyright (C) 1991 Free Software Foundation, Inc.
10856 # This program is free software; you can redistribute
10857 # it and/or modify it under the terms of the GNU
10858 # General Public License @dots{}
10865 #### Start of system configuration section. ####
10870 # If you use gcc, you should either run the
10871 # fixincludes script that comes with it or else use
10872 # gcc with the -traditional option. Otherwise ioctl
10873 # calls will be compiled incorrectly on some systems.
10876 INSTALL = /usr/local/bin/install -c
10877 INSTALLDATA = /usr/local/bin/install -c -m 644
10880 # Things you might add to DEFS:
10881 # -DSTDC_HEADERS If you have ANSI C headers and
10883 # -DPOSIX If you have POSIX.1 headers and
10885 # -DBSD42 If you have sys/dir.h (unless
10886 # you use -DPOSIX), sys/file.h,
10887 # and st_blocks in `struct stat'.
10888 # -DUSG If you have System V/ANSI C
10889 # string and memory functions
10890 # and headers, sys/sysmacros.h,
10891 # fcntl.h, getcwd, no valloc,
10892 # and ndir.h (unless
10893 # you use -DDIRENT).
10894 # -DNO_MEMORY_H If USG or STDC_HEADERS but do not
10895 # include memory.h.
10896 # -DDIRENT If USG and you have dirent.h
10897 # instead of ndir.h.
10898 # -DSIGTYPE=int If your signal handlers
10899 # return int, not void.
10900 # -DNO_MTIO If you lack sys/mtio.h
10901 # (magtape ioctls).
10902 # -DNO_REMOTE If you do not have a remote shell
10904 # -DUSE_REXEC To use rexec for remote tape
10905 # operations instead of
10906 # forking rsh or remsh.
10907 # -DVPRINTF_MISSING If you lack vprintf function
10908 # (but have _doprnt).
10909 # -DDOPRNT_MISSING If you lack _doprnt function.
10910 # Also need to define
10911 # -DVPRINTF_MISSING.
10912 # -DFTIME_MISSING If you lack ftime system call.
10913 # -DSTRSTR_MISSING If you lack strstr function.
10914 # -DVALLOC_MISSING If you lack valloc function.
10915 # -DMKDIR_MISSING If you lack mkdir and
10916 # rmdir system calls.
10917 # -DRENAME_MISSING If you lack rename system call.
10918 # -DFTRUNCATE_MISSING If you lack ftruncate
10920 # -DV7 On Version 7 Unix (not
10921 # tested in a long time).
10922 # -DEMUL_OPEN3 If you lack a 3-argument version
10923 # of open, and want to emulate it
10924 # with system calls you do have.
10925 # -DNO_OPEN3 If you lack the 3-argument open
10926 # and want to disable the tar -k
10927 # option instead of emulating open.
10928 # -DXENIX If you have sys/inode.h
10929 # and need it 94 to be included.
10931 DEFS = -DSIGTYPE=int -DDIRENT -DSTRSTR_MISSING \
10932 -DVPRINTF_MISSING -DBSD42
10933 # Set this to rtapelib.o unless you defined NO_REMOTE,
10934 # in which case make it empty.
10935 RTAPELIB = rtapelib.o
10937 DEF_AR_FILE = /dev/rmt8
10942 CFLAGS = $(CDEBUG) -I. -I$(srcdir) $(DEFS) \
10943 -DDEF_AR_FILE=\"$(DEF_AR_FILE)\" \
10944 -DDEFBLOCKING=$(DEFBLOCKING)
10949 prefix = /usr/local
10950 # Prefix for each installed program,
10951 # normally empty or `g'.
10954 # The directory to install tar in.
10955 bindir = $(prefix)/bin
10957 # The directory to install the info files in.
10958 infodir = $(prefix)/info
10961 #### End of system configuration section. ####
10963 SRC1 = tar.c create.c extract.c buffer.c \
10964 getoldopt.c update.c gnu.c mangle.c
10965 SRC2 = version.c list.c names.c diffarch.c \
10966 port.c wildmat.c getopt.c
10967 SRC3 = getopt1.c regex.c getdate.y
10968 SRCS = $(SRC1) $(SRC2) $(SRC3)
10969 OBJ1 = tar.o create.o extract.o buffer.o \
10970 getoldopt.o update.o gnu.o mangle.o
10971 OBJ2 = version.o list.o names.o diffarch.o \
10972 port.o wildmat.o getopt.o
10973 OBJ3 = getopt1.o regex.o getdate.o $(RTAPELIB)
10974 OBJS = $(OBJ1) $(OBJ2) $(OBJ3)
10976 AUX = README COPYING ChangeLog Makefile.in \
10977 makefile.pc configure configure.in \
10978 tar.texinfo tar.info* texinfo.tex \
10979 tar.h port.h open3.h getopt.h regex.h \
10980 rmt.h rmt.c rtapelib.c alloca.c \
10981 msd_dir.h msd_dir.c tcexparg.c \
10982 level-0 level-1 backup-specs testpad.c
10986 all: tar rmt tar.info
10991 $(CC) $(LDFLAGS) -o $@@ $(OBJS) $(LIBS)
10996 $(CC) $(CFLAGS) $(LDFLAGS) -o $@@ rmt.c
11000 tar.info: tar.texinfo
11001 makeinfo tar.texinfo
11007 $(INSTALL) tar $(bindir)/$(binprefix)tar
11008 -test ! -f rmt || $(INSTALL) rmt /etc/rmt
11009 $(INSTALLDATA) $(srcdir)/tar.info* $(infodir)
11013 $(OBJS): tar.h port.h testpad.h
11014 regex.o buffer.o tar.o: regex.h
11015 # getdate.y has 8 shift/reduce conflicts.
11025 $(CC) -o $@@ testpad.o
11036 rm -f *.o tar rmt testpad testpad.h core
11042 rm -f TAGS Makefile config.status
11047 realclean: distclean
11053 shar: $(SRCS) $(AUX)
11054 shar $(SRCS) $(AUX) | compress \
11055 > tar-`sed -e '/version_string/!d' \
11056 -e 's/[^0-9.]*\([0-9.]*\).*/\1/' \
11063 dist: $(SRCS) $(AUX)
11065 -e '/version_string/!d' \
11066 -e 's/[^0-9.]*\([0-9.]*\).*/\1/' \
11068 version.c` > .fname
11069 -rm -rf `cat .fname`
11071 ln $(SRCS) $(AUX) `cat .fname`
11072 tar chZf `cat .fname`.tar.Z `cat .fname`
11073 -rm -rf `cat .fname` .fname
11077 tar.zoo: $(SRCS) $(AUX)
11081 for X in $(SRCS) $(AUX) ; do \
11083 sed 's/$$/^M/' $$X \
11084 > tmp.dir/$$X ; done
11085 cd tmp.dir ; zoo aM ../tar.zoo *
11094 @node Concept Index, Name Index, GNU Free Documentation License, Top
11095 @unnumbered Index of Concepts
11099 @node Name Index, , Concept Index, Top
11100 @unnumbered Index of Functions, Variables, & Directives