(target_environment): Don't use shell_var if its `value' field is NULL.

[make.git] / README.DOS.template

Port of GNU Make to 32-bit protected mode on MSDOS and MS-Windows.

Builds with DJGPP v2 port of GNU C/C++ compiler and utilities.


New (since 3.74) DOS-specific features:

   1. Supports long filenames when run from DOS box on Windows 9x.

   2. Supports both stock DOS COMMAND.COM and Unix-style shells
      (details in ``Notes'' below).

   3. Supports DOS drive letters in dependencies and pattern rules.

   4. Better support for DOS-style backslashes in pathnames (but see
      ``Notes'' below).

   5. The $(shell) built-in can run arbitrary complex commands,
      including pipes and redirection, even when COMMAND.COM is your
      shell.

   6. Can be built without floating-point code (see below).

   7. Supports signals in child programs and restores the original
      directory if the child was interrupted.

   8. Can be built without (a previous version of) Make.

   9. The build process requires only standard tools.  (Optional
      targets like "install:" and "clean:" still need additional
      programs, though, see below.)

  10. Beginning with v3.78, the test suite works in the DJGPP
      environment (requires Perl and auxiliary tools; see below).


To install a binary distribution:

   Simply unzip the makNNNb.zip file (where NNN is the version number)
   preserving the directory structure (-d switch if you use PKUNZIP).
   If you are installing Make on Windows 9X or Windows 2000, use an
   unzip program that supports long filenames in zip files.  After
   unzipping, make sure the directory with make.exe is on your PATH,
   and that's all you need to use Make.


To build from sources:

   1. Unzip the archive, preserving the directory structure (-d switch
      if you use PKUNZIP).  If you build Make on Windows 9X or Windows
      2000, use an unzip program that supports long filenames in zip
      files.

      If you are unpacking an official GNU source distribution, use
      either DJTAR (which is part of the DJGPP development
      environment), or the DJGPP port of GNU Tar.

   2. Invoke the `configure.bat' batch file.

      If you are building Make in-place, i.e. in the same directory
      where its sources are kept, just type "configure.bat" and press
      [Enter].  Otherwise, you need to supply the path to the source
      directory as an argument to the batch file, like this:

        c:\djgpp\gnu\make-%VERSION%\configure.bat c:/djgpp/gnu/make-%VERSION%

      Note the forward slashes in the source path argument: you MUST
      use them here.

   3. If configure.bat doesn't find a working Make, it will suggest to
      use the `dosbuild.bat' batch file to build Make.  Either do as it
      suggests or install another Make program (a pre-compiled binary
      should be available from the usual DJGPP sites) and rerun
      configure.bat.

   4. If you will need to run Make on machines without an FPU, you
      might consider building a version of Make which doesn't issue
      floating-point instructions (they don't help much on MSDOS
      anyway).  To this end, edit the Makefile created by
      configure.bat and add -DNO_FLOAT to the value of CPPFLAGS.

   5. Invoke Make.

      If you are building from outside of the source directory, you
      need to tell Make where the sources are, like this:

                make srcdir=c:/djgpp/gnu/make-%VERSION%

      (configure.bat will tell you this when it finishes).  You MUST
      use a full, not relative, name of the source directory here, or
      else Make might fail.

   6. After Make finishes, if you have a Unix-style shell installed,
      you can use the `install' target to install the package.  You
      will also need GNU Fileutils and GNU Sed for this (they should
      be available from the DJGPP sites).

      By default, GNU make will install into your DJGPP installation
      area.  If you wish to use a different directory, override the
      DESTDIR variable when invoking "make install", like this:

                make install DESTDIR=c:/other/dir

      This causes the make executable to be placed in c:/other/dir/bin,
      the man pages in c:/other/dir/man, etc.

      Without a Unix-style shell, you will have to install programs
      and the docs manually.  Copy make.exe to a directory on your
      PATH, make.i* info files to your Info directory, and update the
      file `dir' in your Info directory by adding the following item
      to the main menu:

        * Make: (make.info).           The GNU make utility.

      If you have the `install-info' program (from the GNU Texinfo
      package), it will do that for you if you invoke it like this:

        install-info --info-dir=c:/djgpp/info c:/djgpp/info/make.info

      (If your Info directory is other than C:\DJGPP\INFO, change this
      command accordingly.)

   7. The `clean' targets also require Unix-style shell, and GNU Sed
      and `rm' programs (the latter from Fileutils).

   8. To run the test suite, type "make check".  This requires a Unix
      shell (I used the DJGPP port of Bash 2.03), Perl, Sed, Fileutils
      and Sh-utils.


Notes:
-----

   1. The shell issue.

      This is probably the most significant improvement, first
      introduced in the port of GNU Make 3.75.

      The original behavior of GNU Make is to invoke commands
      directly, as long as they don't include characters special to
      the shell or internal shell commands, because that is faster.
      When shell features like redirection or filename wildcards are
      involved, Make calls the shell.

      This port supports both DOS shells (the stock COMMAND.COM and its
      4DOS/NDOS replacements), and Unix-style shells (tested with the
      venerable Stewartson's `ms_sh' 2.3 and the DJGPP port of `bash' by
      Daisuke Aoyama <jack@st.rim.or.jp>).

      When the $SHELL variable points to a Unix-style shell, Make
      works just like you'd expect on Unix, calling the shell for any
      command that involves characters special to the shell or
      internal shell commands.  The only difference is that, since
      there is no standard way to pass command lines longer than the
      infamous DOS 126-character limit, this port of Make writes the
      command line to a temporary disk file and then invokes the shell
      on that file.

      If $SHELL points to a DOS-style shell, however, Make will not
      call it automatically, as it does with Unix shells.  Stock
      COMMAND.COM is too dumb and would unnecessarily limit the
      functionality of Make.  For example, you would not be able to
      use long command lines in commands that use redirection or
      pipes.  Therefore, when presented with a DOS shell, this port of
      Make will emulate most of the shell functionality, like
      redirection and pipes, and shall only call the shell when a
      batch file or a command internal to the shell is invoked.  (Even
      when a command is an internal shell command, Make will first
      search the $PATH for it, so that if a Makefile calls `mkdir',
      you can install, say, a port of GNU `mkdir' and have it called
      in that case.)

      The key to all this is the extended functionality of `spawn' and
      `system' functions from the DJGPP library; this port just calls
      `system' where it would invoke the shell on Unix.  The most
      important aspect of these functions is that they use a special
      mechanism to pass long (up to 16KB) command lines to DJGPP
      programs.  In addition, `system' emulates some internal
      commands, like `cd' (so that you can now use forward slashes
      with it, and can also change the drive if the directory is on
      another drive).  Another aspect worth mentioning is that you can
      call Unix shell scripts directly, provided that the shell whose
      name is mentioned on the first line of the script is installed
      anywhere along the $PATH.  It is impossible to tell here
      everything about these functions; refer to the DJGPP library
      reference for more details.

      The $(shell) built-in is implemented in this port by calling
      `popen'.  Since `popen' calls `system', the above considerations
      are valid for $(shell) as well.  In particular, you can put
      arbitrary complex commands, including pipes and redirection,
      inside $(shell), which is in many cases a valid substitute for
      the Unix-style command substitution (`command`) feature.


   2. "SHELL=/bin/sh" -- or is it?

      Many Unix Makefiles include a line which sets the SHELL, for
      those versions of Make which don't have this as the default.
      Since many DOS systems don't have `sh' installed (in fact, most
      of them don't even have a `/bin' directory), this port takes
      such directives with a grain of salt.  It will only honor such a
      directive if the basename of the shell name (like `sh' in the
      above example) can indeed be found in the directory that is
      mentioned in the SHELL= line (`/bin' in the above example), or
      in the current working directory, or anywhere on the $PATH (in
      that order).  If the basename doesn't include a filename
      extension, Make will look for any known extension that indicates
      an executable file (.exe, .com, .bat, .btm, .sh, and even .sed
      and .pl).  If any such file is found, then $SHELL will be
      defined to the exact pathname of that file, and that shell will
      hence be used for the rest of processing.  But if the named
      shell is *not* found, the line which sets it will be effectively
      ignored, leaving the value of $SHELL as it was before.  Since a
      lot of decisions that this port makes depend on the gender of
      the shell, I feel it doesn't make any sense to tailor Make's
      behavior to a shell which is nowhere to be found.

      Note that the above special handling of "SHELL=" only happens
      for Makefiles; if you set $SHELL in the environment or on the
      Make command line, you are expected to give the complete
      pathname of the shell, including the filename extension.

      The default value of $SHELL is computed as on Unix (see the Make
      manual for details), except that if $SHELL is not defined in the
      environment, $COMSPEC is used.  Also, if an environment variable
      named $MAKESHELL is defined, it takes precedence over both
      $COMSPEC and $SHELL.  Note that, unlike Unix, $SHELL in the
      environment *is* used to set the shell (since on MSDOS, it's
      unlikely that the interactive shell will not be suitable for
      Makefile processing).

      The bottom line is that you can now write Makefiles where some
      of the targets require a real (i.e. Unix-like) shell, which will
      nevertheless work when such shell is not available (provided, of
      course, that the commands which should always work, don't
      require such a shell).  More important, you can convert Unix
      Makefiles to MSDOS and leave the line which sets the shell
      intact, so that people who do have Unixy shell could use it for
      targets which aren't converted to DOS (like `install' and
      `uninstall', for example).


   3. Default directories.

      GNU Make knows about standard directories where it searches for
      library and include files mentioned in the Makefile.  Since
      MSDOS machines don't have standard places for these, this port
      will search ${DJDIR}/lib and ${DJDIR}/include respectively.
      $DJDIR is defined automatically by the DJGPP startup code as the
      root of the DJGPP installation tree (unless you've tampered with
      the DJGPP.ENV file).  This should provide reasonable default
      values, unless you moved parts of DJGPP to other directories.


   4. Letter-case in filenames.

      If you run Make on Windows 9x, you should be aware of the
      letter-case issue.  Make is internally case-sensitive, but all
      file operations are case-insensitive on Windows 9x, so
      e.g. files `FAQ', `faq' and `Faq' all refer to the same file, as
      far as Windows is concerned.  The underlying DJGPP C library
      functions honor the letter-case of the filenames they get from
      the OS, except that by default, they down-case 8+3 DOS filenames
      which are stored in upper case in the directory and would break
      many Makefiles otherwise.  (The details of which filenames are
      converted to lower case are explained in the DJGPP libc docs,
      under the `_preserve_fncase' and `_lfn_gen_short_fname'
      functions, but as a thumb rule, any filename that is stored in
      upper case in the directory, is a valid DOS 8+3 filename and
      doesn't include characters invalid on MSDOS FAT filesystems,
      will be automatically down-cased.)  User reports that I have
      indicate that this default behavior is generally what you'd
      expect; however, your input is most welcome.

      In any case, if you hit a situation where you must force Make to
      get the 8+3 DOS filenames in upper case, set FNCASE=y in the
      environment or in the Makefile.


   5. DOS-style pathnames.

      There are a lot of places throughout the program sources which
      make implicit assumptions about the pathname syntax.  In
      particular, the directories are assumed to be separated by `/',
      and any pathname which doesn't begin with a `/' is assumed to be
      relative to the current directory.  This port attempts to
      support DOS-style pathnames which might include the drive letter
      and use backslashes instead of forward slashes.  However, this
      support is not complete; I feel that pursuing this support too
      far might break some more important features, particularly if
      you use a Unix-style shell (where a backslash is a quote
      character).  I only consider support of backslashes desirable
      because some Makefiles invoke non-DJGPP programs which don't
      understand forward slashes.  A notable example of such programs
      is the standard programs which come with MSDOS.  Otherwise, you
      are advised to stay away from backslashes whenever possible.  In
      particular, filename globbing won't work on pathnames with
      backslashes, because the GNU `glob' library doesn't support them
      (backslash is special in filename wildcards, and I didn't want
      to break that).

      One feature which *does* work with backslashes is the filename-
      related built-in functions such as $(dir), $(notdir), etc.
      Drive letters in pathnames are also fully supported.



Bug reports:
-----------

   Bugs that are clearly related to the MSDOS/DJGPP port should be
   reported first on the comp.os.msdos.djgpp news group (if you cannot
   post to Usenet groups, write to the DJGPP mailing list,
   <djgpp@delorie.com>, which is an email gateway into the above news
   group).  For other bugs, please follow the procedure explained in
   the "Bugs" chapter of the Info docs.  If you don't have an Info
   reader, look up that chapter in the `make.i1' file with any text
   browser/editor.


   Enjoy,
                        Eli Zaretskii <eliz@is.elta.co.il>

\f
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