@node ax_check_gnu_make
@unnumberedsec ax_check_gnu_make

@majorheading Synopsis

@smallexample
AX_CHECK_GNU_MAKE([run-if-true],[run-if-false])
@end smallexample

@majorheading Description

This macro searches for a GNU version of make. If a match is found:

@smallexample
  * The makefile variable `ifGNUmake' is set to the empty string, otherwise
    it is set to "#". This is useful for including a special features in a
    Makefile, which cannot be handled by other versions of make.
  * The makefile variable `ifnGNUmake' is set to #, otherwise
    it is set to the empty string. This is useful for including a special
    features in a Makefile, which can be handled
    by other versions of make or to specify else like clause.
  * The variable `_cv_gnu_make_command` is set to the command to invoke
    GNU make if it exists, the empty string otherwise.
  * The variable `ax_cv_gnu_make_command` is set to the command to invoke
    GNU make by copying `_cv_gnu_make_command`, otherwise it is unset.
  * If GNU Make is found, its version is extracted from the output of
    `make --version` as the last field of a record of space-separated
    columns and saved into the variable `ax_check_gnu_make_version`.
  * Additionally if GNU Make is found, run shell code run-if-true
    else run shell code run-if-false.
@end smallexample

Here is an example of its use:

Makefile.in might contain:

@smallexample
  # A failsafe way of putting a dependency rule into a makefile
  $(DEPEND):
          $(CC) -MM $(srcdir)/*.c > $(DEPEND)
@end smallexample

@smallexample
  @@ifGNUmake@@ ifeq ($(DEPEND),$(wildcard $(DEPEND)))
  @@ifGNUmake@@ include $(DEPEND)
  @@ifGNUmake@@ else
  fallback code
  @@ifGNUmake@@ endif
@end smallexample

Then configure.in would normally contain:

@smallexample
  AX_CHECK_GNU_MAKE()
  AC_OUTPUT(Makefile)
@end smallexample

Then perhaps to cause gnu make to override any other make, we could do
something like this (note that GNU make always looks for GNUmakefile
first):

@smallexample
  if  ! test x$_cv_gnu_make_command = x ; then
          mv Makefile GNUmakefile
          echo .DEFAULT: > Makefile ;
          echo \  $_cv_gnu_make_command \$@@ >> Makefile;
  fi
@end smallexample

Then, if any (well almost any) other make is called, and GNU make also
exists, then the other make wraps the GNU make.

@majorheading Source Code

Download the
@uref{http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=blob_plain;f=m4/ax_check_gnu_make.m4,latest
version of @file{ax_check_gnu_make.m4}} or browse
@uref{http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=history;f=m4/ax_check_gnu_make.m4,the
macro's revision history}.

@majorheading License

@w{Copyright @copyright{} 2008 John Darrington @email{j.darrington@@elvis.murdoch.edu.au}} @* @w{Copyright @copyright{} 2015 Enrico M. Crisostomo @email{enrico.m.crisostomo@@gmail.com}}

Copying and distribution of this file, with or without modification, are
permitted in any medium without royalty provided the copyright notice
and this notice are preserved. This file is offered as-is, without any
warranty.