check_gnu_make

This macro searches for a GNU version of make. If a match is found, 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 variable _cv_gnu_make_command is set to the command to invoke GNU make if it exists, the empty string otherwise.

Here is an example of its use:

Makefile.in might contain:

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

    @ifGNUmake@ ifeq ($(DEPEND),$(wildcard $(DEPEND)))
    @ifGNUmake@ include $(DEPEND)
    @ifGNUmake@ endif

Then configure.in would normally contain:

    CHECK_GNU_MAKE()
    AC_OUTPUT(Makefile)

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):

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

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

AC_DEFUN(
        [CHECK_GNU_MAKE], [ AC_CACHE_CHECK( for GNU make,_cv_gnu_make_command,
                _cv_gnu_make_command='' ;
dnl Search all the common names for GNU make
                for a in "$MAKE" make gmake gnumake ; do
                        if test -z "$a" ; then continue ; fi ;
                        if  ( sh -c "$a --version" 2> /dev/null | grep GNU  2>&1 > /dev/null ) ;  then
                                _cv_gnu_make_command=$a ;
                                break;
                        fi
                done ;
        ) ;
dnl If there was a GNU version, then set @ifGNUmake@ to the empty string, '#' otherwise
        if test  "x$_cv_gnu_make_command" != "x"  ; then
                ifGNUmake='' ;
        else
                ifGNUmake='#' ;
                AC_MSG_RESULT("Not found");
        fi
        AC_SUBST(ifGNUmake)
] )

Copyright © 2002 John Darrington <j.darrington@elvis.murdoch.edu.au>

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.