source: vendor/grep/2.5.1a/autogen.sh

#!/bin/sh
# We want to support both legacy and current autoconf - this is a bit ugly...
AC_VERSION=`autoconf --version 2>&1 |head -n1 |sed -e "s/.* //;s/\.//;s/[a-z]//"`
if test -z "$AC_VERSION"; then
        echo "Warning: Couldn't determine autoconf version. Assuming a current version."
        AC_VERSION=252
fi
if test "$AC_VERSION" -lt 250; then
        rm -f acinclude.m4
        echo "#undef ssize_t" >acconfig.h
        for i in m4/*.m4; do
                if cat $i |grep -q "jm_"; then
                        cat $i >>acinclude.m4
                elif test ! -e `aclocal --print-ac-dir`/`basename $i`; then
                        cat $i >>acinclude.m4
                fi
        done
        aclocal
else
        aclocal -I m4
fi
autoheader
automake -a
if test "$AC_VERSION" -lt 250; then
        # Workaround for a bug in ancient versions of autoheader
        sed -e 's,#undef $,/* your autoheader is buggy */,g' config.hin >config.hin.new
        rm config.hin
        mv config.hin.new config.hin
        # Make sure config.hin doesn't get rebuilt after the workaround
        sed -e 's,@AUTOHEADER@,true,' Makefile.in >Makefile.in.new
        rm Makefile.in
        mv Makefile.in.new Makefile.in
fi
autoconf