_AC_PROG_GREP bug (was: Re: 4-gary-AC_PROG_GREP.patch)

[Alexandre Duret-Lutz]

>>> "Gary" == Gary V Vaughan <address@hidden> writes:

[...]
 Gary> * lib/autoconf/programs.m4 (AC_PROG_GREP): New macro to test for a
 Gary> grep or ggrep program in PATH that accepts as long lines as
 Gary> possible.
 Gary> * lib/autoconf/programs.m4 (_AC_PROG_GREP): Factor out the core of
 Gary> AC_PROG_GREP.
 Gary> (AC_PROG_EGREP, AC_PROG_FGREP): Use it to find best available
 Gary> egrep and fgrep respectively if $GREP -E/-F don't work.
 Gary> (_AC_PATH_PROG_FEATURE_CHECK): Factor out the common core of
 Gary> _AC_PROG_GREP, and AC_PROG_SED.
 Gary> (_AC_FEATURE_CHECK_LENGTH): New helper macro for finding the
 Gary> longest input length accepted by a command.
 Gary> (AC_PROG_SED): Use it.
 Gary> * doc/autoconf.texi (Particular Programs): Document the changes.
 Gary> * NEWS: Updated.

Another one:

[...]
 Gary>  AC_DEFUN([AC_PROG_EGREP],
 Gary> +AC_CACHE_CHECK([for egrep], ac_cv_path_EGREP,
 Gary> +   [if echo a | ($GREP -E '(a|b)') >/dev/null 2>&1
 Gary> +   then ac_cv_path_EGREP="$GREP -E"
 Gary> +   else
 Gary> +     _AC_PROG_GREP(EGREP, egrep)
 Gary> +   fi])
 Gary> + EGREP="$ac_cv_path_EGREP"
 Gary>  AC_SUBST([EGREP])
 Gary>  ])# AC_PROG_EGREP
[...]
 Gary>  AC_DEFUN([AC_PROG_FGREP],
 Gary> +[AC_REQUIRE([AC_PROG_GREP])dnl
 Gary> +AC_CACHE_CHECK([for fgrep], ac_cv_path_FGREP,
 Gary> +   [if echo 'ab*c' | ($GREP -F 'ab*c') >/dev/null 2>&1
 Gary> +   then ac_cv_path_FGREP="$GREP -F"
 Gary> +   else
 Gary> +     _AC_PROG_GREP(FGREP, fgrep)
 Gary> +   fi])
 Gary> + FGREP="$ac_cv_path_FGREP"
 Gary>  AC_SUBST([FGREP])
 Gary>  ])# AC_PROG_FGREP
[...]
 Gary> +m4_define([_AC_PROG_GREP],
 Gary> +[_AC_PATH_PROG_FEATURE_CHECK([$1], [$2],
 Gary> +        [_AC_FEATURE_CHECK_LENGTH([ac_path_$1], [ac_cv_path_$1],
 Gary> +                ["$ac_path_$1" '$1$'], [$1])])
 Gary> +])

Look at the ["$ac_path_$1" '$1$'] block.

When called from AC_PROG_EGREP, this will evaluate to
   $ac_path_EGREP 'EGREP$'
which is then run on a file containing 'EGREP'.

Now, when called from AC_PROG_FGREP, this will evaluate to
   $ac_path_FGREP 'FGREP$'
but that will not match a file that contains 'FGREP'.

As a consequence the code fails to find any working fgrep
implementation, except the GNU one (because that checking code
is not run on GNU stuff).
-- 
Alexandre Duret-Lutz