Allow configuration choice in syscmd shell.

* ltdl/m4/m4-syscmd.m4: New file.
* configure.ac (M4_SYSCMD): Use it to provide
--with-syscmd-shell.
(AC_CHECK_HEADERS_ONCE): No longer need to worry about
<sys/wait.h>.
* modules/m4.c (syscmd): Use it to avoid hard-coding the shell
location.
* modules/gnu.c (esyscmd): Likewise.
* doc/m4.texinfo (Syscmd, Esyscmd): Document this.
* README: Document new configure option.
* NEWS: Likewise.

Signed-off-by: Eric Blake <ebb9@byu.net>
(cherry picked from commit 060b5319b3452a2464eea1defc5fae608a12b574)

8 files changed, 122 insertions, 19 deletions

diff --git a/ChangeLog b/ChangeLog
index b5f6487a..30f1c16e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,18 @@
 2009-03-13  Eric Blake  <ebb9@byu.net>
 
+	Allow configuration choice in syscmd shell.
+	* ltdl/m4/m4-syscmd.m4: New file.
+	* configure.ac (M4_SYSCMD): Use it to provide
+	--with-syscmd-shell.
+	(AC_CHECK_HEADERS_ONCE): No longer need to worry about
+	<sys/wait.h>.
+	* modules/m4.c (syscmd): Use it to avoid hard-coding the shell
+	location.
+	* modules/gnu.c (esyscmd): Likewise.
+	* doc/m4.texinfo (Syscmd, Esyscmd): Document this.
+	* README: Document new configure option.
+	* NEWS: Likewise.
+
 	Use gnulib pipe module instead of popen(3).
 	* ltdl/m4/gnulib-cache.m4: Import pipe and wait-process modules.
 	* modules/gnu.c (M4_SYSVAL_EXITBITS, M4_SYSVAL_TERMSIGBITS):
diff --git a/NEWS b/NEWS
index d2d42b54..4c6a76a7 100644
--- a/NEWS
+++ b/NEWS
@@ -355,6 +355,9 @@ contains the following beta features that were deemed worth deferring until
    `m4 --debugfile=trace file', not `m4 file --debugfile trace'.  This
    change does not affect the deprecated `-o'/`--error-output' option.
 
+** The `syscmd' and `esyscmd' builtins can be configured to use an
+   alternate shell, via the new `configure' option `--with-syscmd-shell'.
+
 ** A number of portability improvements inherited from gnulib.
 
 * Noteworthy changes in Version 1.4.12 (2008-10-10) [stable]
diff --git a/README b/README
index 390de384..a128a02c 100644
--- a/README
+++ b/README
@@ -44,6 +44,12 @@ host architecture.  The implementation uses libltdl interface, details of
 which are in the libtool manual.  See file `modules/README' for a more
 detailed description.
 
+By default, the `syscmd' and `esyscmd' macros try to use the first
+instance of `sh' found by `command -p getconf PATH' at configure time,
+with a default of `/bin/sh'.  If that default is inappropriate, you
+can use `./configure --with-syscmd-shell=location' to specify the
+shell to use.
+
 By using `./configure --with-dmalloc', GNU m4 is linked with Gray
 Watson's dmalloc package.  It is a debugging option for finding memory
 management problems.  Gray Watson's dmalloc package is available at
@@ -79,7 +85,8 @@ set of tests.
 
 ========================================================================
 
-Copyright (C) 2000, 2005, 2006, 2007 Free Software Foundation, Inc.
+Copyright (C) 2000, 2005, 2006, 2007, 2009 Free Software Foundation,
+Inc.
 
 Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.2 or
diff --git a/configure.ac b/configure.ac
index d8962cc6..ba57e399 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,6 +1,6 @@
 # Configure template for GNU m4.			-*-Autoconf-*-
-# Copyright (C) 1991, 1992, 1993, 1994, 2000, 2001, 2002, 2004, 2005, 2006,
-# 2007, 2008 Free Software Foundation, Inc.
+# Copyright (C) 1991, 1992, 1993, 1994, 2000, 2001, 2002, 2004, 2005,
+# 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
 #
 # This file is part of GNU M4.
 #
@@ -183,7 +183,7 @@ AC_CHECK_SIZEOF([long long int])
 ## ------------------------- ##
 ## C headers required by M4. ##
 ## ------------------------- ##
-AC_CHECK_HEADERS_ONCE([limits.h sys/wait.h])
+AC_CHECK_HEADERS_ONCE([limits.h])
 
 if test $ac_cv_header_stdbool_h = yes; then
   INCLUDE_STDBOOL_H='#include <stdbool.h>'
@@ -209,9 +209,14 @@ AC_FUNC_STRFTIME
 AC_CHECK_FUNCS_ONCE([getcwd gethostname mktime uname])
 AC_CHECK_FUNCS_ONCE([setenv unsetenv putenv clearenv])
 
+
+## ------------------ ##
+## Configure options. ##
+## ------------------ ##
+
 M4_LIB_GMP
 AM_CONDITIONAL([USE_GMP], [test "x$USE_GMP" = xyes])
-
+M4_SYSCMD
 
 
 ## -------- ##
diff --git a/doc/m4.texinfo b/doc/m4.texinfo
index 7f7bb3f3..486186e9 100644
--- a/doc/m4.texinfo
+++ b/doc/m4.texinfo
@@ -8052,6 +8052,15 @@ Prior to executing the command, @code{m4} flushes its buffers.
 The default standard input, output and error of @var{shell-command} are
 the same as those of @code{m4}.
 
+By default, the @var{shell-command} will be used as the argument to the
+@option{-c} option of the @command{/bin/sh} shell (or the version of
+@command{sh} specified by @samp{command -p getconf PATH}, if your system
+supports that).  If you prefer a different shell, the
+@command{configure} script can be given the option
+@option{--with-syscmd-shell=@var{location}} to set the location of an
+alternative shell at @acronym{GNU} @code{m4} installation; the
+alternative shell must still support @option{-c}.
+
 When the @option{--safer} option (@pxref{Operation modes, , Invoking
 m4}) is in effect, @code{syscmd} results in an error, since otherwise an
 input file could execute arbitrary code.
@@ -8123,6 +8132,15 @@ the same as those of @code{m4}.  The error output of @var{shell-command}
 is not a part of the expansion: it will appear along with the error
 output of @code{m4}.
 
+By default, the @var{shell-command} will be used as the argument to the
+@option{-c} option of the @command{/bin/sh} shell (or the version of
+@command{sh} specified by @samp{command -p getconf PATH}, if your system
+supports that).  If you prefer a different shell, the
+@command{configure} script can be given the option
+@option{--with-syscmd-shell=@var{location}} to set the location of an
+alternative shell at @acronym{GNU} @code{m4} installation; the
+alternative shell must still support @option{-c}.
+
 When the @option{--safer} option (@pxref{Operation modes, , Invoking
 m4}) is in effect, @code{esyscmd} results in an error, since otherwise
 an input file could execute arbitrary code.
diff --git a/ltdl/m4/m4-syscmd.m4 b/ltdl/m4/m4-syscmd.m4
new file mode 100644
index 00000000..3feddb83
--- /dev/null
+++ b/ltdl/m4/m4-syscmd.m4
@@ -0,0 +1,59 @@
+#                                                            -*- Autoconf -*-
+# m4-syscmd.m4 -- Allow choice of syscmd shell.
+# Written by Eric Blake <ebb9@byu.net>
+#
+# Copyright (C) 2009 Free Software Foundation, Inc
+#
+# This file is part of GNU M4.
+#
+# GNU M4 is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# GNU M4 is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# serial 1
+
+# M4_SYSCMD
+# ---------
+# Allow user to choose different shell than /bin/sh for e?syscmd.
+AC_DEFUN([M4_SYSCMD],
+[AC_MSG_CHECKING([[which shell to use for syscmd]])
+AC_ARG_WITH([syscmd-shell],
+  [AS_HELP_STRING([--with-syscmd-shell], [shell used by syscmd [/bin/sh]])],
+  [case $withval in
+    yes[)] with_syscmd_shell=no;;
+   esac], [with_syscmd_shell=no])
+if test "$with_syscmd_shell" = no ; then
+  with_syscmd_shell=/bin/sh
+  if test "$cross_compiling" != yes ; then
+dnl Give mingw a default that is more likely to be available.
+    AS_IF([AS_EXECUTABLE_P([/bin/sh])], [],
+      [if (cmd /c) 2>/dev/null; then with_syscmd_shell=cmd; fi])
+dnl Too bad _AS_PATH_WALK is not public.
+    M4_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+    for M4_dir in `if (command -p getconf PATH) 2>/dev/null ; then
+ command -p getconf PATH
+      else
+ echo "/bin$PATH_SEPARATOR$PATH"
+      fi`
+    do
+      IFS=$M4_save_IFS
+      test -z "$M4_dir" && continue
+      AS_EXECUTABLE_P(["$M4_dir/sh"]) \
+ && { with_syscmd_shell=$M4_dir/sh; break; }
+    done
+    IFS=$M4_save_IFS
+  fi
+fi
+AC_MSG_RESULT([$with_syscmd_shell])
+AC_DEFINE_UNQUOTED([M4_SYSCMD_SHELL], ["$with_syscmd_shell"],
+  [Shell used by syscmd and esyscmd, must accept -c argument.])
+])
diff --git a/modules/gnu.c b/modules/gnu.c
index e833f552..5650c727 100644
--- a/modules/gnu.c
+++ b/modules/gnu.c
@@ -639,9 +639,6 @@ M4BUILTIN_HANDLER (debugmode)
 }
 
 
-/* FIXME */
-#define SYSCMD_SHELL "/bin/sh"
-
 /* Same as the sysymd builtin from m4.c module, but expand to the
    output of SHELL-COMMAND. */
 
@@ -666,7 +663,6 @@ M4BUILTIN_HANDLER (esyscmd)
       int sig_status;
       const char *prog_args[4] = { "sh", "-c" };
       const char *caller;
-      const char *shell = SYSCMD_SHELL;
 
       if (m4_get_safer_opt (context))
 	{
@@ -686,13 +682,16 @@ M4BUILTIN_HANDLER (esyscmd)
 
       m4_sysval_flush (context, false);
 #if W32_NATIVE
-      shell = prog_args[0] = "cmd";
-      prog_args[1] = "/c";
+      if (strstr (M4_SYSCMD_SHELL, "cmd"))
+	{
+	  prog_args[0] = "cmd";
+	  prog_args[1] = "/c";
+	}
 #endif
       prog_args[2] = cmd;
       caller = m4_info_name (me);
       errno = 0;
-      child = create_pipe_in (caller, shell/*FIXME*/, (char **) prog_args,
+      child = create_pipe_in (caller, M4_SYSCMD_SHELL, (char **) prog_args,
 			      NULL, false, true, false, &fd);
       if (child == -1)
 	{
diff --git a/modules/m4.c b/modules/m4.c
index d4a58702..394abf3d 100644
--- a/modules/m4.c
+++ b/modules/m4.c
@@ -409,9 +409,6 @@ M4BUILTIN_HANDLER (defn)
 /* This section contains macros to handle the builtins "syscmd"
    and "sysval".  */
 
-/* FIXME */
-#define SYSCMD_SHELL "/bin/sh"
-
 /* Exit code from last "syscmd" command.  */
 /* FIXME - we should preserve this value across freezing.  See
    http://lists.gnu.org/archive/html/bug-m4/2006-06/msg00059.html
@@ -483,7 +480,6 @@ M4BUILTIN_HANDLER (syscmd)
   int status;
   int sig_status;
   const char *prog_args[4] = { "sh", "-c" };
-  const char *shell = SYSCMD_SHELL;
 
   if (m4_get_safer_opt (context))
     {
@@ -502,12 +498,15 @@ M4BUILTIN_HANDLER (syscmd)
     }
   m4_sysval_flush (context, false);
 #if W32_NATIVE
-  shell = prog_args[0] = "cmd";
-  prog_args[1] = "/c";
+  if (strstr (M4_SYSCMD_SHELL, "cmd"))
+    {
+      prog_args[0] = "cmd";
+      prog_args[1] = "/c";
+    }
 #endif
   prog_args[2] = cmd;
   errno = 0;
-  status = execute (m4_info_name (me), shell/*FIXME*/, (char **) prog_args,
+  status = execute (m4_info_name (me), M4_SYSCMD_SHELL, (char **) prog_args,
 		    false, false, false, false, true, false, &sig_status);
   if (sig_status)
     {