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Zack Weinberg 3b411849a0
m4sh: Require shell to support $(...) command substitution.
As of the 2020-11-07 update, config.sub and config.guess
unconditionally use $(...) command substitution; see
<https://lists.gnu.org/archive/html/config-patches/2020-11/msg00011.html>.

Therefore, add this to the set of required shell features, searched
for by _AS_DETECT_BETTER_SHELL.  On a system where /bin/sh doesn’t
support $(...), $CONFIG_SHELL will be set to one that does (and the
primary configure script will be re-executed using that shell).
AC_CANONICAL_* use $CONFIG_SHELL to execute config.guess/sub, so they
will keep working.  This also means that configure scripts and
third-party macros that use $(...) will quietly start working
correctly on such ancient systems.

The test code is simple, but sufficient to weed out Solaris 10’s
/bin/sh, which doesn’t support $(...) but *does* support shell
functions.

I’m not going to touch any of the existing uses of `...` command
substitution in Autoconf proper for now, but it might make sense to
bulk upgrade them early in the 2.71 release cycle; if nothing else,
it would remove a major obstacle to running shellcheck over our
scripts.

* lib/m4sugar/m4sh.m4 (_AS_MODERN_CMDSUBST_WORKS): New macro.
  (AS_INIT, AS_SHELL_SANITIZE): Call _AS_DETECT_REQUIRED for
  _AS_MODERN_CMDSUBST_WORKS.
* NEWS: Mention the requirement for $(...).
2020-11-09 15:15:23 -05:00
bin autoreconf: Support AM_GNU_GETTEXT_REQUIRE_VERSION 2020-11-09 13:22:28 -05:00
build-aux Check in install-sh as synced from automake (#110368) 2020-11-09 13:51:20 -05:00
doc autoreconf: Support AM_GNU_GETTEXT_REQUIRE_VERSION 2020-11-09 13:22:28 -05:00
lib m4sh: Require shell to support $(...) command substitution. 2020-11-09 15:15:23 -05:00
m4 make fetch 2020-09-03 12:08:31 -04:00
man Generate manpages directly from source code. 2020-08-21 16:23:32 -04:00
tests Make ‘forbidden tokens, basic’ test more robust. 2020-11-05 10:24:08 -05:00
.gitattributes maint: don't sync elisp-comp or missing from gnulib 2012-06-27 16:59:21 -06:00
.gitignore Check in install-sh as synced from automake (#110368) 2020-11-09 13:51:20 -05:00
.prev-version maint: post-release administrivia 2012-04-24 21:06:32 -06:00
.x-update-copyright maint: document use of copyright ranges 2011-01-04 16:32:25 -07:00
AUTHORS maint: make update-copyright 2020-01-01 11:45:50 -08:00
BUGS BUGS: Remove mention of old shells lacking functions. 2020-08-28 16:44:59 -04:00
cfg.mk Rewrite fetch.sh in Perl. 2020-09-11 14:51:00 -04:00
ChangeLog.0 Prefer HTTPS to FTP and HTTP 2017-09-16 17:48:51 -07:00
ChangeLog.1 Prefer HTTPS to FTP and HTTP 2017-09-16 17:48:51 -07:00
ChangeLog.2 Prefer HTTPS to FTP and HTTP 2017-09-16 17:48:51 -07:00
ChangeLog.3 maint: update URLs 2017-09-23 12:49:23 -07:00
configure.ac Add NetBSD /bin/sh to the -n whitelist. 2020-08-26 15:08:26 -04:00
COPYING Update links in COPYING, COPYINGv3, and COPYING.EXCEPTION. 2020-07-10 16:43:22 -04:00
COPYING.EXCEPTION Update links in COPYING, COPYINGv3, and COPYING.EXCEPTION. 2020-07-10 16:43:22 -04:00
COPYINGv3 Update links in COPYING, COPYINGv3, and COPYING.EXCEPTION. 2020-07-10 16:43:22 -04:00
GNUmakefile Partially revert e54e3f90: restore use of $(MAKE) in error message. 2020-08-04 08:46:59 -04:00
HACKING Update release advice 2020-06-29 17:08:27 -07:00
maint.mk make fetch 2020-06-29 17:08:26 -07:00
Makefile.am Generate manpages directly from source code. 2020-08-21 16:23:32 -04:00
NEWS m4sh: Require shell to support $(...) command substitution. 2020-11-09 15:15:23 -05:00
README maint: make update-copyright 2020-01-01 11:45:50 -08:00
README-alpha maint: make update-copyright 2020-01-01 11:45:50 -08:00
README-hacking * doc/autoconf.texi: Fix mishandling of `. 2020-07-13 12:55:19 -07:00
THANKS maint: make update-copyright 2020-01-01 11:45:50 -08:00
TODO * TODO: Add -Werror support. 2020-08-06 12:28:40 -07:00

-*- text -*-

Autoconf

Autoconf is an extensible package of M4 macros that produce shell
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