Fix `set -o posix' again (was: 1.5.22 fails to configure on AIX 5.1)

[Ralf Wildenhues]

Sorry for the delay.  Eliding libtool list.

* Paul Eggert wrote on Sun, Jan 15, 2006 at 01:57:29PM CET:
> Ralf Wildenhues <address@hidden> writes:
> 
> > | elif (set -o posix) >/dev/null 2>&1; then
> > |   set -o posix
> > | fi
> 
> Why does this hang under AIX?  Can you truss it, or strace it, or whatever?

D'oh.  It waits for stdin and finishes when given an EOF.  I can't
believe this either, I could swear I tried this last time and it did not
work.  Sorry for that noise.  :-/

> Does it work if we use two parens, e.g.,
> 
> elif ((set -o posix)) >/dev/null 2>&1; then
>   set -o posix
> fi

FWIW, yes, that returns immediately.

* Bruce Korb wrote on Sat, Jan 14, 2006 at 05:30:03PM CET:
> Ralf Wildenhues wrote:
> 
> >because, for example, OpenBSD uses a modified pdksh as /bin/sh, and one
> >of the modifications consists of not setting KSH_VERSION any more.  :-/
> >I am at a loss as how to detect this cleanly, suggestions welcome.
> 
> if test "X${RANDOM}" != "X${RANDOM}" -a "X${BASH_VERSION+set}" = "Xset"
> then echo this is ksh
> fi

Thanks!  OK to apply this patch, to avoid the fork&exec on uninvolved
systems similar to the code before?

Cheers,
Ralf

        * lib/m4sugar/m4sh.m4 (_AS_BOURNE_COMPATIBLE): Allow either of
        `BASH_VERSION', `KSH_VERSION', or `RANDOM' as indication of ksh
        or bash, to set the `posix' option.

Index: lib/m4sugar/m4sh.m4
===================================================================
RCS file: /cvsroot/autoconf/autoconf/lib/m4sugar/m4sh.m4,v
retrieving revision 1.156
diff -u -r1.156 m4sh.m4
--- lib/m4sugar/m4sh.m4 21 Jan 2006 09:09:46 -0000      1.156
+++ lib/m4sugar/m4sh.m4 21 Jan 2006 17:19:39 -0000
@@ -169,7 +169,8 @@
   # is contrary to our usage.  Disable this feature.
   alias -g '${1+"address@hidden"}'='"address@hidden"'
   setopt NO_GLOB_SUBST
-elif (set -o posix) >/dev/null 2>&1; then
+elif test -n "${BASH_VERSION+set}${KSH_VERSION+set}${RANDOM+set}" &&
+     (set -o posix) >/dev/null 2>&1; then
   set -o posix
 fi
 BIN_SH=xpg4; export BIN_SH # for Tru64