2005-11-01  Stepan Kasal  <address@hidden>

	* doc/autoconf.texi (Limitations of Builtins): Document that
	"trap - SIG" is not yet portable.

Index: doc/autoconf.texi
===================================================================
RCS file: /cvsroot/autoconf/autoconf/doc/autoconf.texi,v
retrieving revision 1.932
diff -u -r1.932 autoconf.texi
--- doc/autoconf.texi	21 Oct 2005 05:46:50 -0000	1.932
+++ doc/autoconf.texi	1 Nov 2005 08:46:24 -0000
@@ -11365,7 +11365,7 @@
 RISC/OS} 4.52 refuses to do it.
 
 Don't use @samp{shift 2} etc.; it was not in the 7th Edition Bourne shell,
-and it is also absent in many pre-POSIX shells.
+and it is also absent in many pre-Posix shells.
 
 
 @item @command{source}
@@ -11488,6 +11488,27 @@
 It is safe to trap at least the signals 1, 2, 13, and 15.  You can also
 trap 0, i.e., have the @command{trap} run when the script ends (either via an
 explicit @command{exit}, or the end of the script).
+
+But even though Posix defines that the trap can be unset by
address@hidden - SIG}, the feature is not widely supported yet.
+But it si safe to use @samp{trap '' SIG} to ignore the signal; in particular,
address@hidden '' 0} is a portable way to clear the trap 0.
+
address@hidden
+The above is based on report:
+
+From: Kean Johnston <address@hidden>
+Date: Mon, 31 Oct 2005 23:53:23 -0800
+Cc: address@hidden, address@hidden, address@hidden
+Message-ID: <address@hidden>
+
+[trap - 0 doesn't work on] SCO OpenServer 5, SCO OpenServer 6, SCO UnixWare 2,
+SCO UnixWare 7. But I took a look around ...
+http://docs.sun.com/app/docs/doc/816-5165/6mbb0m9sa?a=view#indexterm-694
+(Solaris 10 man page for sh) doesn't support trap - either, but
+it does support the null string as an argument. Same with HPUX 11
+(http://docs.hp.com/en/B2355-90680/sh-bourne.1.html).
address@hidden ignore
 
 Although Posix is not absolutely clear on this point, it is widely
 admitted that when entering the trap @samp{$?} should be set to the exit