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document (( problem more accurately

From: Paul Eggert
Subject: document (( problem more accurately
Date: Thu, 08 Feb 2007 15:43:27 -0800
User-agent: Gnus/5.1008 (Gnus v5.10.8) Emacs/21.4 (gnu/linux)

I installed this:

2007-02-08  Paul Eggert  <address@hidden>

        * doc/autoconf.texi (Parentheses): Mention problem with (( in

Index: doc/autoconf.texi
RCS file: /cvsroot/autoconf/autoconf/doc/autoconf.texi,v
retrieving revision 1.1131
diff -u -p -r1.1131 autoconf.texi
--- doc/autoconf.texi   7 Feb 2007 17:45:37 -0000       1.1131
+++ doc/autoconf.texi   8 Feb 2007 23:42:28 -0000
@@ -11896,9 +11896,13 @@ for the rationale.
 @section Parentheses in Shell Scripts
 @cindex Shell parentheses

-Beware of two opening parentheses in a row, as some shell
-implementations mishandle them.  For example, @samp{pdksh} 5.2.14
-misparses the following code:
+Beware of two opening parentheses in a row, as many shell
+implementations treat them specially.  Posix requires that the command
address@hidden((cat))} must behave like @samp{(cat)}, but many shells, including
+Bash and the Korn shell, treat @samp{((cat))} as an arithmetic
+expression equivalent to @samp{let "cat"}, and may or may not report an
+error when they detect that @samp{cat} is not a number.  As another
+example, @samp{pdksh} 5.2.14 misparses the following code:

 if ((true) || false); then

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