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Re: mention DUALCASE

From: Paul Eggert
Subject: Re: mention DUALCASE
Date: Wed, 02 Feb 2005 16:32:32 -0800
User-agent: Gnus/5.1006 (Gnus v5.10.6) Emacs/21.3 (gnu/linux)

Thanks for that suggestion.  I installed the following more-general patch.

2005-02-02  Paul Eggert  <address@hidden>

        * doc/autoconf.texi (Special Shell Variables): Mention _,
        BIN_SH, DUALCASE.  Say that variables other than "status" are safe
        if they contain a lower-case letter.  The DUALCASE problem was
        reported by Ralf Wildenhues.

Index: autoconf.texi
RCS file: /cvsroot/autoconf/autoconf/doc/autoconf.texi,v
retrieving revision 1.872
retrieving revision 1.873
diff -p -u -r1.872 -r1.873
--- autoconf.texi       2 Feb 2005 23:47:34 -0000       1.872
+++ autoconf.texi       3 Feb 2005 00:31:33 -0000       1.873
@@ -10405,10 +10405,31 @@ Some shell variables should not be used,
 influence on the behavior of the shell.  In order to recover a sane
 behavior from the shell, some variables should be unset, but
 @command{unset} is not portable (@pxref{Limitations of Builtins}) and a
-fallback value is needed.  We list these values below.
+fallback value is needed.
+As a general rule, shell variable names containing a lower-case letter
+are safe; you can define and use these variables without worrying about
+their effect on the underlying system, and without worrying about
+whether the shell will change them unexpectedly.  (The exception is the
+shell variable @code{status}, as described below.)
+Here is a list of names that are known to cause trouble.  This list is
+not exhaustive, but you should be safe if you avoid the name
address@hidden and names containing only upper-case letters and
 @c Alphabetical order, case insensitive, `A' before `a'.
 @table @code
address@hidden _
+Many shells reserve @samp{$_} for various purposes, e.g., the name of
+the last command executed.
address@hidden BIN_SH
address@hidden BIN_SH
+In Tru64, if @env{BIN_SH} is set to @code{xpg4}, subsidiary invocations of
+the standard shell conform to Posix.
+Autoconf-generated scripts export this variable when they start up.
 @item CDPATH
 @evindex CDPATH
 When this variable is set it specifies a list of directories to search
@@ -10431,6 +10452,12 @@ In practice the shells that have this pr
 Autoconf-generated scripts automatically unset @code{CDPATH} if
 possible, so you need not worry about this problem in those scripts.
address@hidden DUALCASE
address@hidden DUALCASE
+In the MKS shell, case statements and file name generation are
+case-insensitive unless @code{DUALCASE} is nonzero.
+Autoconf-generated scripts export this variable when they start up.
 @item IFS
 @evindex IFS
 Don't set the first character of @code{IFS} to backslash.  Indeed,

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