Re: "The `-a', `-o', `(', and `)' operands are not portable": please clarify

[Eric Blake]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

According to Reuben Thomas on 8/4/2009 3:53 PM:

[revisiting an old thread]

> 2009/8/4 Eric Blake <address@hidden>:
>>> What I'd like therefore is a rationale: if -a, -o and parentheses are
>>> not in POSIX 1990, please say so
>> [beautiful rationale from Eric]
> 
> Thanks Eric. Could a brief summary of this go in the manual? Something like:
> 
> "widely unimplemented and deprecated in POSIX 2008"

Yes, I'm committing this:

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.9 (Cygwin)
Comment: Public key at home.comcast.net/~ericblake/eblake.gpg
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/

iEYEARECAAYFAkqpsbMACgkQ84KuGfSFAYAMTwCg0sfchovG8UauIeDsWR1GEtjp
slAAoJF+PmIfLFpj9cwUXf9vbmA9GOkY
=rn56
-----END PGP SIGNATURE-----

>From 841c01f9953cb97b0bfa9d7da042d43ede3b1099 Mon Sep 17 00:00:00 2001
From: Eric Blake <address@hidden>
Date: Thu, 10 Sep 2009 20:05:21 -0600
Subject: [PATCH] Clarify portability pitfall of test.

* doc/autoconf.texi (Limitations of Builtins) <test>: Give more
reasons why -a and -o are not portable.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog         |    6 ++++++
 doc/autoconf.texi |   18 ++++++++++++------
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index d074681..ff99666 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2009-09-10  Eric Blake  <address@hidden>
+
+       Clarify portability pitfall of test.
+       * doc/autoconf.texi (Limitations of Builtins) <test>: Give more
+       reasons why -a and -o are not portable.
+
 2009-09-04  Reuben Thomas <address@hidden>  (tiny change)

        Mention the Autoconf archive.
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 6f06577..36eba53 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -16380,12 +16380,18 @@ Limitations of Builtins
 character.

 The @option{-a}, @option{-o}, @samp{(}, and @samp{)} operands are not
-portable and should be avoided.  Thus, portable uses of @command{test}
-should never have more than four arguments, and scripts should use shell
-constructs like @samp{&&} and @samp{||} instead.  If you combine
address@hidden&&} and @samp{||} in the same statement, keep in mind that they
-have equal precedence, so it is often better to parenthesize even when
-this is redundant.  For example:
+present in all implementations, and have been marked obsolete by Posix
+2008.  This is because there are inherent ambiguities in using them.
+For example, @samp{test "$1" -a "$2"} looks like a binary operator to
+check whether two strings are both non-empty, but if @samp{$1} is the
+literal @samp{!}, then some implementations of @command{test} treat it
+as a negation of the unary operator @option{-a}.
+
+Thus, portable uses of @command{test} should never have more than four
+arguments, and scripts should use shell constructs like @samp{&&} and
address@hidden||} instead.  If you combine @samp{&&} and @samp{||} in the same
+statement, keep in mind that they have equal precedence, so it is often
+better to parenthesize even when this is redundant.  For example:

 @smallexample
 # Not portable:
-- 
1.6.3.3.334.g916e1