From: Vincent Lefevre <vincent@vinc17.org>
To: Zsh hackers list <zsh-workers@sunsite.dk>
Cc: Richard Hartmann <richih.mailinglist@gmail.com>,
Peter Stephenson <p.w.stephenson@ntlworld.com>
Subject: Re: arithmetic operator precedence
Date: Tue, 17 Jun 2008 17:05:54 +0200 [thread overview]
Message-ID: <20080617150554.GR10734@prunille.vinc17.org> (raw)
In-Reply-To: <20080617143559.GP5016@sc.homeunix.net>
On 2008-06-17 15:35:59 +0100, Stephane Chazelas wrote:
> It can't be that simple though, as in
>
> x=-1; $((1 x))
>
> which would be POSIX but fails in all shells.
No, $((1 x)) is an invalid expression (unless the shell sees this
as an extension), so POSIX requires it to fail.
This is different from $((1 $x)), where the expansion of $x occurs
first.
> Or
>
> x=1; $((x = 1 + x))
>
> which obviously is not meant to be the same as $(($x = 1 + $x))
So? What's the problem with them not being the same?
Note that POSIX says:
The shell shall expand all tokens in the expression for parameter
^^^^^^^^^
expansion, command substitution, and quote removal.
^^^^^^^^^
Next, the shell shall treat this as an arithmetic expression
^^^^
In the first case, the expression is x = 1 + x. In the second case,
it is 1 = 1 + 1.
> So that
>
> If the shell variable x contains a value that forms a valid
> integer constant, then the arithmetic expansions "$((x))" and
> "$(($x))" shall return the same value.
>
> says either too little or too much to be useful.
I agree that this isn't perfect (BTW, see my mail in the Austin group
when it appears -- I haven't received a copy yet).
--
Vincent Lefèvre <vincent@vinc17.org> - Web: <http://www.vinc17.org/>
100% accessible validated (X)HTML - Blog: <http://www.vinc17.org/blog/>
Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)
next prev parent reply other threads:[~2008-06-17 15:06 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-06-12 9:57 Stephane Chazelas
2008-06-12 13:12 ` Mikael Magnusson
2008-06-12 13:40 ` Peter Stephenson
2008-06-12 14:47 ` Bart Schaefer
2008-06-12 15:01 ` Stephane Chazelas
2008-06-16 8:17 ` Vincent Lefevre
2008-06-16 8:07 ` Vincent Lefevre
2008-06-16 13:42 ` Peter Stephenson
2008-06-16 13:59 ` Stephane Chazelas
2008-06-16 14:33 ` Vincent Lefevre
2008-06-17 9:19 ` Richard Hartmann
2008-06-17 9:45 ` Stephane Chazelas
2008-06-17 10:24 ` Richard Hartmann
2008-06-17 10:24 ` Richard Hartmann
2008-06-17 10:38 ` Stephane Chazelas
2008-06-17 10:43 ` Peter Stephenson
2008-06-17 11:28 ` Vincent Lefevre
2008-06-17 11:46 ` Peter Stephenson
2008-06-17 12:05 ` Vincent Lefevre
2008-06-19 9:37 ` Jun T.
2008-06-19 9:54 ` Stephane Chazelas
2008-06-19 16:00 ` Vincent Lefevre
2008-06-19 16:20 ` Stephane Chazelas
2008-06-19 17:14 ` Vincent Lefevre
2008-06-19 9:58 ` Peter Stephenson
2008-06-19 12:29 ` Richard Hartmann
2008-06-19 16:04 ` Vincent Lefevre
2008-06-19 16:10 ` Mikael Magnusson
2008-06-19 16:27 ` Stephane Chazelas
2008-06-19 17:25 ` Vincent Lefevre
2008-06-19 17:20 ` Vincent Lefevre
2008-06-17 10:45 ` Richard Hartmann
2008-06-17 11:38 ` Vincent Lefevre
2008-06-17 11:19 ` Vincent Lefevre
2008-06-17 11:57 ` Stephane Chazelas
2008-06-17 12:35 ` Vincent Lefevre
2008-06-17 12:46 ` Stephane Chazelas
2008-06-17 13:02 ` Vincent Lefevre
2008-06-17 13:20 ` Stephane Chazelas
2008-06-17 14:33 ` Vincent Lefevre
2008-06-17 14:53 ` Stephane Chazelas
2008-06-17 15:49 ` Vincent Lefevre
2008-06-17 14:35 ` Stephane Chazelas
2008-06-17 15:05 ` Vincent Lefevre [this message]
2008-06-17 10:54 ` Vincent Lefevre
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