From: Stephane Chazelas <Stephane_Chazelas@yahoo.fr>
To: Zsh hackers list <zsh-workers@sunsite.dk>,
Richard Hartmann <richih.mailinglist@gmail.com>,
Peter Stephenson <p.w.stephenson@ntlworld.com>
Subject: Re: arithmetic operator precedence
Date: Tue, 17 Jun 2008 15:35:59 +0100 [thread overview]
Message-ID: <20080617143559.GP5016@sc.homeunix.net> (raw)
In-Reply-To: <20080617132039.GK5016@sc.homeunix.net>
On Tue, Jun 17, 2008 at 02:20:39PM +0100, Stephane Chazelas wrote:
> On Tue, Jun 17, 2008 at 03:02:46PM +0200, Vincent Lefevre wrote:
> [...]
> > It is unspecified. So, the shell is right to choose how it sees it.
> >
> > > If $a contains an integer constant such as -3, then as per
> > > POSIX, $((a * 3)) should be the same as $(($a * 3)), that is
> > > $((-3 * 3)).
> >
> > No, POSIX does not say that. It happens to be the same thing here
> > just because of the properties of *, but you can't deduce anything
> > for extensions.
>
> It says $((x)) is meant to be the same as $(($x)) which I
> understand as any occurrance of a variable name (other than $-,
> $?, $0... obviously) in $((...)) should be the same as if the $
> was not ommited (when $x contains an integer constant).
[...]
It can't be that simple though, as in
x=-1; $((1 x))
which would be POSIX but fails in all shells.
Or
x=1; $((x = 1 + x))
which obviously is not meant to be the same as $(($x = 1 + $x))
So that
If the shell variable x contains a value that forms a valid
integer constant, then the arithmetic expansions "$((x))" and
"$(($x))" shall return the same value.
says either too little or too much to be useful.
--
Stéphane
next prev parent reply other threads:[~2008-06-17 14:36 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 [this message]
2008-06-17 15:05 ` Vincent Lefevre
2008-06-17 10:54 ` Vincent Lefevre
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