From: Meino Christian Cramer <Meino.Cramer@gmx.de>
To: schaefer@brasslantern.com
Cc: zsh-users@sunsite.dk
Subject: Re: Airthmetic confusion...
Date: Tue, 17 May 2005 16:57:49 +0200 (CEST) [thread overview]
Message-ID: <20050517.165749.74751175.Meino.Cramer@gmx.de> (raw)
In-Reply-To: <1050517034852.ZM26898@candle.brasslantern.com>
From: Bart Schaefer <schaefer@brasslantern.com>
Subject: Re: Airthmetic confusion...
Date: Tue, 17 May 2005 03:48:52 +0000
Thanks a lot for your explicit explanations.
Meino
> On May 17, 5:13am, Meino Christian Cramer wrote:
> }
> } I see that "0" is false and !0 is true...but...we
> } are doing arithmetic and not logical evaluation.
>
> No, that's not true.
>
> First of all, the closest thing to "logical" evaluation that the
> shell does is the &&, ||, etc., subexpressions WITHIN arithmetic
> expressions. The && and || constructs that test process success
> or failure are NOT "logical" operators -- for one thing, they do
> not obey the usual Boolean precedence rules. "set -e" is not a
> "logical" comparison by any stretch.
>
> Second, when you write (( expression )) then you are explicitly
> instructing the shell to do BOTH arithmetic evaluation AND shell
> expression success/failure. That's what the double parens MEAN,
> when not preceded by a dollar sign.
>
> If you want ONLY arithmetic evaluation, use $(( expression )),
> and apply the colon command if necessary, e.g.
>
> : $(( x = a - b ))
>
> or
>
> x=$(( a - b ))
>
> Those are both successful shell expressions that result in zero-
> value assignments to x.
>
> As with any other programming language, you have to write exactly
> what you mean, and you have to follow the language's semantic rules,
> not the rules as you think they should be.
>
> } As a sideffect a previously existant variable become inexistant by
> } assigning a "0"?
>
> What makes you believe that's happening? Assignments can only create
> variables, they can't unset them.
>
next prev parent reply other threads:[~2005-05-17 14:57 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-05-16 17:55 Meino Christian Cramer
2005-05-16 20:43 ` Matthias Berndt
2005-05-16 20:59 ` Mike Hernandez
2005-05-16 21:46 ` Dan Nelson
2005-05-17 1:19 ` Mike Hernandez
2005-05-16 23:39 ` Matthias Berndt
2005-05-17 3:13 ` Meino Christian Cramer
2005-05-17 3:48 ` Bart Schaefer
2005-05-17 11:26 ` Mike Hernandez
2005-05-17 14:57 ` Meino Christian Cramer [this message]
2005-05-17 3:14 ` Meino Christian Cramer
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20050517.165749.74751175.Meino.Cramer@gmx.de \
--to=meino.cramer@gmx.de \
--cc=schaefer@brasslantern.com \
--cc=zsh-users@sunsite.dk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/zsh/
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).