From: ZyX <zyx.vim@gmail.com>
To: zsh-workers@zsh.org
Subject: Re: Check existence of a program
Date: Tue, 1 Feb 2011 23:21:02 +0300 [thread overview]
Message-ID: <201102012321.03053@-zyx> (raw)
In-Reply-To: <201102012212.10494@-zyx>
[-- Attachment #1: Type: Text/Plain, Size: 2215 bytes --]
Reply to message «Re: Check existence of a program»,
sent 22:12:09 01 February 2011, Tuesday
by ZyX:
Sorry, I should have read your question more correctly (and test $(cmd) variant
better). $(cmd) actually propagates exit code, so the reason is overriding of
$path as others have mentioned.
Original message:
> Reply to message «Check existence of a program»,
> sent 21:29:11 01 February 2011, Tuesday
> by Anonymous bin Ich:
>
> prog=exiftime
> path==$prog
> if [[ $? -ne 0 ]] ; then
> prog=identify
> path==$prog
> endif
>
> It works because zsh takes first = as assignment operator and expands
> second `=$prog' construct into a full path. If `=$prog' expansion fails,
> it throws an exception, exception prevents variable from being set and
> thus last expression fails what is indicated in $?.
>
> If you use $(cmd) construct, then though `cmd' fails, $(cmd) that does not
> care about exit code just expands into output of `cmd', so last expression
> (which is variable assignment, NOT `cmd') does not fail. Also note that
> `=$prog' does not produce new fork.
>
> Original message:
> > Hello!
> >
> > I am having trouble checking for existence of a program.
> >
> > This works:
> >
> > % cat working.zsh
> > #!/bin/zsh
> > set -x
> > prog="identify"
> > path=$(which ${prog})
> > %
> > % ./working.zsh
> > +./working.zsh:3> prog=identify
> > +./working.zsh:4> path=+./working.zsh:4> which identify
> > +./working.zsh:4> path=/usr/bin/identify
> > %
> >
> > But this doesn't:
> >
> > % cat notworking.zsh
> > #!/bin/zsh
> > set -x
> > prog="exiftime"
> > path=$(which ${prog})
> > if [[ ${?} -ne 0 ]]; then
> >
> > prog="identify"
> > path=$(which ${prog})
> >
> > fi
> > %
> > % ./notworking.zsh
> > +./notworking.zsh:3> prog=exiftime
> > +./notworking.zsh:4> path=+./notworking.zsh:4> which exiftime
> > +./notworking.zsh:4> path='exiftime not found'
> > +./notworking.zsh:5> [[ 1 -ne 0 ]]
> > +./notworking.zsh:6> prog=identify
> > +./notworking.zsh:7> path=+./notworking.zsh:7> which identify
> > +./notworking.zsh:7> path='identify not found'
> > %
> >
> > Any idea?
[-- Attachment #2: This is a digitally signed message part. --]
[-- Type: application/pgp-signature, Size: 198 bytes --]
prev parent reply other threads:[~2011-02-01 20:21 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <4D4850F7.6060205@gmail.com>
2011-02-01 19:12 ` ZyX
2011-02-01 20:21 ` ZyX [this message]
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=201102012321.03053@-zyx \
--to=zyx.vim@gmail.com \
--cc=zsh-workers@zsh.org \
/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).