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Re: no_clobber and error conditions
- X-seq: zsh-workers 22439
- From: Peter Stephenson <p.w.stephenson@xxxxxxxxxxxx>
- To: zsh-workers@xxxxxxxxxx (Zsh hackers list)
- Subject: Re: no_clobber and error conditions
- Date: Wed, 10 May 2006 20:12:32 +0100
- In-reply-to: Your message of "Wed, 10 May 2006 08:59:02 PDT." <060510085902.ZM11172@xxxxxxxxxxxxxxxxxxxxxx>
- Mailing-list: contact zsh-workers-help@xxxxxxxxxx; run by ezmlm
Bart Schaefer wrote:
> However, it appears that the error from noclobber does not "throw an
> exception," it merely causes the command to have exit status 1.
>
> That's not consistent with csh behavior (tcsh in this sample):
>
> [schaefer@toltec /tmp]$ ( set noclobber; echo > lockfile; echo oops )
> lockfile: File exists.
> [schaefer@toltec /tmp]$
> schaefer[537] ( setopt noclobber; echo > lockfile; echo oops )
> zsh: file exists: lockfile
> oops
> schaefer[538]
It is consistent with bash. The standard just says it "shall fail". I
couldn't see a formal definition of "fail", but it seems just to
indicate returning a non-zero status, as in
If a command fails during word expansion or redirection, its exit status
shall be greater than zero.
But a failure doesn't need to be atomically handled, does it? How about
revisiting:
echo >foo || { readonly THROW; THROW= 2>/dev/null; };
(where "readonly THROW" should be at the top of the function). Or, of
course, use throw and catch functions:
function lock() {
emulate -L zsh
setopt noclobber xtrace
integer ret=-1
autoload -U throw catch
while true; do
{
: >$1 || throw Exists
} always {
if ! catch Exists; then
if catch ''; then
ret=1
else
ret=0
fi
fi
}
(( ret >= 0 )) && return $ret
sleep 1
done
}
("return" in the middle of the always block doesn't work. I can't quite
make up my mind whether to be embarrassed or not. It depends how
seriously you take "Execution [after the always block] continues from
the result of the execution of try-list".)
--
Peter Stephenson <p.w.stephenson@xxxxxxxxxxxx>
Web page now at http://homepage.ntlworld.com/p.w.stephenson/
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