From: Tim Writer <tim@starnix.com>
To: Lloyd Zusman <ljz@asfast.com>
Cc: zsh-users@sunsite.dk
Subject: Re: File locking within zsh?
Date: 09 May 2006 23:31:54 -0400 [thread overview]
Message-ID: <ltd5emv9lh.fsf@newsol.starnix.com> (raw)
In-Reply-To: <87r7324zyh.fsf@asfast.com>
Lloyd Zusman <ljz@asfast.com> writes:
> Do any of you know of any functions, primitives, tricks, hacks, or even
> outright abominations which will allow me to do cooperative file locking
> from within zsh?
>
> I know that I can do this with a number of compiled executables, but I'm
> looking for a zsh-only solution.
>
> Assuming some sort of zsh locking operator called "lock", consider
> this example (within a zsh script):
>
> lock -x -t 0 file # for this example of a hypothetical operator, '-x'
> # means to wait until I get an exclusive lock, and
> # '-t 0' means no time out
> print foo bar baz >>file
> # do a whole lot of other stuff to "file"
> unlock file # release the lock
>
> In this example, any other zsh script which asks for an exclusive lock
> on "file" using this hypothetical "lock" operator will block until the
> "unlock" operator has been invoked.
>
> Can this be done somehow in zsh, or do I have to rely on a compiled
> executable to accomplish this?
The usual way to lock within shell scripts is to use ln. This works on all
UNIX like systems because creating a hard link (with ln) is an atomic
operation which fails if the target already exists. Your example above can be
written like this:
while ! ln file file.lock 2>/dev/null
do
sleep 1
done
# Lock obtained
print foo bar baz >>file
# do a whole lot of other stuff to "file"
rm -f file.lock
# Lock released
Wrapping this idiom into lock/unlock functions is left as an exercise for the
reader. :-)
--
tim writer <tim@starnix.com> starnix inc.
647.722.5301 toronto, ontario, canada
http://www.starnix.com professional linux services & products
next prev parent reply other threads:[~2006-05-10 3:32 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-05-09 22:04 Lloyd Zusman
2006-05-10 3:31 ` Tim Writer [this message]
2006-05-10 5:59 ` Brian K. White
2006-05-10 10:02 ` Lloyd Zusman
2006-05-10 22:04 ` Tim Writer
2006-05-11 3:41 ` Bart Schaefer
2006-05-11 14:25 ` Tim Writer
2006-05-11 15:01 ` Peter Stephenson
2006-05-12 4:22 ` Tim Writer
2006-05-12 9:17 ` Subshells and parameters (was: File locking within zsh?) Vincent Lefevre
2006-05-12 12:09 ` Subshells and parameters Lloyd Zusman
2006-05-12 23:09 ` Vincent Lefevre
2006-05-13 2:05 ` Lloyd Zusman
2006-05-17 14:24 ` Vincent Lefevre
2006-05-17 15:42 ` Bart Schaefer
2006-05-17 16:07 ` Vincent Lefevre
2006-05-13 2:10 ` Dan Nelson
2006-05-11 16:13 ` File locking within zsh? Brian K. White
2006-05-10 17:13 ` Vincent Lefevre
2006-05-11 15:45 ` Brian K. White
2006-05-12 7:54 ` Vincent Lefevre
2006-05-12 19:40 ` Tim Writer
2006-05-12 23:24 ` Vincent Lefevre
2006-05-10 21:53 ` Tim Writer
2006-05-10 6:29 ` DervishD
2006-05-10 10:02 ` Lloyd Zusman
2006-05-10 21:21 ` DervishD
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