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From: rhartman@thestepchild.sgi.com (Robert Hartman)
Newsgroups: comp.unix.shell
Subject: Re: Creating a lock file in sh?
Message-ID: <1991Apr17.201931.14536@odin.corp.sgi.com>
Date: 17 Apr 91 20:19:31 GMT
References: <PABLO.91Apr17110430@tofu-hut.csd.sgi.com>
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Organization: Silicon Graphics, Inc., Mountain View, CA
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In article <PABLO.91Apr17110430@tofu-hut.csd.sgi.com> pablo@sgi.com (Pablo Sanchez) writes:
>Hey there,
>
>    I apologize if this has been hashed over a bizzillion times but can
>someone please send me their Bourne-shell lock-file implementation.
>Thanks.

Aside from the fact that it isn't guaranteed over NFS, you can get some
measure of protection this way:

	if [ ! -w $file.lock ] ; then
		echo $user: $$ `date` > $file.lock
		if [ $$ -eq `awk '{print $2}' $file.lock` ] ; then
			# enter protected section
			# ...
			# exit protected section
		else
			echo "$file in use" ; exit 1
		fi
	else
		echo "$file in use" ; exit 1
	fi

-r