Creating a lock file in sh?

[Robert Hartman]

In article <PABLO.91Apr17110430 at tofu-hut.csd.sgi.com> pablo at 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