Quick-and-dirty way to ensure only one instance of a shell script is running at a time

Question

What\'s a quick-and-dirty way to make sure that only one instance of a shell script is running at a given time?

Answer 1

You can use GNU Parallel for this as it works as a mutex when called as sem. So, in concrete terms, you can use:

sem --id SCRIPTSINGLETON yourScript

If you want a timeout too, use:

sem --id SCRIPTSINGLETON --semaphoretimeout -10 yourScript

Timeout of <0 means exit without running script if semaphore is not released within the timeout, timeout of >0 mean run the script anyway.

Note that you should give it a name (with --id) else it defaults to the controlling terminal.

GNU Parallel is a very simple install on most Linux/OSX/Unix platforms - it is just a Perl script.