But wait, it gets better again!

You know how you can have that nifty __DATA__ block at the end of your script? It turns out you can lock that too :)

I've used this a number of times and it works just great.

#!/usr/bin/perl

use strict;
use Fcntl 'LOCK_EX', 'LOCK_NB';

unless ( flock DATA, LOCK_EX | LOCK_NB ) {
    print STDERR "Found duplicate script run. Stopping\n";
    exit(0);
}

...

1;





### DO NOT REMOVE THE FOLLOWING LINES ###

__DATA__
This exists to allow the locking code at the beginning of the file to work.
DO NOT REMOVE THESE LINES!

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