#!/usr/bin/perl
use strict;
use warnings;

open my $fh, ">", "mylock.$$" or die "open mylock.$$: $!";
sleep 2 until get_lock();
print "locked> ";
<>;
unlink "mylock";    # releases the lock
unlink "mylock.$$"; # just cleaning up

sub get_lock {
	link "mylock.$$", "mylock" and return 1;
	return (stat "mylock.$$" )[3] == 2;
}