#! /user/bin/perl -w

use strict;
use Fcntl qw/:DEFAULT :flock/;

my $filename = "/test.lock";

if (sysopen(FH, $filename, O_RDWR | O_CREAT | O_EXCL))    {
    print "Process locked.\n";
    sleep(10);
}
else    {
    print "Waiting for lock.\n";
    while (!sysopen(FH, $filename, O_RDWR | O_CREAT | O_EXCL))    {};
    print "Got the lock.\n";
}

unlink($filename);
close(FH);