#!/usr/bin/perl

use strict;
use warnings;

use Fcntl qw(:flock);

my $file = shift;

open (F, "> $file") or die "Unable to open $file: $!";

my $lock_p = flock(F, LOCK_SH | LOCK_NB);

if ($lock_p) {
    print "Got shared lock on semaphore file!";
    my $wait = <>; # For testing - hold lock.
    flock(F, LOCK_UN) or warn "Problems unlocking $file: $!";
    exit 0;
} else {
    die "Ack! Didn't get a shared lock on $file: $!";
}