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

use Fcntl qw ( :flock ); 

open ( my $lock_this, '>', 'lockfile_flock' ) or die $!;

print "Enter to lock\n"; <>; 
print "Requesting EX lock\n"; 
flock ( $lock_this, LOCK_EX ); 
print "Lock acquired\n"; 
print "Enter to release\n"; <>; 
flock ( $lock_this, LOCK_UN ); 
print "Lock released\n";