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

use Fcntl qw/:flock/;
use File::HomeDir qw//;

BEGIN {
    my $lockfile_path = File::HomeDir->my_data . '/my_lockfile';
    open LOCKFILE, '>', $lockfile_path;
    flock LOCKFILE, LOCK_EX | LOCK_NB
        or die "cannot acquire exclusive lock: $!\n";
}

# do something sensible here
print "Here I am\n";
sleep 10;
print "And there I go\n";

END {
    flock LOCKFILE, LOCK_UN;
    close LOCKFILE;
}