#!/usr/bin/perl -w

use strict;
use Fcntl qw(F_WRLCK SEEK_SET F_SETLKW);

open(F,"+< $ARGV[0]")
  or die "Couldn't lock myself: $!\n";
my $args = pack("sslli",F_WRLCK,SEEK_SET,0,0,$$);
fcntl(F,F_SETLKW,$args)
  or die "Couldn't lock: $!\n";

print "File locked\n";
sleep(1000);