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

my $pidfile="testfile.pid";
my $scriptname = $0;
my $pid="$$";

if(-e $pidfile)
{
    open(PFH, '<', $pidfile) or die $!;
    $pid =<PFH>;
    close(PFH);
    print"$scriptname already running: pid is $pid";
    exit;
}

open(PFH, '>', $pidfile) or die $!;
print(PFH $$);
close(PFH);

# do the job                                                                                             
sleep 13;

unlink($pidfile);