# As before ..
# ...
sub main
{
    my $start_mess = "===== Starting $TASK";
    $start_mess   .= " (@_)" if @_;
    $start_mess   .= " =====";
    error( $start_mess );
    my $FH;

    open( HIGHLANDER, ">$PID_FILE") or die( "Cannot write to $PID_FILE: $!" );
    {
	my $count = 0;
	{
	    flock HIGHLANDER, LOCK_EX | LOCK_NB and last;
	    sleep 1;
	    redo if ++$count < 3;
	    error( "Script is already running." );
            die( "Startup failed, PID file locked." );
        }
     }
    $FH = select(HIGHLANDER);
    $| = 1;
    select($FH);
    print HIGHLANDER $$;

# ..
# ..as before..