sub Counter ($) {
    local $/ = "\n";
    my             $fh;
    open           $fh, '+<', $_[0] or
    open           $fh, '>',  $_[0] or return undef;
    flock          $fh, 2;
    seek           $fh, 0, 0;
    my $counter = <$fh>;
    seek           $fh, 0, 0;
    truncate       $fh, 0;
    print          $fh ++$counter   or return undef;
    close          $fh              or return undef;
    return $counter;
}