while (1)
{
    $new_size = -s $file;
    if ($new_size > $old_size) { # $old_size is defined before this loop
       if ( event_occured() ) {
           sleep($map_vTime);
           do_your_thing();
           $old_size = $new_size;
           }
       $old_size = $new_size;
       }
     sleep($normal_sleep_interval);
}