Needed some quick code to remove some characters from a URL field and replace them with underscores.
Found a short discussion on WebMasterWord that contained this code:
$old_pattern = array("/[^a-zA-Z0-9]/", "/_+/", "/_$/");
$new_pattern = array("_", "_", "");
$file_name = strtolower(preg_replace($old_pattern, $new_pattern , $text_title));