Underscore strings

<?php
    function string_to_underscore_name($string)
    {
	    $string = preg_replace('/[\'"]/', '', $string);
	    $string = preg_replace('/[^a-zA-Z0-9]+/', '_', $string);
	    $string = strtolower(trim($string, '_'));
	    return $string;
    }
    echo string_to_underscore_name("13: inside movie films```''''---\//\Bye!?");
    // Output: 13_inside_movie_films_bye
?>