creates a slug of any given string

utility.slug.php

<?php
/** 
  * Return URL-Friendly string slug
  * @param string $string 
  * @return string 
  */

function slug($string) {
    //Unwanted:  {UPPERCASE} ; / ? : @ & = + $ , . ! ~ * ' ( )
    $string = strtolower($string);
    //Strip any unwanted characters
    $string = preg_replace("/[^a-z0-9_\s-]/", "", $string);
    //Clean multiple dashes or whitespaces
    $string = preg_replace("/[\s-]+/", " ", $string);
    //Convert whitespaces and underscore to dash
    $string = preg_replace("/[\s_]/", "-", $string);
    return $string;
}