sostituire parametro in query string

[Tonybho]

Ho trovato e riadattato al mio scopo queste funzioni:

    function add_querystring_var($url, $key, $value) {
        $url = preg_replace('/(.*)(?|&)' . $key . '=[^&]+?(&)(.*)/i', '$1$2$4', $url . '&');
        $url = substr($url, 0, -1);
        if (strpos($url, '?') === false) {
            return ($url . '?' . $key . '=' . $value);
        } else {
            return ($url . '&' . $key . '=' . $value);
        }
    }
    
    function remove_querystring_var($url, $key) {
        $url = preg_replace('/(.*)(?|&)' . $key . '=[^&]+?(&)(.*)/i', '$1$2$4', $url . '&');
        $url = substr($url, 0, -1);
        return ($url);
    } 

Spero possano semplificare la vita a qualcuno.