<?php
/* Get URL */
$url = isset($_GET['url']) ? $_GET['url'] : 'unknown_url_can_put_alternative_url_here';

/* Decode URL */
$url = urldecode($url);

/* Check that our url is an correct url */
if (filter_var($url, FILTER_VALIDATE_URL)) {
    /* Do redirect */
    Header("Location: $url");
}