PHP利用REFERER根居访问来地址进行页面跳转

<?php
$referHost = parse_url($_SERVER['HTTP_REFERER'], PHP_URL_HOST);
$validDomain = 'img.jbzj.com';
$valid = strstr($referHost, $validDomain) == $validDomain;
if(!empty($valid)){
    echo '<script>location.href="http://s.jb51.net";</script>';
    exit;
}