经常在开发中会用到这些，在这里备份一下

// 获取域名或主机地址
echo $_SERVER['HTTP_HOST'] . "<br />";
// 获取网页地址
echo $_SERVER['PHP_SELF'] . "<br />";
// 获取网址参数
echo $_SERVER["QUERY_STRING"] . "<br />";
// 获取用户代理
echo $_SERVER['HTTP_REFERER'] . "<br />";
// 获取完整的url
echo 'http://' . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'] . "<br />";
echo 'http://' . $_SERVER['HTTP_HOST'] . $_SERVER['PHP_SELF'] . '?' . $_SERVER['QUERY_STRING'] . "<br />";
// 包含端口号的完整url
echo 'http://' . $_SERVER['SERVER_NAME'] . ':' .$_SERVER["SERVER_PORT"] . $_SERVER["REQUEST_URI"] . "<br />";
// 只取路径
$url='http://' . $_SERVER['SERVER_NAME'] . $_SERVER["REQUEST_URI"] . "<br />";
echo dirname($url);