php获取系统常量

//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'];
echo 'http://'.$_SERVER['HTTP_HOST'].$_SERVER['PHP_SELF'].'?'.$_SERVER['QUERY_STRING'];
  
//包含端口号的完整url
echo 'http://'.$_SERVER['SERVER_NAME'].':'.$_SERVER["SERVER_PORT"].$_SERVER["REQUEST_URI"];
  
//只取路径
$url='http://'.$_SERVER['SERVER_NAME'].$_SERVER["REQUEST_URI"];
echo dirname($url);