PHP obtains several global variables of the domain name

//Get the current domain name:
echo $_SERVER['SERVER_NAME'];//Get the source URL, that is, click to go to the previous page URL of this page
echo " ";
echo $_SERVER["HTTP_REFERER"]; //Get the suffix of the previous page domain name
echo "";
echo $_SERVER['REQUEST_URI'];//Get the suffix of the current domain name
echo " ";
echo $_SERVER['HTTP_HOST'];//Get the current domain name
echo ""; //bbs.it-home.org
dirname(__FILE__);//Get the current file The physical path
dirname(__FILE__)."/../";//Get the upper-level physical path of the current file
exit;
?>