php 获取文件绝对路径

echo $_SERVER['PHP_SELF'];
echo "<br/>";
echo str_replace("/","\\",$_SERVER['PHP_SELF']);
echo "<br/>";
echo __FILE__;
echo "<br/>";
define("WWWROOT",str_ireplace(str_replace("/","\\",$_SERVER['PHP_SELF']),'',__FILE__)."\\");
echo WWWROOT ;
echo "<br/>";
echo str_replace("/","\\",$_SERVER['DOCUMENT_ROOT']."\\");