Get the directory of one php file

    $nowdir=$_SERVER["SCRIPT_FILENAME"];
        //echo $nowdir."<br>";
        /**
         * The below regulartion will only support windows system,
         * because in windows system if you use $_SERVER["SCRIPT_FILENAME"] to get
         * file's path,it will like "c:/xxx/xxx",but in linux the path will be
         * "/root/xxx/xxx"
         */
        preg_match('/(.*///)/si', $nowdir, $match );
        //echo $match[1] ;
        $rootdir=$match[1];