base url and SEF

Hi all, I'm currently parsing the variable $_SERVER['PHP_SELF'] to get the base url of a site. Example: http://www.example.com/~eric/program/index.php?option=abc What I'm interested in getting is "http://www.example.com/~eric/program/", which I am able to get currently. Questions" 1) Are there security implications in using $_SERVER['PHP_SELF'], and if so, how do I mitigate it? 2) Is using this method safe for all sorts of browsers/servers that run php? 3) If I install an SEF software so that my url looks like http://www.example.com/~eric/program/a/b/c ,what will $_SERVER['PHP_SELF'] show? Thanks. Eric