Try this:
function getLastPathSegment($url) {
    $path = parse_url($url, PHP_URL_PATH); // to get the path from a whole URL
    $pathTrimmed = trim($path, '/'); // normalise with no leading or trailing slash
    $pathTokens = explode('/', $pathTrimmed); // get segments delimited by a slash
    if (substr($path, -1) !== '/') {
        array_pop($pathTokens);
    }
    return end($pathTokens); // get the last segment
}
    echo getLastPathSegment($_SERVER['REQUEST_URI']);
I've also tested it with a few URLs from the comments. I'm going to have to assume that all paths end with a slash, because I can not identify if /bob is a directory or a file. This will assume it is a file unless it has a trailing slash too.
echo getLastPathSegment('http://server.com/bla/wce/news.php'); // wce
echo getLastPathSegment('http://server.com/bla/wce/'); // wce
echo getLastPathSegment('http://server.com/bla/wce'); // bla