Regex Problem PHP Apache

[linchat]

I am trying to use AliasMatch to match a specific request

http://www.test.com/bob

Where bob is the directory. I only need AliasMatch to match that, bob can be any directory name though.

http://www.test.com/index.php (no alias match)
http://www.test.com/bob/index.php (no alias match)
http://www.test.com/bob (MATCH)

The below is one of many statements I have tried. Just need match on directories, not on files. Otherwise jpg's, gifs, will all be thrown into the mix and cause all kinds of problems.

AliasMatch ^/(.*[?/])$ /root/runme.php

Thanks in Advance