.htaccess regular expressions

Apparently, this doesn't work the way I thought it would.

RewriteRule ^([a-z]+)[\Z/] pre-$1.ext?

I want both examples to work like this:

1. /prog  -> pre-prog.ext?
2. /prog/ -> pre-prog.ext?

Am I going to have to bite the bullet and write two separate lines?


<?php
RewriteRule ^([a-z]+)/?$ pre-$1.ext?
?>