Setting up Route for Category-based RSS Feeds
Okay, I think that I have figured it out. Posting here for posterity. Based on the requirement above, I put these in my routes.php file.

'shows\/(?P&lt;parentSlug&gt;[a-zA-Z0-9\-\.]+)\/(?P&lt;childSlug&gt;[a-zA-Z0-9\-\.]+)\/feed' =&gt; 'categories/_shows.rss',


and

'shows\/(?P&lt;parentSlug&gt;[a-zA-Z0-9\-\.]+)\/feed' =&gt; 'categories/_shows.rss',


This gives me two variables. parentSlug and childSlug