1. copy the adjacent php code into a standalone php file anywhere in your webspace. Change the variables in class Vars.
2. right at the bottom you'll find some perl. Copy into gm.cgi near the top immediately after the line:
The RSS files will now be rebuilt every time you run gm.cgi, eg when you add an entry to your Blog or run Rebuild
Convert Greymatter to RSS 2.0 and Atom 1.0 feeds
Convert Greymatter to RSS 2.0 and Atom 1.0 feeds: code for gm.cgi