About filtering messages

[reader]

I posted about this earlier and never saw a response, maybe it is so
painfully obvious I should know how... but I don't know or maybe have
forgotten how. 

I want to filter newsgroups for a specific author and take some action
on that authors posts automatically.  

I don't mean to kill or score or whatever, I want to grab the content
and keep it somewhere.  Not like keeping in the agent sense but
copying the content and a few headers to a file somewhere.