Recipe to test from "From" and "To" being equal?

I'd like to be able to test for "From:|Reply-To:" and "^TO" being 
identical -- I've noticed that's the case with many spams, and 
almost never for anything else.  But I can't figure out how one 
would do that in procmail.  Is there a way to extract the contents
of a header and assign them to a variable without calling a perl
program?  Or is there another obvious way to do this which I'm
missing?

Thanks!

Catherine