variables in conditions?

I've been unable to determine the answer to my question through various
resources and my trial-and-error tests haven't been conclusive.  Pardon
if this is a FAQ (but please answer me anyway). :)

Can I use variables in the conditions of a procmail recipe?  If so, I must
not be escaping it right or am otherwise just messing it up.. can you send
me an example of some variable usage in a recipe?

thanks,
kevin
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