using procmail to filter content

Hi i would like to find out how can i write a procmail rule to filter based on the email content.i was unable to locate any similar threads that does filtering based on the content.would appreciate any pointers. thanks

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* ^From: Machine1 <machine1@aaa.com>
# i will have a string "machine1.log" in the content
Email_from_M1_log


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* ^From: Machine1 <machine1@aaa.com>
# i will have a string "machine1.result" in the content
Email_from_M1_result

An old but relevant tutorial:
http://www.stimpy.net/procmail/tutorial/

An excellent source of Procmail recipes:
http://lipas.uwasa.fi/~ts/info/proctips.html

As for content filtering take a look at:

In particular, the "Scope of matching" section.

HTH

Cheers,
ZB