A Grep-like Utility That Works on More than Text?

Nutria writes "This article got me thinking: What's a poor Unix-using guy to do, when he needs to grep text, compressed tarballs, OO.o documents, Debian archives, mime-encoded files, Evil Microsoft documents, PDF files, compressed AbiWord files, etc." Is there an extensible searching program for Unix that can handle a variety of different file-types? Search engines like ht://Dig can accomplish part of this task, however currently it doesn't index the whole file (just portions of the metadata). If you had to perform a substring search on a set of documents of different types, what tools would you use to accomplish this task?

Comments

How, indeed!

[Otter]

The same way everything else works!

1) Be had a half-decent version years ago.

2) Apple will have a reasonably robust version out soon.

3) Microsoft will have a more frustrating knock-off of Apple's version a few years later.

4) Four competing, incompatible open-source projects will copy the Apple and Microsoft implementations. When one of those companies sends a cease and desist letter to an open-source project that has shamelessly ripped off its trademarked name, Linux zealots will complain about how "intellectual property laws stifle our innovation"!