"As an aside, I must say it's not easy finding info on Perl-style regex/grep if you're not actually coding in Perl. For the life of me I haven't been able to find authoritative info on setting delimiters, and was thrown by Privoxy's liberal use of things other than "/". And so on. Will keep learning!"

A good place to start would be "perlretut - Perl regular expressions tutorial". This has links to further, relevant information (including more detailed descriptions of the topics covered in the tutorial).

Here's the documentation for grep.

If you have questions arising from any of that documentation, feel free to ask but it would probably be better to raise them in a new thread. Also, the guidelines in "How do I post a question effectively?" will help in getting the best answers.