<p>Is there a good tutorial on using regular expressions, especially with <a href="http://en.wikipedia.org/wiki/Grep" rel="nofollow noreferrer">grep</a>? I tried googling for some, but most tutorials are too basic and cover things I already know.</p>

Here
is an introductory article.
Here
are some other tutorials.
The definitive book is
Mastering Regular Expressions
by J. Friedl:
alt text http://ecx.images-amazon.com/images/I/51fSgodb1uL._BO2,204,203,200_PIsitb-sticker-arrow-click,TopRight,35,-76_AA240_SH20_OU01_.jpg