Regular Expressions
 

I'm wondering if there's a complete and accurate reference for all the various regular expressions in programs like sed, perl, grep, emacs, etc. Currently I just use Google, which usually brings up something that is inaccurate or talks about very basic/general regex. For instance, I'm confused as to why \w matches underscores _ in sed. This is very frustrating, and I haven't found a single resource that describes this. Thanks in advance for any help.

'man 7 regex' is quite clear.

\w is nowhere in that man page. It only specifies that word boundaries (which aren't even given as \b but [[:<:]] and [[:>:]]) include :alnum and underscores.

Well, the corresponding info page has some more information ('info regex' or other mirror)

eg. \w is mentioned in info page