The book best for people who use regular expressions in more than one language/application. When I was a Perl programmer, I rarely looked at the Perl section, but did look at the javascript, grep, and sed sections all the time. Having a consistent format for each section should theoretically make it easier for you to apply your regex knowledge in whatever tool you're using (it does for me at least). I wrote the second edition primarily to add Apache and Ruby sections for myself, but also updated everything else with feedback and changes since the first edition.
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I wrote the pocket reference and also this best practices article for writing regular expressions. It's the habits I developed to avoid poking my own eyes out: http://www.onlamp.com/pub/a/onlamp/2003/08/21/regexp.html
It does cover grep and sed (and awk) but not emacs. Sorry about not covering the emacs. I'll give that some consideration if we do a third edition.
The book best for people who use regular expressions in more than one language/application. When I was a Perl programmer, I rarely looked at the Perl section, but did look at the javascript, grep, and sed sections all the time. Having a consistent format for each section should theoretically make it easier for you to apply your regex knowledge in whatever tool you're using (it does for me at least). I wrote the second edition primarily to add Apache and Ruby sections for myself, but also updated everything else with feedback and changes since the first edition.