You might also take a look at Sed & Awk, co-authored by Daniel Robbin's father, Arnold Robbins.
The awk chapters in Bentley's _Programming Pearls_ and _More Programming Pearls_ and Peteris Krumins's Awk One-Liners series (http://www.catonmat.net/blog/awk-one-liners-explained-part-o...) are worth a read, as is the source for awk. (nawk, at least - haven't looked at gawk).