I purchased this book over a year ago now when I was doing a shell scripting course at university and couldnt understand a thing the lecturer was saying! This book took me out of the hole I was in and passed me the course, no doubt about it. As if that werent enough, I have recently undertaken the LPIC1 certification and again this book was worth its weight in gold. I was studying basic use of sed in the certification guide and deicded to brush up on regular expressions and the use of sed and again, out came this book and again, within a few hours it was all made clear. There is a large chapter on regular expressions thrown in so there's no need to buy a separate book on those unless your going in heavy, the material taught in this book is advanced enough for all but the most masochistic of people! Thoroughly good read very impressive book. Well worth the money. Its one of the most satisfying feelings when you finally crack a regexp and get the sed script to spit out what you need!