I am an IT contractor with 14 years of experience. A few years ago I had an interview for a contract on the strength of the small exposure I had to UNIX Shell. I knew that to carry on paying the mortgage I was going to have to be pretty impressive in this area.
I already had the "Unix in a Nutshell" which is excellent, especially for understanding shells written by other people. However, I knew that I was going to need a framework of understanding if I was going to be able to knock a script together from scratch. I was also going to have to be able to read something that was presented in a very readable "start to finish" manner.
This book provided me with this basic understanding. Taking me from the description of the various flavours of Unix shell, through to the login process, regular expressions, pipes, redirection and then on to how the commands "work".
I will concede that there are some typos, and various features described that I have never found in any of the sites at which I've worked. But after a weekend of unremitting reading and taking notes, and rereading, this book got me a job and earned me money. That's the bottom line.
It is for experienced and capable IT professionals who have no broad understanding of the UNIX world. It will take you from a person with no UNIX credibility to someone who sounds like they've been doing it for a year or so. The commands and their options should be tackled with "UNIX in a Nutshell". With a book you can quickly flick from one page to another, cross referencing and sticking postits around the place - you can't do that with the man command.