How deep down the rabbit hole do you really NEED to go? I had a serious need to get on top of regular expressions to solve one particular problem. I looked at several online tutorials which didn't take me where I needed to go, so I ordered Mastering Regular Expressions after reading the Amazon reviews. I always look at the negative reviews first. In spite of the negative reviews I ordered the book with an open mind.
When the book arrived I began reading it with enthusiasm. In the preface there is a small section on "How to Read This Book". I bought into the author's suggestion to read the book's first six chapters first. I was captivated through the first three chapters, and then somewhere in chapter 4 I began to get very weary with information overload. After putting the book down for a couple of days I decided to skip the rest and use what I needed to write the one regular expression I had need of. The book did successfully help me accomplish this, so I gave it 3 stars. Not only did it give me the information I needed that the online tutorials didn't, it also gave me the confidence I needed. For that, which I am grateful, I would have liked to have given it more stars. I think many of those in need of learning about regular expression could be well served by a "lite-edition" of this book. Perhaps someday when I have the time and the need I may try to wade through the rest of the book, but as it is now Mastering Regular Expressions took me far farther down the rabbit hole than I really needed or wanted to go.
If you need to get on top of Regular Expressions, I would recommend this book, however just be ready to be taken far deeper than the average coder probably needs to go.

An incredible book. Absolutely incredible. It will take 200 lines of your code and reduce it to 1 or 2 lines. It will open your mind to search and replace possibilities. Your life will change (just kidding). It's a great deep book.

However, I agree with the comment that one should not begin learning regex with this book. it's a little too advanced. Go on the internet, get an introduction. Or else, buy one of the introductory books on the subject first. But definitely get around to buying this book!

This book is seriously worth the money. I knew just enough regular expressions to get by, then I started reading this book and it has paid off already; saving me time on several long, arduous tasks.

The book is really well written, very interactive w/ quick, quizzing questions mixed throughout the chapters. The authors writing style is very effective and surprisingly entertaining.

If you don't know much about regular expressions or even if you think you do, purchase this book. It will be well worth it.

I have been in computer software developer over 7 years now and never really used regular expression until a year ago. True, you can live without it. But, with regular expression at hand, you climb up another level of programming. Code will be much concise and code research will be like a breeze.

Anyway, I didn't read this book entirely since later chapters explain intricacies and subtle differences of each specific language, e.g., java, perl, php, etc. It didn't take long to apply the knowledge I gained to real work and benefit. By the time I completed the first chapter, I already started to get rewards. My life is a lot easier now.

Even with only the first 3 chapters, this book is well worth its price. The author did superb job explaining what's going on behind the scene and guide you through the right way of constructing regular expressions for various situations. Of course, he will show you common pitfalls to avoid, too. Very detailed and comprehensive.

Highly recommended.

Before reading this book, I would have considered myself an intermediate regexer. After the first 2 chapters, I realized how novice I really was. Having only made it through 5 chapters of this book, I can't say enough about it. The detail and step-by-step analysis that Mr. Friedl takes to describe the regex matching process is the best I've ever seen. It's little things that make the analysis easy to follow -- like the brackets he uses to mark the regex, and the small triangle cursor to show where the engine is in the matching process. I continue to look forward to each new chapter. Thank you for a wonderful work of art.