I find myself using this book as a refernce almost every day. It is well written and easy to follow. I highly recommend it.

I bought this book after trying to learn Perl through another book (Perl for Bioinformatics). This book is definitely a better introduction to Perl than any other book I've seen. It is clear and concise enough and although it might be hard to finish it in 21 days, you can start coding your own scripts much before the end of the book. I am still on chapter 11 and I can program most of what I need with it (i.e parsers and simple bioinformatics applications). I recognize that there are a few typos on the book but if even Knuth's Art of Computer Programming have them why shouldn't Lemay's Teach Yourself Perl in 21 Days do the same?

Given what I said above, I must warn begginer programmers (like me) that Perl is not the best language for you to learn as your first one. It is a dirty scripting language which does the job and is most suitable for parsing files and formatting data but it has a lot of things which make it quite confusing initially (its context dependency for instance). If you want to learn something that will give a solid programming base you should start with something else (i.e. Java, Pascal, Ruby etc) which will probably be a little bit harder but will payoff later.

Teach Yourself Perl in 21 Days by Laura Lemay is sufficient for the beginner wanting to learn Perl, be it on Windows or a UNIX-based operating system. If Perl is your first programming language, then this book is a fairly good book to choose as a starting point. It teaches the basics of programming in Perl and moves quickly from that point onward.

However, while this approach introduced me to the language I found my ability to pace through the book as I normally would with other programming languages hindered by the author's organization. Unexplained code is used in almost all of the examples before you get to its respective chapter. While this approach may work for some and give cause for thinking, it gave me an unnecessary headache.

Don't get me wrong, it did teach me a good bit about Perl, it inspired me to install Debian Linux on my programming workstation, and left me to pursue Perl. Despite this, I turned to Learning Perl. I found Lemay's writing to be too verbose and the organization of the book a bit of a twister.

Overall, it can be summed up by the following pros/cons:

~ Pros
- Good introduction to Perl
- Independent of Operating System (Great for Windows users ready to Learn Perl and perhaps Migrate to Linux for programming purposes)
- Solid examples and references
- Covers more advanced topics later on

~ Cons
- Verbose
- Awkward structure. Things such as loops are constantly used in beginning examples without much of an explanation. If you don't' have any experience with programming, it will give you a headache. The sections on these devices come much later, and have a strange introduction as well.
- Frustrating at times when it shouldn't be (IE, having you use functions that you haven't learned, or haven't been mentioned, in an example for a particular chapter)

Additionally, I'd recommend picking up Learning Perl or using it instead. I picked up Teach Yourself Perl in 21 Days, learned what I could, and then fell in love with Learning Perl's concise, straight to the point chapters and examples (albeit with a fair amount of humor). If you're a Linux/UNIX user, you'll probably find Learning Perl a better catch, but for me, Teach Yourself Perl in 21 Days was the stepping stone to Linux and Learning Perl. Overall, I'm satisfied with my purchase.

If you want to start programming Perl in the shortest time possible, and have some programming background, you will benefit from reading Sam's Teach Yourself Perl in 24 Hours, which packs a lot of practical materials and emphasizes get-your-hands-dirty-immediately as well as uses a lot of code snippets to teach.

This "in 21 days" book, on the other hand, is better if you have more time to learn Perl. Each lesson takes 1-2 hours, if you already have some programming background, and longer if you don't. This book treats Perl more systematically and in more details than the "24 hours" book. It explains a lot of concepts, including hashes and modules, more clearly than the "24 hours" book. I recommend you do 2 or 3 lessons each day, because Perl is such a compact yet complicated language, that it's best to force yourself to learn it quickly, rather than slowly, because slow learning will make you forget things. Be sure to study the examples in the book until you understand every line of code.

This book is not helpful for the newbies. Not only do some of the scripts not work, but the way Perl is explained in this book, it just doesn't make enough sense. I learned more from online tutorials that were perhaps 3 pages long than I learned in 15 pages of one chapter of this book. I usually pick things up quite easily, so it must be the book that is confusing.

At least two of the script examples given in Chapters 1-8 had typos in them, and not enough explanation for someone that doesn't know much to figure out what. I am unfortunately going to have to give up on this book to learn Perl and turn to the internet... too bad I spent $35 for the book. I don't recommend this book to anyone except perhaps someone that already knows Perl.