Rating:  - Perfect book for taking your Perl skills to the next level
In the world of Perl there was once only the 'camel book,' held in perhaps as much reverence as 'K & R' among C programmers. It certainly appealed to roughly the same audience, those who wanted a short, sharp introduction to a programming language. It was with a problem that needed solving and a copy of the camel book that I started as a Perl programmer.
Then for those that wanted a introduction to Perl and programming Randal L. Schwartz wrote Learning Perl, a book that has arguably become the definitive textbook for teaching Perl. The one weakness was that it left off before really getting to the guts of building large, complex projects in Perl. It did not cover classes, objects, breaking your code up into pieces or the more arcane aspects of variables, references. For this we had to resort to the last few chapters of the 'camel book' and I, for one, have never really been totally comfortable at this end of the language; when I'm reading someone else's code it might take a couple of reads to fully understand the process.
Now this weakness has been well and truly addressed. Schwartz, with Tom Phoenix, has written "Learning Perl Objects, References & Modules", a volume that takes the same steady approach to teaching you the more advanced topics as the earlier 'Learning Perl'. Schwartz has spent the years since writing 'Learning Perl' teaching and writing. You can tell, this is a superbly written book, not that 'Learning Perl' wasn't well written; it's just that this volume is far better.
The Guts
The book starts with a chapter on building larger programs that covers @INC, eval, do and require before discussing packages and scope. It then has several chapters on references that explains in well understandable fashion and increasing complexity all the ins and outs of references including dereferencing, nested references, references to subroutines and references to anonymous data before a final chapter on references that gives you some incredibly useful tricks such as sorting and recursively defining complex data.
The book continues with three chapters that give you a solid grounding in Perl objects. Here Schwartz has assumed that you know at least a little about object oriented programming, some may feel the need for more explanation of concepts might be required, but if you've had any experience in OOP before then the clear examples and descriptions here are probably all you want.
Modules are not as well covered, with only a single chapter, but it is hard to think of anything left out, it covers using them and building your own so well that it left me wondering what all the fuss was about, "seems obvious to me." The book concludes with chapters on building a distribution out of your module, testing it using make test (with Test::Harness), Test::Simple and Test::More before a chapter telling you how to contribute to CPAN.
Each chapter of the book concludes with a number of small exercises, designed to be done in just a few minutes, that cement the learning of the previous chapter. The answers to these are at the end of the book.
Conclusion
Once I'd finished I felt I had a much more solid grounding in Perl, certainly I was much better able to understand another programmer's code that dealt with such things as subroutine references and some complex data structures. While the subject matter of this book is almost entirely covered in 'Programming Perl' the tutorial aspects of this book made it much easier going. The style would be familiar to anyone who has read 'Learning Perl', light without being frivolous and extremely well written, Schwartz seems a master at reducing complexity to manageable bites.
This book is deceptively easy to follow, each new idea built onto earlier ones, each new language concept introduced in an easy manner. The writing is excellent, it's hard to explain why I appreciated it so much. That may be the reason, the writing isn't forced or heavy or too light or obvious. It just allows the solid material of the book to shine through. Go to the ubiquitous O'Reilly website and grab the example chapter (the site also has a few Errata, the Table of Contents and the code from the book) and give it a look.
I think this may well become a classic, I may well in ten years time talk of Schwartz's books with the same awe I now talk of Brian Kernighan's. I'll certainly eagerly await his next book and keep this one close until it comes. Oh, and Randal, how about 'Software Tools for Perl Programmers'?
Rating:  - Good for intermediate perl programmers
To me, this book seemed like two books:
1) Shared Libraries, References, Data Structures, Scoping, and other things in perl. -- For internmediate programmers.
2) OO Perl, Distributions, and Testing in Perl - Step-by-Step - For advanced perl programmers who aspire to be wizards.
For me, part 1 was mostly review. Part 2 is good stuff, but it's not very deep. You could call it "a gentle introduction to OO"
My conclusion: The earlier in your career you read this book, the better. If the topics in #1 or #2 are "new" to you, go buy the book. Seriously. The comments on h2xs and the design patterns that schwartz sets up -alone- make it worth the price.
Rating: - perl book you should/must get
perl must-have's:
- camel,
- Hall/Schwartz: effective
- Friedl: Reg Ex
Should-have:
- Conway OO Perl (all 4 Manning perl titles are superb)
- Brown debuggin perl OR scott/wright Perl debugged
- Learning Python & Ruby pickax (so you know what's out there)
I'm not sure which list this fits on, but it'll save you a huge amount of time learning 3 topics over deciphering camel or Perl in Nutshell. Conway ties for best OO intro ever (w/Booch, of ~8 books I've looked at) This book is more of a survey of OO, data structs & mods in familiar llama style: Hand-holding at first, then they accelerate & things get dense pretty quick. Just enough example code to illustrate, there's no big app that gets worked up thru the book. So if you wanna master perl obj model, and approach problems w/tools like java, scheme, & (ahem) python/ruby developers have, get both books.
And ask OReilly to put this on the next update of PERL CD bookshelf.
Rating: - A Fabulous Sequel to 'Learning Perl'
Merlyn (as Randal Schwartz is known in Perl circles) is a fantastic author, and has written some of the most influential books on Perl available. For this book, he teamed up with his buddy and co-worker Tom Phoenix, who is another Perl luminary.
Picking up where they left off with their book 'Learning Perl' Randal and Tom plunge ahead into more advanced topics in Perl, giving you the reader in-depth knowledge in how to take Perl from small projects into large.
The writing is humorous, and easy to read, the examples are top-notch, and the knowledge is spot on.
If you're already familiar with Perl, and you're looking to take the next step forward, this is the book for you.
Kudos to the authors.
Rating: - Learning more Perl (sequel to "Learning Perl")
"Learning Perl Objects, References and Modules " is the sequel to "Learning Perl". It starts of where "Learning Perl" finished. In "Learning Perl" I learned how to write Perl programs. In "Learning Perl Objects" I learned how to write better and bigger Perl programs. The audience of this book is the advanced Perl Programmer that wants to improve his Perl knowledge in the area of OO programming.
If you want to use Perl's OO functions, you have to know a lot about references and modules / packages (an OO package is just a normal package that is called in OO fashion). The first couple of chapters (chapter 1-7) talk about these basics of Perl OO programming that can (and should) be used even without using OO. I love chapter 5 about complex data structures. The chapters 8-11 describe the Perl OO implementation. Further Meta information about how to program packages, CPAN and testing is provided in the chapters 12-15.
The setup of the book is didactically very good and the nicely "incremental". You can see that the authors developed this book out of courses that they have held and improved for a long time. Because the book provides a nice stepwise introduction into the subject, one should read it from beginning to end. To really practice the newly learned skills, Tom and Randal provide some example exercises (with solutions in the appendix) at the end of every chapter.
Although I am not a native English speaker, I found the book very readable and humorous. Again this is another O'Reilly book that presents a possibly dry subject in a very accessible way. Even though the explanations are very good, be prepared to read some chapters twice (or more) to get your "aha" moment.
Coming from a C++ background I still find it strange that Perl needs so little additional syntax for OO programming. This has of course some (little) disadvantages. Some things like calling abstract methods and class methods (or rather errors calling these methods) are not enforced at compile time but can be enforced at runtime (if you want). Tom and Randal explain this in their book of course (and hopefully I will not forget to implement this in my modules).
There is one great downside of this book: I would have loved it to be longer. This book has about 180 effective pages (plus appendix, index, foreword), which makes it a rather fast read compared to some of the "normal" IT brick stones.
"Learning Perl Objects" is an extraordinary good introductory book into advanced Perl programming with references, modules and objects. If you have liked "Learning Perl" and you want to proceed on your path to Perl mastery, you will love this book.
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