Typographical Conventions

The following font conventions are used in this book:

Constant width

Used for method names, function names, variables, and attributes. It is also used for code examples.

Constant width bold

Used to indicate user input.

Constant width italic

Used to indicate a replaceable item in code (e.g., filename, where you are supposed to substitute an actual filename).

Italic

Used for filenames, URLs, hostnames, commands in text, important words on first mention, and emphasis.

[37]

At the start of an exercise’s text, we provide a (very rough) estimate of how many minutes you can expect to spend on that particular exercise.

Code Examples

This book is here to help you get your job done. You are invited to copy the code in the book and adapt it for your own needs. Rather than copying by hand, however, we encourage you to download the code from the book’s companion website. You do not need to contact us for permission unless you’re reproducing a significant portion of the code. For example, writing a program that uses several chunks of code from this book does not require permission. Selling or distributing examples from O’Reilly books does require permission. Answering a question by citing this book and quoting example code does not require permission. Incorporating a significant amount of example code from this book into your product’s documentation does require permission.

We appreciate, but do not require, attribution. An attribution usually includes the title, authors, publisher, and ISBN. For example: “Learning Perl, 8th edition, by Randal L. Schwartz, brian d foy, and Tom Phoenix (O’Reilly). Copyright 2021 Enhydra Services, LLC, 978-1-492-09495-1.” If you feel your use of code examples falls outside fair use or the permission given above, feel free to contact us at [email protected].

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History of This Book

For the curious, here’s how Randal tells the story of how this book came about:

After I had finished the first Programming perl book with Larry Wall (in 1991), I was approached by Taos Mountain Software in Silicon Valley to produce a training course. This included having me deliver the first dozen or so courses and train their staff to continue offering the course. I wrote the course for them¹ and delivered it for them as promised.

On the third or fourth delivery of that course (in late 1991), someone came up to me and said, “You know, I really like Programming perl, but the way the material is presented in this course is so much easier to follow—you oughta write a book like this course.” It sounded like an opportunity to me, so I started thinking about it.

I wrote to Tim O’Reilly with a proposal based on an outline that was similar to the course I was presenting for Taos—although I had rearranged and modified a few of the chapters based on observations in the classroom. I think that was my fastest proposal acceptance in history—I got a message from Tim within 15 minutes, saying “We’ve been waiting for you to pitch a second book—Programming perl is selling like gangbusters.” That started the effort over the next 18 months to finish the first edition of Learning Perl.

During that time, I was starting to see an opportunity to teach Perl classes outside Silicon Valley,² so I created a class based on the text I was writing for Learning Perl. I gave a dozen classes for various clients (including my primary contractor, Intel Oregon), and used the feedback to fine-tune the book draft even further.

The first edition hit the streets on the first day of November 1993,³ and became a smashing success, frequently even outpacing Programming perl book sales.

The back-cover jacket of the first book said “written by a leading Perl trainer.” Well, that became a self-fulfilling prophecy. Within a few months, I was starting to get email from all over the United States asking me to teach at their site. In the following seven years, my company became the leading worldwide on-site Perl training company, and I had personally racked up (literally) a million frequent-flier miles. It didn’t hurt that the web started taking off about then, and the webmasters and webmistresses picked Perl as the language of choice for content management, interaction through CGI, and maintenance.

For two years, I worked closely with Tom Phoenix in his role as lead trainer and content manager for Stonehenge, giving him charter to experiment with the “Llama” course by moving things around and breaking things up. When we had come up with what we thought was the best major revision of the course, I contacted O’Reilly and said, “It’s time for a new book!” And that became the third edition.

Two years after writing the third edition of the Llama, Tom and I decided it was time to push our follow-on “advanced” course out into the world as a book, for people writing programs that are “100 to 10,000 lines of code.” And together we created the first Alpaca book (Learning Perl Objects, References, and Modules), released in 2003.

But fellow instructor brian d foy had noticed that we could use some rewriting in both books, because our courseware still needed to track the changing needs of the typical student. So, he pitched the idea to O’Reilly to take on rewriting both the Llama and the Alpaca. This edition of the Llama reflects those changes. brian has really been the lead writer here, working with my occasional guidance, and has done a brilliant job of the usual “herding cats“ that a multiple-writer team generally feels like.

On December 18, 2007, the Perl 5 Porters released Perl 5.10, a significant new version of Perl with several new features. The previous version, 5.8, had focused on the underpinnings of Perl and its Unicode support. The latest version, starting from the stable 5.8 foundation, was able to add completely new features, some of which it borrowed from the development of Perl 6. Some of these features, such as named captures in regular expressions, are much better than the old ways of doing things, thus perfect for Perl beginners. We hadn’t thought about a fifth edition of this book, but Perl 5.10 was so much better that we couldn’t resist.

Since then, Perl has been under constant improvement and is keeping a regular release cycle. Each new Perl release has brought exciting new features, many of which programmers have wanted for years. As long as Perl keeps doing that, we’ll keep updating this book.

Changes from the Previous Edition

The text is updated for the latest version, Perl 5.34, and some of the code only works with that version. We note in the text when we are writing about a Perl 5.34 feature, and we mark those code sections with a special use statement that ensures you’re using the right version:

use v5.34; # this script requires Perl 5.34 or greater

If you don’t see that use v5.34 in a code example (or a similar statement with a different version), it should work all the way back to Perl 5.8. To see which version of Perl you have, try the -v command-line switch:

$ perl -v

In some examples, we’ll show a lower minimum Perl version because that’s all the program needs. For instance, say was introduced in Perl v5.10:

use v5.10;

say "Howdy, Fred!";

In most cases, we’ll probably forgo a new feature to make the examples work on as many versions of Perl as possible. That doesn’t mean you shouldn’t use the new features or that we don’t endorse them. We simply have a wide audience for this book.

We include Unicode examples and features where appropriate. If you haven’t started playing with Unicode, you may want to read our primer in Appendix C. You have to bite the bullet sometimes, so it might as well be now. You’ll see Unicode throughout the book, most notably in the chapters on scalars (Chapter 2), input/output (Chapter 5), and sorting (Chapter 14).

Here’s a quick summary of the updated or new things in this edition:

• We updated references to Perl 6 to call it by its new name, “Raku.”

• The search.cpan.org site was subsumed into MetaCPAN, so we removed references to the old site.

• ActiveState has discontinued PPM, its Perl Package Manager, so we’ve removed references to that.

Acknowledgments