掌握Perl编程：第七版

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"Learning Perl 7th edition 是一本专为初学者设计的Perl编程书籍，由Randal L. Schwartz、brian d foy和Tom Phoenix合著。这本书紧贴作者们自1991年以来教授的Perl入门课程，并涵盖了Perl语言至5.24版本的最新变化。Perl是一种多平台适用的编程语言，适用于各种任务，从小规模的修复到完整的Web应用程序。本书旨在教你基础，让你能够编写最多128行的程序，这与当前使用的大多数Perl程序的大小相当。书中每章都包含练习，帮助巩固学习。除了教授如何用Perl编程，它更致力于培养读者成为真正的Perl程序员。本书涵盖的主题包括：数据和变量类型、子程序、文件操作、正则表达式、字符串处理（包括Unicode）、列表和排序、进程管理、智能匹配以及第三方模块的使用。" 在"Learning Perl 7th edition"中，读者将深入理解Perl的基础和核心概念： 1. **Perl数据和变量类型**：Perl支持多种数据类型，如标量（数字或字符串）、数组、哈希和引用。变量在Perl中以$、@、%或&符号开头，分别对应标量、数组、哈希和函数。 2. **子程序（Subroutines）**：Perl中的子程序允许将代码块封装起来，以便在程序的不同部分重复使用。它们类似于其他语言中的函数，可以接收参数并返回值。 3. **文件操作**：Perl提供了丰富的文件处理功能，包括打开、关闭、读取和写入文件，以及文件和目录的创建和删除。 4. **正则表达式**：Perl是正则表达式的强大工具，允许进行复杂的文本模式匹配和替换，是处理文本数据时不可或缺的工具。 5. **字符串处理（包括Unicode）**：Perl支持字符串的广泛操作，包括拼接、截断、查找和替换。此外，Perl对Unicode的支持使得处理多种字符集成为可能。 6. **列表和排序**：Perl的数组（列表）提供了处理一系列元素的方法，而排序函数可以按指定顺序排列数组元素。 7. **进程管理**：Perl提供了进程控制功能，如fork、exec和wait，可以创建和管理子进程。 8. **智能匹配**：Perl 5.10引入了智能匹配运算符，可以用于比较不同类型的值，简化了对象和模式的比较。 9. **使用第三方模块**：Perl拥有丰富的CPAN（ Comprehensive Perl Archive Network）库，包含数万个模块，覆盖各种领域。书中的这部分将教导读者如何安装和使用这些模块来扩展Perl的功能。通过阅读和实践"Learning Perl 7th edition"中的内容，读者将能够熟练掌握Perl语言，从而轻松完成日常编程任务，并具备解决复杂问题的能力。无论是系统管理员、程序员还是Web开发者，都能从这本书中受益匪浅。

1 In the contract, I retained the rights to the exercises, hoping someday to reuse them in some other way, like in

the magazine columns I was writing at the time. The exercises are the only things that leapt from the Taos

course to the book.

O’Reilly Media, Inc.

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We have a web page for the book, where we’ll list examples, errata, and any additional

information. It also offers a downloadable set of text files (and a couple of Perl pro‐

grams) that are useful, but not required, when doing some of the exercises. You can

access this page at http://www.learning-perl.com or go to the O’Reilly page.

To comment or ask technical questions about this book, send email to

info@oreilly.com.

For more information about our books, courses, conferences, and news, see our web‐

site at http://www.oreilly.com.

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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 them

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 pre‐

sented 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 pro‐

xiv | Preface

2 My Taos contract had a non-compete clause, so I had to stay out of Silicon Valley with any similar courses,

which I respected for many years.

3 I remember that date very well, because it was also the day I was arrested at my home for computer-related

activities around my Intel contract, a series of felony charges for which I was later convicted.

posal 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,

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 Ore‐

gon), 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,

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 com‐

pany, 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 webmis‐

tresses 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 con‐

tent 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.

Preface | xv

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 bor‐

rowed from the development of Perl 6. Some of these features, such as named cap‐

tures 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 5.24, and some of the code only works

with that version. We note in the text when we are writing about a Perl 5.24 feature,

and we mark those code sections with a special use statement that ensures you’re

using the right version:

use v5.24; # this script requires Perl 5.24 or greater

If you don’t see that use v5.24 in a code example (or a similar statement with a dif‐

ferent 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 fea‐

tures 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 sometime, 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 (Chap‐

ter 5), and sorting (Chapter 14).

xvi | Preface

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

• An appendix on experimental features (Appendix D)

• More Windows examples where appropriate

• Hexadecimal floating-point literals (v5.22) in Chapter 2

• The experimental but very exciting subroutine signatures (v5.20) in Chapter 4

•

The more-secure double diamond line input operator (v5.22) in Chapter 5

• Many updates to regular expressions and match operator flags in Chapters 7

through 9

• Use Time::Moment over DateTime as an example in Chapter 11

• The experimental bitwise string operators in Chapter 12

• Key-value slices (v5.20) in Chapter 16

Acknowledgments

From Randal

I want to thank the Stonehenge trainers past and present (Joseph Hall, Tom Phoenix,

Chip Salzenberg, brian d foy, and Tad McClellan) for their willingness to go out and

teach in front of classrooms week after week and to come back with their notes about

what’s working (and what’s not), so we could fine-tune the material for this book. I

especially want to single out my coauthor and business associate, Tom Phoenix, for

having spent many, many hours working to improve Stonehenge’s Llama course and

to provide the wonderful core text for most of this book. And brian d foy for being

the lead writer beginning with the fourth edition, and taking that eternal to-do item

out of my inbox so that it would finally happen.

I also want to thank everyone at O’Reilly, especially our very patient editor and over‐

seer for previous editions, Allison Randal (no relation, but she has a nicely spelled last

name), current editor Simon St. Laurent, and Tim O’Reilly himself for taking a

chance on me in the first place with the Camel and Llama books.

I am also absolutely indebted to the thousands of people who have purchased the past

editions of the Llama so that I could use the money to stay “off the streets and out of

jail,” and to those students in my classrooms who have trained me to be a better

trainer, and to the stunning array of Fortune 1000 clients who have purchased our

classes in the past and will continue to do so into the future.

As always, a special thanks to Lyle and Jack, for teaching me nearly everything I know

about writing. I won’t ever forget you guys.

Preface | xvii

From brian

I have to thank Randal first, since I learned Perl from the first edition of this book,

and then had to learn it again when he asked me to start teaching for Stonehenge in

1998. Teaching is often the best way to learn. Since then, Randal has mentored me not

only in Perl but several other things he thought I needed to learn—like the time he

decided that we could use Smalltalk instead of Perl for a demonstration at a web con‐

ference. I’m always amazed at the breadth of his knowledge. He’s the one who told me

to start writing about Perl. Now I’m helping out on the book where I started. I’m hon‐

ored, Randal.

I probably only actually saw Tom Phoenix for less than two weeks in the entire time I

worked for Stonehenge, but I had been teaching his version of Stonehenge’s Learning

Perl course for years. That version turned into the third edition of this book. By

teaching Tom’s new version, I found new ways to explain almost everything, and

learned even more corners of Perl.

When I convinced Randal that I should help out on the Llama update, I was anointed

as the maker of the proposal to the publisher, the keeper of the outline, and the ver‐

sion control wrangler. Our editor, Allison Randal, helped me get all of those set up

and endured my frequent emails without complaining. After Allison went on to other

things, Simon St. Laurent has been extremely helpful in the role of editor and inside

guy at O’Reilly, patiently waiting for the right phase of the moon to suggest another

update.

From Tom

I’ve got to echo Randal’s thanks to everyone at O’Reilly. For the third edition of this

book, Linda Mui was our editor, and I still thank her, for her patience in pointing out

which jokes and footnotes were most excessive, while pointing out that she is in no

way to blame for the ones that remain. Both she and Randal have guided me through

the process of writing, and I am grateful. In a previous edition, Allison Randal took

charge; now Simon St. Laurent has become the editor. My thanks go to each of them

in recognition of their unique contributions.

And another echo with regard to Randal and the other Stonehenge trainers, who

hardly ever complained when I unexpectedly updated the course materials to try out

a new teaching technique. You folks have contributed many different viewpoints on

teaching methods that I would never have seen.

For many years, I worked at the Oregon Museum of Science and Industry (OMSI),

and I’d like to thank the folks there for letting me hone my teaching skills as I learned

to build a joke or two into every activity, explosion, or dissection.

To the many folks on Usenet who have given me your appreciation and encourage‐

ment for my contributions there, thanks. As always, I hope this helps.

xviii | Preface

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