精通Perl编程：实践与进阶指南

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"Mastering Perl" 是一本旨在帮助读者掌握Perl编程高级技巧的书籍，它继 "Learning Perl" 和 "Intermediate Perl" 后，构成了一个完整的Perl学习系列。这本书不仅仅是一堆巧妙的技巧集合，而是通过讲解如何解决调试、维护、配置等实际编程问题，引导读者理解如何将Perl应用于实际工作中，提升到能够解决问题或找到问题答案的水平。书中涵盖了Perl编程的核心概念，包括但不限于模块设计、错误处理、性能优化和代码重构。作者深入探讨了如何写出可维护、可扩展的Perl代码，这对于任何希望在Perl领域深入发展的程序员来说都是至关重要的。此外，书中还讨论了如何利用Perl进行系统集成和自动化，以及如何与现有系统进行有效交互。 "Mastering Perl" 提供了丰富的实例，帮助读者理解和应用各种Perl编程策略。它鼓励读者采用最佳实践，比如模块化设计、文档编写和测试驱动开发，以提高代码质量和可读性。同时，书中还会介绍一些先进的Perl特性，如正则表达式的高级用法、对象导向编程以及并发和异步编程。为了进一步扩展学习，读者可以参考O'Reilly出版社提供的其他Perl相关资源，如 "Advanced Perl Programming" 进行深入研究，或者阅读 "Intermediate Perl" 来巩固基础。此外，"Perl Best Practices" 提供了关于编写整洁、规范代码的指导，而 "Perl Testing: A Developer's Notebook" 则专注于测试策略和工具。O'Reilly的 "Perl CD Bookshelf" 和 "Programming Perl" 也是Perl学习者的宝贵资料库。访问 hacks.oreilly.com，读者可以在社区网站上与其他开发者交流，分享他们关于Perl的技巧和工具。perl.oreilly.com 提供了O'Reilly所有Perl相关书籍的目录，包括样本章节和代码示例，是查找Perl技术信息的好去处。Perl.com是Perl社区的中心站点，是了解Perl最新动态的理想起点。参加O'Reilly组织的会议和活动（conferences.oreilly.com），可以接触到最新的工具和系统，学习如何将创新者的知识转化为实战技能。Safari Bookshelf在线参考图书馆（safari.oreilly.com）提供了一个全面的电子书库，方便读者随时随地查阅Perl和其他技术的相关资料。 "Mastering Perl" 是一本全面且深入的Perl编程指南，不仅适合有一定基础的Perl程序员提升技能，也对那些寻求成为Perl专家的开发者具有极高的参考价值。通过学习本书，读者将能够更好地驾驭Perl，解决复杂的问题，并在日常工作中更加得心应手。

CHAPTER 1

Introduction: Becoming a Master

This book isn’t going to make you a Perl master; you have to do that for yourself by

programming a lot of Perl, trying a lot of new things, and making a lot of mistakes. I’m

going to help you get on the right path. The road to mastery is one of self-reliance and

independence. As a Perl master, you’ll be able to answer your own questions as well as

those of others.

In the golden age of guilds, craftsmen followed a certain path, both literally and figu-

ratively, as they mastered their craft. They started as apprentices and would do the

boring bits of work until they had enough skill to become the more trusted journeymen.

The journeyman had greater responsibility but still worked under a recognized master.

When he had learned enough of the craft, the journeyman would produce a “master

work” to prove his skill. If other masters deemed it adequately masterful, the journey-

man became a recognized master himself.

The journeymen and masters also traveled (although people disagree on whether that’s

where the “journey” part of the name came from) to other masters, where they would

learn new techniques and skills. Each master knew things the others didn’t, perhaps

deliberately guarding secret methods, or knew it in a different way. Part of a

journeyman’s education was learning from more than one master.

Interactions with other masters and journeymen continued the master’s education. He

learned from those masters with more experience and learned from himself as he taught

journeymen, who also taught him because they brought skills they learned from other

masters.

The path an apprentice followed affected what he learned. An apprentice who studied

with more masters was exposed to many more perspectives and ways of teaching, all

of which he could roll into his own way of doing things. Odd teachings from one master

could be exposed by another, giving the apprentice a balanced view on things. Addi-

tionally, although the apprentice might be studying to be a carpenter or a mason,

different masters applied those skills to different goals, giving the apprentice a chance

to learn different applications and ways of doing things.

Unfortunately, we don’t operate under the guild system. Most Perl programmers learn

Perl on their own (I’m sad to say, as a Perl instructor), program on their own, and never

get the advantage of a mentor. That’s how I started. I bought the first edition of Learning

Perl and worked through it on my own. I was the only person I knew who knew what

Perl was, although I’d seen it around a couple of times. Most people used what others

had left behind. Soon after that, I discovered comp.lang.perl.misc and started answer-

ing any question that I could. It was like self-assigned homework. My skills improved

and I got almost instantaneous feedback, good and bad, and I learned even more Perl.

I ended up with a job that allowed me to program Perl all day, but I was the only person

in the company doing that. I kept up my homework on comp.lang.perl.misc.

I eventually caught the eye of Randal Schwartz, who took me under his wing and started

my Perl apprenticeship. He invited me to become a Perl instructor with Stonehenge

Consulting Services, and then my real Perl education began. Teaching, meaning figur-

ing out what you know and how to explain it to others, is the best way to learn a subject.

After a while of doing that, I started writing about Perl, which is close to teaching,

although with correct grammar (mostly) and an editor to correct mistakes.

That presents a problem for Mastering Perl, which I designed to be the third book of a

trilogy starting with Learning Perl and Intermediate Perl, both of which I’ve had a hand

in. Each of those are about 300 pages, and that’s what I’m limited to here. How do I

encapsulate the years of my experience in such a slim book?

In short, I can’t. I’ll teach you what I think you should know, but you’ll also have to

learn from other sources. As with the old masters, you can’t just listen to one person.

You need to find other masters, too, and that’s also the great thing about Perl: you can

do things in so many different ways. Some of these masters have written very good

books, from this publisher and others, so I’m not going to duplicate those topics here,

as I discuss in a moment.

What It Means to Be a Master

This book takes a different tone from Learning Perl and Intermediate Perl, which we

designed as tutorial books. Those mostly cover the details of the Perl language and only

a little on the practice of programming. Mastering Perl, however, puts more responsi-

bility on you, the reader.

Now that you’ve made it this far in Perl, you’re working on your ability to answer your

own questions and figure out things on your own, even if that’s a bit more work than

simply asking someone. The very act of doing it yourself builds your experience as well

as not annoying your coworkers.

Although I don’t cover other languages in this book, like Advanced Perl Program-

ming, First Edition, by Sriram Srinivasan (O’Reilly) and Mastering Regular Expres-

sions by Jeffrey Friedl (O’Reilly) do, you should learn some other languages. This

2 | Chapter 1: Introduction: Becoming a Master

informs your Perl knowledge and gives you new perspectives, some that make you

appreciate Perl more and others that help you understand its limitations.

And, as a master, you will run into Perl’s limitations. I like to say that if you don’t have

a list of five things you hate about Perl and the facts to back them up, you probably

haven’t done enough Perl. It’s not really Perl’s fault. You’ll get that with any language.

The mastery comes in by knowing these things and still choosing Perl because its

strengths outweigh the weakness for your application. You’re a master because you

know both sides of the problem and can make an informed choice that you can explain

to others.

All of that means that becoming a master involves work, reading, and talking to other

people. The more you do, the more you learn. There’s no shortcut to mastery. You may

be able to learn the syntax quickly, as in any other language, but that will be the tiniest

portion of your experience. Now that you know most of Perl, you’ll probably spend

your time reading some of the “meta”-programming books that discuss the practice of

programming rather than just slinging syntax. Those books will probably use a lan-

guage that’s not Perl, but I’ve already said you need to learn some other languages, if

only to be able to read these books. As a master, you’re always learning.

Becoming a master involves understanding more than you need to, doing quite a bit of

work on your own, and learning as much as you can from the experience of others. It’s

not just about the code you write, because you have to deal with the code from many

other authors too.

It may sound difficult, but that’s how you become a master. It’s worth it, so don’t give

up. Good luck!

Who Should Read This Book

I wrote this book as a successor to Intermediate Perl, which covered the basics of ref-

erences, objects, and modules. I’ll assume that you already know and feel comfortable

with those features. Where possible, I make references to Intermediate Perl in case you

need to refresh your skills on a topic.

If you’re coming directly from another language and haven’t used Perl yet, or have only

used it lightly, you might want to skim Learning Perl and Intermediate Perl to get the

basics of the language. Still, you might not recognize some of the idioms that come with

experience and practice. I don’t want to tell you not to buy this book (hey, I need to

pay my mortgage!), but you might not get the full value I intend, at least not right away.

How to Read This Book

I’m not writing a third volume of “Yet More Perl Features.” I want to teach you how

to learn Perl on your own. I’m setting you on your own path to mastery, and as an

apprentice, you’ll need to do some work on your own. Sometimes this means I’ll show

Who Should Read This Book | 3

you where in the Perl documentation to get the answers (meaning I can use the saved

space to talk about other topics).

What Should You Know Already?

I’ll presume that you already know everything that we covered in Learning Perl and

Intermediate Perl. By we, I mean the Stonehenge Consulting Services crew and best-

selling Perl coauthors Randal Schwartz, Tom Phoenix, and me.

Most importantly, you should know these subjects, each of which implies knowledge

of other subjects:

• Using Perl modules

• Writing Perl modules

• References to variables, subroutines, and filehandles

• Basic regular expression syntax and workings

• Object-oriented Perl

If I want to discuss something not in either of those books, I’ll explain it in a bit more

depth. Even if we did cover it in the previous books, I might cover it again just because

it’s that important.

What I Cover

After learning the basic syntax of Perl in Learning Perl and the basics of modules and

team programming in Intermediate Perl, the next thing you need to learn are the idioms

of Perl and the integration of the skills that you already have to create robust and

scalable applications that other people can use without your help.

I’ll cover some subjects you’ve seen in those two books, but in more depth. As we said

in Learning Perl, we sometimes told white lies to simplify the details and to get you

going as soon as possible without getting bogged down. Now it’s time to get a bit dirty

in the bogs.

Don’t mistake my coverage of a subject for an endorsement, though. There are millions

of Perl programmers in the world, and each has her own way of doing things. Part of

becoming a Perl master involves reading quite a bit of Perl even if you wouldn’t write

that Perl yourself. I’ll endeavor to tell you when I think you shouldn’t do something,

but that’s really just my opinion. As you strive to be a good programmer, you’ll need

to know more than you’ll use. Sometimes I’ll show things I don’t want you to use, but

I know you’ll see in code from other people. Oh well, it’s not a perfect world.

Not all programming is about adding or adjusting features in code. Sometimes it’s

pulling code apart to inspect it and watch it do its magic. Other times it’s about getting

rid of code that you don’t need. The practice of programming is more than creating

4 | Chapter 1: Introduction: Becoming a Master

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