正则表达式权威指南：Jeffrey Friedl的Mastering Regular Expressions

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"Jeffrey Friedl的著作《Mastering Regular Expressions》第三版是一本深入探讨正则表达式的权威书籍。作者Jeffrey E.F. Friedl通过本书详细讲解了正则表达式的概念、语法和应用，旨在帮助读者精通这一强大的文本处理工具。" 正则表达式，或简称为regex，是编程和文本处理中的核心概念，它是一种模式匹配语言，允许用户用简洁的语法来定义复杂的字符串匹配规则。在计算机科学中，正则表达式常用于数据验证、搜索、替换以及文本分析等任务。它们可以在各种编程语言（如JavaScript、Python、Java、Perl等）和工具（如grep、sed和许多文本编辑器）中使用。《Mastering Regular Expressions》第三版深入介绍了正则表达式的各个方面，包括基础的字符类、量词、分组、断言、反向引用、预查以及正则表达式引擎的工作原理。书中还涵盖了高级主题，如Unicode支持、回溯优化、条件表达式以及如何编写自己的正则表达式库。在第一版和第二版的基础上，第三版更新了与最新技术相关的资料，包括对新的正则表达式功能的支持，以及对各种编程环境中的实现差异的讨论。作者Jeffrey Friedl以其丰富的经验和深入的理解，为读者提供了大量实用的例子和技巧，帮助读者避免常见陷阱，提高使用正则表达式的效率和准确性。此外，本书还强调了正则表达式在实际问题中的应用，如网页抓取、数据清理、日志分析等，通过具体的案例让读者能够将理论知识转化为实际技能。书中的练习题和挑战也鼓励读者动手实践，巩固所学知识。《Mastering Regular Expressions》第三版是学习和提升正则表达式技能的宝贵资源，无论你是初学者还是经验丰富的开发者，都能从中受益匪浅。通过阅读本书，你将能够更有效地处理文本数据，解决各种复杂的数据匹配和处理问题。

xx Preface

The introduction elevates the absolute novice to “issue-aware” novice. Readers

with a fair amount of experience can feel free to skim the early chapters, but I par-

ticularly recommend Chapter 3 even for the grizzled expert.

•Chapter 1, Intr oduction to Regular Expressions,isgear ed toward the complete

novice. I introduce the concept of regular expressions using the widely avail-

able program egr ep,and offer my perspective on how to think regular expres-

sions, instilling a solid foundation for the advanced concepts presented in later

chapters. Even readers with former experience would do well to skim this ﬁrst

chapter.

•Chapter 2, Extended Introductory Examples,looks at real text processing in a

pr ogramming language that has regular-expr ession support. The additional

examples provide a basis for the detailed discussions of later chapters, and

show additional important thought processes behind crafting advanced regular

expr essions. To provide a feel for how to “speak in regular expressions,”this

chapter takes a problem requiring an advanced solution and shows ways to

solve it using two unrelated regular-expr ession–wielding tools.

•Chapter 3, Overview of Regular Expression Features and Flavors,provides an

overview of the wide range of regular expressions commonly found in tools

today. Due to their turbulent history, current commonly-used regular-expr es-

sion ﬂavors can differ greatly. This chapter also takes a look at a bit of the his-

tory and evolution of regular expressions and the programs that use them. The

end of this chapter also contains the “Guide to the Advanced Chapters.”This

guide is your road map to getting the most out of the advanced material that

follows.

TheDetails

Once you have the basics down, it’s time to investigate the how and the why.Like

the “teach a man to ﬁsh” parable, truly understanding the issues will allow you to

apply that knowledge whenever and wherever regular expressions arefound.

•Chapter 4, The Mechanics of Expression Processing,ratchets up the pace sev-

eral notches and begins the central coreofthis book. It looks at the important

inner workings of how regular expression engines really work from a practi-

cal point of view. Understanding the details of how regular expressions are

handled goes a very long way toward allowing you to master them.

•Chapter 5, Practical Regex Techniques,then puts that knowledge to high-level,

practical use. Common (but complex) problems areexplor ed in detail, all with

the aim of expanding and deepening your regular-expr ession experience.

2July 2006 02:01

•Chapter 6, Crafting an Efﬁcient Expression,looks at the real-life efﬁciency

ramiﬁcations of the regular expressions available to most programming lan-

guages. This chapter puts information detailed in Chapters 4 and 5 to use for

exploiting an engine’s strengths and stepping around its weaknesses.

Tool-Specific Infor mation

Once the lessons of Chapters 4, 5, and 6 areunder your belt, thereisusually little

to say about speciﬁc implementations. However,I’ve devoted an entirechapter to

each of four popular systems:

•Chapter 7, Perl,closely examines regular expressions in Perl, arguably the

most popular regular-expr ession–laden pr ogramming language in use today. It

has only four operators related to regular expressions, but their myriad of

options and special situations provides an extremely rich set of programming

options

—

and pitfalls. The very richness that allows the programmer to move

quickly from concept to program can be a mineﬁeld for the uninitiated. This

detailed chapter clears a path.

•Chapter 8, Java,looks in detail at the java.util.regex regular-expr ession

package, a standard part of the language since Java 1.4. The chapter’s primary

focus is on Java 1.5, but differ ences in both Java 1.4.2 and Java 1.6 arenoted.

•Chapter 9, .NET,isthe documentation for the .NET regular-expr ession library

that Microsoft neglected to provide. Whether using VB.NET,C#, C

,JScript,

VBscript, ECMAScript, or any of the other languages that use .NET components,

this chapter provides the details you need to employ .NET regular-expr essions

to the fullest.

•Chapter 10, PHP,provides a short introduction to the multiple regex engines

embedded within PHP,followed by a detailed look at the regex ﬂavor and API

of its preg regex suite, powered under the hood by the PCRE regex library.

Typog raphical Conventions

When doing (or talking about) detailed and complex text processing, being pre-

cise is important. The mereaddition or subtraction of a space can make a world of

dif ference, so I’ve used the following special conventions in typesetting this book:

• Aregular expression generally appears like

!this".Notice the thin corners

which ﬂag “this is a regular expression.”Literal text (such as that being

searched) generally appears like ‘this’. At times, I’ll leave offthe thin corners

or quotes when obviously unambiguous. Also, code snippets and screen shots

ar e always presented in their natural state, so the quotes and corners arenot

used in such cases.

Preface xxi

2July 2006 02:01

xxii Preface

• Iuse visually distinct ellipses within literal text and regular expressions. For

example [˙˙˙] repr esents aset of squarebrackets with unspeciﬁed contents,

while [...] would be a set containing three periods.

• Without special presentation, it is virtually impossible to know how many

spaces arebetween the letters in “a b”,sowhen spaces appear in regular

expr essions and selected literal text, they arepresented with the ‘

’symbol.

This way, it will be clear that thereare exactly four spaces in ‘

b’.

• Ialso use visual tab, newline, and carriage-retur n characters:

aspace character

2 atab character

1 anewline character

| acarriage-r eturncharacter

• At times, I use underlining or shade the background to highlight parts of literal

text or a regular expression. In this example the underline shows whereinthe

text the expression actually matches:

Because

!cat" matches ‘It

indicat

your

cat

is˙˙˙’instead of the

word ‘

cat’, we realize . . .

In this example the underlines highlight what has just been added to an

expr ession under discussion:

To make this useful, we can wrap

!Subject;Date" with parentheses,

and append a colon and a space. This yields

Subject;Date):

• This book is full of details and examples, so I’ve included over 1,200 cross ref-

er ences to help you get the most out of it. They often appear in the text in a

“☞123” notation, which means “see page 123.”For example, it might appear

like “ ...isdescribed in Table 8-2 (

☞

367).”

Exer cises

Occasionally, and particularly in the early chapters, I’ll pose a question to highlight

the importance of the concept under discussion. They’renot therejust to take up

space; I really do want you to try them beforecontinuing. Please. So as not to

dilute their importance, I’ve sprinkled only a few throughout the entirebook. They

also serve as checkpoints: if they take morethan a few moments, it’s probably

best to go over the relevant section again beforecontinuing on.

To help entice you to actually think about these questions as you read them, I’ve

made checking the answers a breeze: just turnthe page. Answers to questions

marked with

❖

ar e always found by turning just one page. This way, they’reout

of sight while you think about the answer,but arewithin easy reach.

2July 2006 02:01

xxiv Preface

Personal Comments and

Acknowledgments

Writing the ﬁrst edition of this book was a grueling task that took two and a half

years and the help of many people. After the toll it took on my health and sanity, I

pr omised that I’d never put myself through such an experience again.

Ihave many people to thank in helping me break that promise. Foremost is my

wife, Fumie. If you ﬁnd this book useful, thank her; without her support and

understanding, I’d have neither the strength nor sanity to undertake a task as ardu-

ous as the research, writing, and production of a book like this.

While researching and writing this book, many people helped educate me on lan-

guages or systems I didn’t know, and morestill reviewed and corrected drafts as

the manuscripts developed.

In particular,I’d like to thank my brother,Stephen Friedl, for his meticulous and

detailed reviews along the way. (Besides being an excellent technical reviewer,

he’s also an accomplished writer,known for his well-researched “Tech Tips,”avail-

able at http://www.unixwiz.net/)

I’d also like to thank Zak Greant, Ian Morse, Philip Hazel, Stuart Gill, William F.

Maton, and my editor,Andy Oram.

Special thanks for providing an insider’s look at Java go to Mike “madbot”

McCloskey (formerly at Sun Microsystems, now at Google), and Mark Reinhold

and Dr.Clif f Click, both of Sun Microsystems. For .NET insight, I’d like to thank

Micr osoft’s David Gutierrez, Kit George, and Ryan Byington. I thank Andrei

Zmievski of Yahoo! for providing insights into PHP.

I’d like to thank Dr.Ken Lunde of Adobe Systems, who created custom characters

and fonts for a number of the typographical aspects of this book. The Japanese

characters arefromAdobe Systems’ Heisei Mincho W3 typeface, while the Korean

is from the Korean Ministry of Cultureand Sports Munhwa typeface. It’s also Ken

who originally gave me the guiding principle that governs my writing: “you do the

research so your readers don’t have to.”

For help in setting up the server for http://r egex.info,I’d like to thank Jeffr ey

Papen and Peak Web Hosting (http://www.PeakWebhosting.com/).

2July 2006 02:01

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