精通正则表达式第三版精华解读

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"Mastering Regular Expressions 3rd Edition" 是一本由 Jeffrey E.F. Friedl 撰写的关于正则表达式的权威书籍，适合代码复制和学习。在信息技术领域，正则表达式（Regular Expressions，简称 RegExp）是用于模式匹配和文本处理的强大工具。本书“精通正则表达式”第三版深入浅出地介绍了这一概念，帮助读者掌握这一技能。作者 Jeffrey E.F. Friedl 是正则表达式领域的专家，他的著作提供了详尽的教程和实用指南，适合初学者和有经验的开发者。本书的内容可能涵盖了以下几个主要方面： 1. 基础概念：书中首先会介绍正则表达式的最基本元素，如字符集、通配符、重复和位置匹配符号，帮助读者构建对正则表达式的基础理解。 2. 元字符与转义：详细解释元字符（如 ., *, +, ?, ^, $, \ 等）的功能和用法，以及如何通过转义来处理特殊字符。 3. 分组与捕获：讲解如何使用括号进行分组，以便重复或捕获子模式，以及非捕获组和命名组的概念。 4. 分支条件与环视断言：介绍如何使用竖线 | 表示选择，以及前向和后向环视断言（如 look-ahead 和 look-behind）来精确匹配模式。 5. 替换与反向引用：探讨如何使用正则表达式进行字符串替换，并解释反向引用在替换过程中的应用。 6. 正则表达式引擎的差异：由于不同的编程语言和工具对正则表达式的支持程度不同，本书可能讨论了各种实现之间的差异，如Perl、Java、JavaScript、.NET等。 7. 高级技巧与最佳实践：提供高级用法，如回溯控制、预查、条件表达式等，并给出实际问题的解决方案和优化建议。 8. 实例解析：通过大量实例和案例研究，帮助读者解决实际工作中遇到的问题，提升对正则表达式的运用能力。 9. 性能与效率：讨论编写高效正则表达式的重要性，以及如何避免常见的性能陷阱。 10. 调试与测试工具：介绍如何利用工具（如regex tester）进行正则表达式的测试和调试。这本权威书籍不仅是学习正则表达式的理想教材，也是开发者案头必备的参考书，可以帮助读者从新手到专家，逐步提升在文本处理和数据提取方面的技能。无论是Web开发、数据分析还是系统管理，熟练掌握正则表达式都将极大地提高工作效率。

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.

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•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

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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.

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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/).

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