正则表达式入门指南

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"Introducing Regular Expressions" 是一本由 Michael Fitzgerald 撰写的书籍，于2012年7月出版。这本书主要介绍的是正则表达式这一编程和文本处理中的强大工具。正则表达式（Regular Expressions）是计算机科学领域的一个重要概念，它是一种模式匹配语言，用于在文本中查找、替换或提取特定模式的字符串。它们被广泛应用于各种编程语言，如JavaScript、Python、Java等，以及许多文本编辑器和搜索引擎中。在这本书中，作者Michael Fitzgerald很可能深入浅出地讲解了正则表达式的基础知识，包括但不限于以下内容： 1. **基础语法**：正则表达式的基本构成元素，如字符类（[]）、量词（*、+、?、{n,m}）、分组（()）、锚点（^、$）、转义字符（\）等。 2. **匹配机制**：如何使用正则表达式进行匹配，包括贪婪与非贪婪匹配、前后查找（^和$的特殊用法）、零宽断言（如(?=)和(?!)]。 3. **高级特性**：可能涵盖条件表达式、后向引用、环视等复杂正则表达式构造。 4. **实际应用**：书中可能会通过实例展示正则表达式在文本处理、数据验证、日志分析等方面的应用。 5. **常见问题与陷阱**：解决在编写和调试正则表达式时可能遇到的问题，以及避免常见的错误和误解。 6. **不同的正则表达式引擎**：由于不同编程语言实现的正则表达式引擎可能有差异，书里可能介绍了如何在不同环境（如Perl、JavaScript、PCRE等）下使用正则表达式。 7. **实践项目**：通过实践项目来巩固所学，帮助读者更好地理解和运用正则表达式。这本书的出版方是O'Reilly Media，他们出版的技术书籍以内容专业、质量高而闻名。编辑Simon St. Laurent、生产编辑Holly Bauer等人对书籍的制作过程进行了监督和贡献，确保了内容的准确性和专业性。对于想深入学习和掌握正则表达式的读者来说，这本书是一个很好的起点。无论是初学者还是有一定经验的开发者，都能从中获取有价值的信息，并提升自己在文本处理和数据分析方面的技能。通过阅读本书，你可以学会如何利用正则表达式更高效地处理和解析大量文本数据，提升工作效率。

Chapter 10 shows you a slightly more sophisticated regular expression

for a phone number, but the one above is sufficient for the purposes of

this chapter.

If you don’t get how that all works yet, don’t worry: I’ll explain the whole expression

a little at a time in this chapter. If you will just follow the examples (and those through-

out the book, for that matter), writing regular expressions will soon become second

nature to you. Ready to find out for yourself?

I at times represent Unicode characters in this book using their code point—a four-

digit, hexadecimal (base 16) number. These code points are shown in the form

U+0000. U+002E, for example, represents the code point for a full stop or period (.).

Getting Started with Regexpal

First let me introduce you to the Regexpal website at http://www.regexpal.com. Open

the site up in a browser, such as Google Chrome or Mozilla Firefox. You can see what

the site looks like in Figure 1-1.

You can see that there is a text area near the top, and a larger text area below that. The

top text box is for entering regular expressions, and the bottom one holds the subject

or target text. The target text is the text or set of strings that you want to match.

At the end of this chapter and each following chapter, you’ll find a

“Technical Notes” section. These notes provide additional information

about the technology discussed in the chapter and tell you where to get

more information about that technology. Placing these notes at the end

of the chapters helps keep the flow of the main text moving forward

rather than stopping to discuss each detail along the way.

Matching a North American Phone Number

Now we’ll match a North American phone number with a regular expression. Type the

phone number shown here into the lower section of Regexpal:

707-827-7019

Do you recognize it? It’s the number for O’Reilly Media.

Let’s match that number with a regular expression. There are lots of ways to do this,

but to start out, simply enter the number itself in the upper section, exactly as it is

written in the lower section (hold on now, don’t sigh):

707-827-7019

2 | Chapter 1: What Is a Regular Expression?

You can limit the range of digits more precisely and get the same result using a more

specific list of digits to match, such as the following:

[012789]

This will match only those digits listed, that is, 0, 1, 2, 7, 8, and 9. Try it in the upper

box. Once again, every digit in the lower box will be highlighted in alternating colors.

To match any 10-digit, North American phone number, whose parts are separated by

hyphens, you could do the following:

[0-9][0-9][0-9]-[0-9][0-9][0-9]-[0-9][0-9][0-9][0-9]

This will work, but it’s bombastic. There is a better way with something called a

shorthand.

Using a Character Shorthand

Yet another way to match digits, which you saw at the beginning of the chapter, is with

\d which, by itself, will match all Arabic digits, just like [0-9]. Try that in the top section

and, as with the previous regular expressions, the digits below will be highlighted. This

kind of regular expression is called a character shorthand. (It is also called a character

escape, but this term can be a little misleading, so I avoid it. I’ll explain later.)

To match any digit in the phone number, you could also do this:

\d\d\d-\d\d\d-\d\d\d\d

Repeating the \d three and four times in sequence will exactly match three and four

digits in sequence. The hyphen in the above regular expression is entered as a literal

character and will be matched as such.

What about those hyphens? How do you match them? You can use a literal hyphen (-)

as already shown, or you could use an escaped uppercase D (\D), which matches any

character that is not a digit.

This sample uses \D in place of the literal hyphen.

\d\d\d\D\d\d\d\D\d\d\d\d

Once again, the entire phone number, including the hyphens, should be highlighted

this time.

Matching Any Character

You could also match those pesky hyphens with a dot (.):

\d\d\d.\d\d\d.\d\d\d\d

The dot or period essentially acts as a wildcard and will match any character (except,

in certain situations, a line ending). In the example above, the regular expression

matches the hyphen, but it could also match a percent sign (%):

Matching Any Character | 5

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