精通Perl编程

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"《Mastering Perl》是Brian Doy的一本深入学习Perl编程语言的书籍，它是《Learning Perl》的进阶版本，旨在帮助已经掌握基础Perl知识的读者提升技能和理解深度。这本书由O'Reilly Media, Inc.于2007年出版，涵盖了Perl的高级主题和实践应用。" 在《Mastering Perl》中，作者Brian Doy深入探讨了Perl编程的各种核心概念和技术，包括但不限于： 1. **正则表达式**：书中详细介绍了Perl中的正则表达式，包括复杂的模式匹配、捕获组、后向引用、零宽度断言等，这些都是Perl处理文本和数据的强大工具。 2. **高级数据结构**：除了基础的数据结构如数组和哈希，还讲解了复杂的数据结构，如自定义对象、多重数组、关联数组、链表和树形结构，以及如何高效地操作它们。 3. **文件和I/O**：涵盖了文件处理的各个方面，如文件打开、读写、文件指针、模式匹配和文件测试操作符，以及高级I/O技术，如管道、套接字和并发I/O。 4. **模块和CPAN**：介绍了Perl的模块系统，如何使用CPAN（Comprehensive Perl Archive Network）来查找和安装第三方模块，以及如何编写和发布自己的模块。 5. **错误处理和调试**：讨论了Perl的异常处理机制，如die和warn，以及如何有效地调试Perl程序，包括使用DBI调试器和其他工具。 6. **函数和过程**：深入讲解了Perl的函数特性，包括匿名函数、闭包、引用和回调，以及如何设计和优化函数接口。 7. **面向对象编程**：介绍了Perl的面向对象编程，包括类、继承、多态和模块化设计，以及如何利用 Moose 框架进行更现代的面向对象编程。 8. **高级脚本和程序设计**：涵盖了模块化程序设计、配置管理、命令行参数处理、性能优化和脚本调试技巧。 9. **国际化和本地化**：讲述了如何在Perl程序中实现国际化（i18n）和本地化（l10n），包括日期、时间、货币和文本的处理。 10. **Perl最佳实践**：作者分享了他的经验，提供了关于代码风格、命名约定、文档编写和代码维护的最佳实践。本书适合已经对Perl有一定基础的开发者阅读，通过学习，读者将能够更熟练地运用Perl解决实际问题，编写出更高效、可维护的代码。此外，书中的案例和练习题有助于读者巩固知识，提高实际编程能力。

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

I can use this program from the command line to search for patterns in files. Here I

search for the pattern new in all of the Perl programs in the current directory:

% perl-grep.pl new *.pl

Regex is [new]

my $regexp = Regexp::English->new

my $graph = GraphViz::Regex->new($regex);

[ qr/\G(\n)/, "newline" ],

{ ( $1, "newline char" ) }

print YAPE::Regex::Explain->new( $ARGV[0] )->explain;

What happens if I give it an invalid regex? I try it with a pattern that has an opening

parenthesis without its closing mate:

$ ./perl-grep.pl "(perl" *.pl

Regex is [(perl]

Unmatched ( in regex; marked by <-- HERE in m/( <-- HERE perl/

at ./perl-grep.pl line 10, <> line 1.

When I interpolate the regex in the match operator, Perl compiles the regex and im-

mediately complains, stopping my program. To catch that, I want to compile the regex

before I try to use it.

The

qr// is a regex quoting operator that stores my regex in a scalar (and as a quoting

operator, its documentation shows up in perlop). The qr// compiles the pattern so it’s

ready to use when I interpolate $regex in the match operator. I wrap the eval operator

around the qr// to catch the error, even though I end up die-ing anyway:

#!/usr/bin/perl

# perl-grep2.pl

my $pattern = shift @ARGV;

my $regex = eval { qr/$pattern/ };

die "Check your pattern! $@" if $@;

while( <> )

{

print if m/$regex/;

}

The regex in $regex has all of the features of the match operator, including back refer-

ences and memory variables. This pattern searches for a three-character sequence where

the first and third characters are the same, and none of them are whitespace. The input

is the plain text version of the perl documentation page, which I get with

perldoc -t:

% perldoc -t perl | perl-grep2.pl "\b(\S)\S\1\b"

perl583delta Perl changes in version 5.8.3

perl582delta Perl changes in version 5.8.2

perl581delta Perl changes in version 5.8.1

perl58delta Perl changes in version 5.8.0

perl573delta Perl changes in version 5.7.3

perl572delta Perl changes in version 5.7.2

perl571delta Perl changes in version 5.7.1

perl570delta Perl changes in version 5.7.0

8 | Chapter 2: Advanced Regular Expressions

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