Perl For Dummies E-Book

Paul Hoffman

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 535

Veröffentlichungsjahr: 2011

Beschreibung

In the days before personal computers, BASIC was the easy programming language to learn, and serious programmers learned FORTRAN or COBOL to do "real work." Today, many people have discovered that Perl is both a great beginning programming language and one that enables them to write powerful programs with little effort. If you're interested in discovering how to program (or how others program), Perl For Dummies, 4th Edition, is for you. If you already know something about programming (but not about Perl), this book is also for you. If you're already an expert programmer, you're still welcome to read this book; you can just skip the basic stuff (you never know what kind of new tips and tricks you'll pick up). This reference guide shows you how to use Perl under many different operating systems, such as UNIX, many flavors of Windows (Windows 95/98, Windows NT, Windows 2000, Windows Me, and Windows XP), and Macintosh OS 9 and OS X; in fact, Perl runs on many more operating systems than these. Here's a sampling of what Perl For Dummies, 4th Edition, has to offer: * Installing Perl on various platforms * Nailing down the basics of building Perl programs * Working with text and numbers * Constructing lists and working with them * Creating conditionals and loops * Delving into more advanced features such as operators and functions * Reading and writing files and directories * Using subroutines for modularity * Demystifying Web server programs * Creating your own Internet clients The Perl programming language enables you to write fully working computer programs with just a few steps. It's particularly good at common programming tasks, such as reading and writing text files, but it also excels at reducing the work that programmers have to do. Perl For Dummies, 4th Edition, shows you how to do all of that and how to modify programs to your heart's content. After all, one of the common phrases in the world of Perl programmers is, "There's more than one way to do it."

Leseprobe

Perl For Dummies

by Paul Hoffman

Perl For Dummies®, 4th Edition

Published by Wiley Publishing, Inc.909 Third Avenue New York, NY 10022

www.wiley.com

Copyright © 2003 by Wiley Publishing, Inc., Indianapolis, Indiana

Published by Wiley Publishing, Inc., Indianapolis, Indiana

Published simultaneously in Canada

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About the Author

Paul E. Hoffman has written more than a dozen computer books, many of them about the Internet (including Netscape Communicator For Dummies and The Internet, the official book of the Public Television presentation “The Internet Show,” both published by Wiley Publishing, Inc.). In fact, he’s been active on the Internet for more than 20 years. He is the founder of the VPN Consortium, and has written many of the programs used on that group’s Web site. He lives in Santa Cruz, California.

Author’s Acknowledgments

The Perl world is full of very helpful people who answer questions for just about anyone. Perl’s main developer, Larry Wall, started this trend when he released Perl, and now hundreds of people exist on various mailing lists and Web sites who keep the spirit of cooperation alive. Many of my ideas in this book have come from things that these people have said in different forums over the past many years. Tens of thousands of hours have been spent on making Perl free and useful, and I’m grateful for all this effort by Perl enthusiasts all over the world (and you should be, too!). It is my hope that readers of this book will become enamored not only with Perl, but with creating Perl software that will be freely available.

This is my fourth edition of Perl For Dummies, and I’d like to repeat what I said in my very first book. Writing for computer novices is always easier if you have a few of them around asking you questions. My circle of novices and ex-novices keeps me on my toes and reminds me what is not obvious, how frustrating it can be when the system is designed by know-it-all dweebs, and what parts are fun. I am indebted to my friends, my family, and my family-by-choice.

Special thanks to Kala Schrager, the project editor, who spent long hours improving this edition of the book, and for this I am very grateful. Many other folks at Wiley Publishing (and you can find out who they are on the next page) also helped to bring this book to your hands, and I am thankful for their effort and patience.

Publisher’s Acknowledgments

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Some of the people who helped bring this book to market include the following:

Acquisitions, Editorial, and Media Development

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Contents

Title

Introduction

Who You Are

What You Need to Know First

What You’ll Find in This Book

A Word about Program Examples

Icons Used in This Book

Part I : Getting Started with Perl

Chapter 1: Perl’s Place in the Programming World

Understanding the Purpose of Programming

Making Computers Compute

Translating Your Language into Computer Language

Designing Computer Languages

Appreciating the Benefits of Perl

Many Versions, One Perl

Differentiating Between Perl 5 and Perl 5.6

Exploring the New Features of Perl 5.8

Chapter 2: Running Perl on Your Computer

Perl Isn’t Just for UNIX Anymore

UNIX: Perl’s First Home

ActivePerl on Windows

Perl for Mac Users

Working with Perl on the Command Line

Other Perls

Utilizing the Comprehensive Perl Archive Network

Working with the ActivePerl Package Manager

Getting Help

Chapter 3: Diving into the Guts of Perl

Grabbing a Text Editor

Examining Some Basic Components of a Perl Program

Creating Perl Programs Using Statements

Keeping Tabs on Statements: Indenting and Spacing

A Five-Minute Guide to Numbers and Text

Working with Variables and Literals

Chapter 4: A Perl Program Tour, Times Two

Examining the Inside of a Sample Program

Exploring a Program with More Features

Avoiding the Most Common Oversights

Part II : The Basic Perl Programming Ingredients

Chapter 5: Terrific Text

Checking Your Work: The print Statement

Defining Strings

Differentiating between Visible Characters and Character Values

Quoting Text

Manipulating Strings

Performing Simple String Transformations

Getting Information from Strings

Writing for the World in Perl 5.6 and Perl 5.8

Chapter 6: Nifty Numbers

Contrasting Integers and Real Numbers

Using Perl’s Basic Math Operators

Doing Math and an Assignment at the Same Time

Autoincrementing and Autodecrementing

Employing Simple Numeric Functions

Converting Numbers into Strings

Working with Really Big Numbers

Counting in Nondecimal Number Systems

Chapter 7: Learning to Love Lists and Hashes

Listing the Basics

Specifying Elements and Slices of Lists

Using Lists to Simplify Basic Tasks

Using the print Statement with Lists

Adding and Removing List Elements

Splitting Strings with the split Function

Using Scalar Variables

Employing Existing Lists

Distinguishing Context Types

Using List::Util in Perl 5.8

Understanding the Basics of Working with Hashes

Writing Hash Data to a File

Creating Multidimensional Lists

Creating Hashes Consisting of Lists

Writing the Files for Lists within Lists

Chapter 8: Creating Cool Conditionals and Lovely Loops

Exploring Basic Logic Statements

Working with Conditional Statements

Going Around in Loops

Creating switch structures in Perl 5.8

Using Expressions as Logical Values

Caveat Emptor: Jumping around Programs by Using Labels

Chapter 9: Doing Advanced Stuff with Operators and Functions

Using Undefined Variables

Looking for Strings within Strings

Applying Some Fancy Formatting to Text and Numbers

Tracking Time

Picking Random Numbers

Shifting Bits with Bit-Level Operators

Converting Lists to Strings

Rearranging Lists

Part III : The Nuts and Bolts of Perl

Chapter 10: The Files Go In, The Files Go Out

Understanding Perl File Types

Opening and Closing Files

Specifying Filenames and DirectoryPaths for Various Operating Systems

Reading from a Text File the Easy Way

Writing Text to a File the Easy Way

Running Tests to Get Information on a File

Moving File Streams in UNIX: Standard In, Standard Out, and Standard Error

Chapter 11: Beyond File and Directory Basics

Reading from and Writing to Binary Files

Changing File Characteristics

Grouping Filenames by Matching Characters

File Features Strictly for UNIX Users

Getting the Nitty-Gritty Stats on Files

Working with Directories of Files

Chapter 12: Stringing Along: Pattern Matching and Regular Expressions

Working with Regular Expressions

Making Inexact Matches in Regular Expressions

Searching the Beginning or End of a String

Using Quantifiers for Numerical Matches

Getting the Match Results

More Programming Magic with the m// Operator

Using the grep Function

Doing Simple Substitutions with the s/// Operator

Using the split Function with More-Advanced Regular Expressions

Using the tr/// Operator

Chapter 13: Looking Like a Pro: Subroutines, Imported Code, and Graceful Exits

Saving Steps with Subroutines

Importing Prewritten Perl Code into Your Programs

Ending Perl Programs Gracefully

Part IV : Advanced Perl Demystified

Chapter 14: Perl and CGI: Web Server Programs Demystified

Writing CGI Programs in Perl

Using Environment Variables

Gathering Information from HTML Forms

Using GET and POST to Collect Form Data

Displaying Output to the User

Creating an HTML Form

Using Redirection to Link to Other Sites

Exploring a Few Other Environment Variables

Working with Apache and Perl

Handling CGI and HTML with Mason

Chapter 15: Perl Gets Cozy with the Web, E-Mail, and the Rest of the Internet

Using the libwww-perl Library

Getting Your E-Mail

Pinging with Perl

Using Net::FTP to Grab Files

Delving into Domain Names with Perl

Chapter 16: Using Perl as a Gateway to XML and Web Services

Exploring the Role of Perl and XML in Web Programming

Combining XML and Perl

Checking a Document for Accuracy

How Do You Want to Read It?

Writing an XML Document

Reading and Writing XML in Other Ways

Looking into Web Services

Connecting Web Services and Perl

Chapter 17: Dancing with Databases

Managing Databases Using Hashes

Opening Databases

Closing Databases

Tips on Opening and Closing Databases

Chapter 18: Controlling Your Computer from Perl

Getting with the System

Controlling a Windows or Mac Computer with Perl

Using UNIX-Only System Functions

Chapter 19: Object-Oriented Perl

Understanding the Advantages Object-Oriented Programming

Defining Objects, Methods, and Arguments

Perl’s Objects Made Easy

Considering a Real-World Object Example

Part V : The Part of Tens

Chapter 20: Ten Guidelines for Programming with Style

Examining the Perl Creator’s Style Preferences

Choosing Your Operator

Parentheses Are Your Friends

Flexible Ordering for Conditionals

Commenting about Comments

Standout Line Treatments

Comments Cohabitating with Code

Naming Your Variables Descriptively

Capital Offense, or Not?

The Beauty of Blank Lines

Chapter 21: Ten Really Short, Really Useful Perl Programs

Collecting Unique Lines

Getting Rid of Multiple Blank Lines

Printing Lines from a File in Sorted Order

Printing a Range of Lines from a File

Listing Just the Files in a Directory

Listing a Directory by Size

Sorting Directories by Extension

Creating a Simple Calculator

Randomizing a List

Generating Random Mnemonic Passwords

Part VI : Appendix

Appendix: The Great Perl Reference

Perl Operators

Perl’s Operator Hierarchy

Perl’s Functions and Statements

Perl’s Special Variables

Perl’s Predefined File Handles

Introduction

A ssuming that you want to venture into programming, your first step is to pick a specific programming language to start out with. Because you’re reading this book, I’m guessing that you’re seriously thinking about programming with Perl. I applaud your choice. Like human languages, some programming languages are easier to learn than others. Perl is one of the easiest programming languages to work with, yet it’s as powerful as many languages that are much more difficult to master.

The Perl programming language allows you to create fully working computer programs with just a few steps. It’s particularly good at common programming tasks, such as reading and writing text files, but it also excels at reducing the work that programmers have to do — more so than other popular languages, such as C and Java.

Who You Are

Your reasons for wanting to learn a programming language probably boil down to the following:

A fascination with how computers work

A desire to create your own programs to control your computer

For professional development (for example, you want to advance to programmer status)

You may also want to get acquainted with a programming language because you work with programmers and you wonder what it is that they do all day. Understanding programming definitely helps you to appreciate what it takes to be a good programmer, even if you don’t become one yourself.

If you’re interested in discovering how to program (or how others program), Perl For Dummies, 4th Edition is for you. If you already know something about programming (but not about Perl), this book is also for you. If you’re already an expert programmer, you’re still welcome to read this book; you can just skip the basic stuff (you never know what kind of new tips and tricks you’ll pick up).

After finding out how to program with Perl, you may decide to go on and become someone who makes a living as a Perl programmer. Or, you may decide that, although programming is interesting, it isn’t something that you want to do full time. And, a chance exists (although a slight one) that after you learn how to program in Perl, you may discover that you like programming, but you dislike Perl.

Fortunately, you can also apply most of the Perl programming skills that you can pick up from this book to another programming language later on. Perl is simpler to work with than most other programming languages — and Perl uses many of the same concepts as other languages do, which makes it an excellent introductory language.

What You Need to Know First

This book covers how to use Perl under many different operating systems, such as UNIX, many flavors of Windows (Windows 9 5/98, Windows NT, Windows 2000, Windows Me, and Windows XP), and Macintosh OS 9 and OS X; in fact, Perl runs on many more operating systems than these. To use this book to learn Perl programming, you need to know at least one of these operating systems. You don’t need to know more than one operating system, and very few folks out there know how to use all four. If you’re one of those people who’s familiar with all four operating systems, you can enjoy the title of Total Computer Dweeb and be comfortable in the fact that few others in the world share your unique skills.

In short, you don’t need to know anything about programming up front, or even what Perl is, to get lots of value from this book. However, you do need to know the basics of using your computer system so that you can load Perl and create text files that Perl can use as programs.

What You’ll Find in This Book

Because Perl For Dummies, 4th Editionis meant for both programming novices and folks who already know something about programming, I arranged the book so that both groups of people can find what they want quickly. You may want to read this book straight through from beginning to end, or you may be one of those folks who enjoys skipping to just what you need. In either case, you need to know how this book is organized.

Part I: Getting Started with Perl

Part I tells you what programming is all about, what Perl is, what makes it different from other programming languages, and what it means “to program.” This part contains some example programs so that you can see what they look like and how they are put together. You also get some help in installing Perl and running Perl on various operating systems.

Part II: The Basic Perl Programming Ingredients

In Part II, I cover the basic elements of programming with Perl — including techniques for working with text and numbers, plus in-the-trenches programming stuff like lists, strings, operators, loops, and conditional statements. When you’re done perusing this part, you can probably write a few short programs of your own.

Part III: The Nuts and Bolts of Perl

This part of the book shows you how to structure a complete Perl program, put together larger and more complex programs, tell Perl to read and write files on your computer, and write programs that know how to talk to a Web server.

Part IV: Advanced Perl Demystified

After you’re comfortable with Perl and feeling adventurous, you can dip into this part of the book, which covers a number of advanced Perl topics. Novice programmers aren’t expected to use these features immediately, but if you zoom ahead to these chapters (maybe you’re saying, “Nah, that’s not me,” but you may surprise yourself later), you’ll find lots of useful information to rev up your Perl programs.

Part V: The Part of Tens

This part of the book contains some nice, quick lists of interesting information about Perl. If you like round numbers, you’ll be happy to know that they’re all organized in groups of ten.

Part VI: Appendix

Part VI, as you may have guessed, contains the appendix. I list some handy Perl references, such as operators, special variables, and predefined file handles.

A Word about Program Examples

Throughout the book, you can find examples of Perl code that look like the following line:

print “Hello, world!\n”;

You will also see examples of this same kind of typestyle in the body text like this to indicate that this text is a part of a Perl program. You can also find multiple lines of code neatly enclosed in gray boxes. The single lines of code are usually Perl statements (or portions of a statement) and the multiple lines are generally Perl programs. (Yes, you can write an entire program in Perl with just three or four lines.) Not to worry, though. This books tells you all about the difference between statements and programs (and functions and strings and other programming conventions) that are displayed in code font.

Icons Used in This Book

One of the fun things about writing a For Dummies book is that you get to use these clever icons to point out items of special interest.

Hopefully, you’ll find everything in the book really useful, but these items are especially noteworthy.

This icon alerts you to something that you should definitely watch out for. A couple of important “gotchas” are buried in Perl, and these warnings can help steer you clear of them.

This icon appears next to anything you need to remember later on when you’re doing other kinds of stuff with Perl.

Stop here for a side note about something especially high-end. This icon points out technical information that isn’t critical to know, but handy nonetheless.

Part I

Getting Started with Perl

In this part. . .

You’ve got to start somewhere, and the beginning is the best place, is it not? In these first few chapters, you find out what a programming language is, what Perl is, how to get Perl up and running on your particular operating system, and what a couple of substantial Perl programs look like.

Chapter 1

Perl’s Place in the Programming World

In This Chapter

Understanding programming languages

Comparing Perl to other languages

Using Perl with emerging technologies

M any people want to know exactly what makes their computer programs tick. They have a nagging itch to find out what’s “under the hood” of their computers, beyond the chips and wires. They want to find out how they can create new and better programs and how it is that programmers can make so much money yet look like they dress in the dark.

Don’t assume that everyone who programs or writes books about programming is a young whippersnapper. Without getting too specific, let’s just say that my college days are way, way behind me. When I worked with computers back then, I often used punched cards and paper tape — ah, those wonderful pre-PC days.

In pre-PC days, BASIC was the easy language to learn, and serious programmers learned FORTRAN or COBOL to do “real work.” But many people discovered that you could accomplish a lot with plain old BASIC. Today, many people have discovered that Perl is a great beginning programming language because it’s simple to use and yet you can create powerful programs with little effort. Sure, you can immerse yourself in more difficult languages, such as C++ or Java, but you can probably learn Perl faster and find yourself doing what you want to do just as well, if not better.

Understanding the Purpose of Programming

If you’re new to the concept of programming, you may be asking yourself, “Why am I learning how to program?” Sure, programs control computers, but that doesn’t mean that everyone should become a programmer.

When personal computers appeared on the scene about 25 years ago, almost no commercial software existed, and the software that did exist was pretty primitive. If you wanted to do anything special, you had to learn to program so that you could create programs to meet your specific needs. By 1981, when the IBM PC came out, plenty of commercial programs were available and users no longer needed to program their computers — the software did it for them.