Intermediate Perl Table of Contents Intermediate Perl Foreword Preface Structure of This Book Conventions Used in This Book Using Code Examples

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2 Intermediate Perl Table of Contents Intermediate Perl Foreword Preface Structure of This Book Conventions Used in This Book Using Code Examples Comments and Questions Safari Enabled Acknowledgments Chapter 1. Introduction Section 1.1. What Should You Know Already? Section 1.2. What About All Those Footnotes? Section 1.3. What's with the Exercises? Section 1.4. What If I'm a Perl Course Instructor? Chapter 2. Intermediate Foundations Section 2.1. List Operators Section 2.2. Trapping Errors with eval Section 2.3. Dynamic Code with eval Section 2.4. Exercises Chapter 3. Using Modules Section 3.1. The Standard Distribution Section 3.2. Using Modules Section 3.3. Functional Interfaces Section 3.4. Selecting What to Import Section 3.5. Object-Oriented Interfaces Section 3.6. A More Typical Object-Oriented Module: Math::BigInt Section 3.7. The Comprehensive Perl Archive Network 2

3 Section 3.8. Installing Modules from CPAN Section 3.9. Setting the Path at the Right Time Section Exercises Chapter 4. Introduction to References Section 4.1. Performing the Same Task on Many Arrays Section 4.2. Taking a Reference to an Array Section 4.3. Dereferencing the Array Reference Section 4.4. Getting Our Braces Off Section 4.5. Modifying the Array Section 4.6. Nested Data Structures Section 4.7. Simplifying Nested Element References with Arrows Section 4.8. References to Hashes Section 4.9. Exercises Chapter 5. References and Scoping Section 5.1. More Than One Reference to Data Section 5.2. What If That Was the Name? Section 5.3. Reference Counting and Nested Data Structures Section 5.4. When Reference Counting Goes Bad Section 5.5. Creating an Anonymous Array Directly Section 5.6. Creating an Anonymous Hash Section 5.7. Autovivification Section 5.8. Autovivification and Hashes Section 5.9. Exercises Chapter 6. Manipulating Complex Data Structures Section 6.1. Using the Debugger to View Complex Data Section 6.2. Viewing Complex Data with Data::Dumper Section 6.3. YAML Section 6.4. Storing Complex Data with Storable Section 6.5. Using the map and grep Operators 3

4 Section 6.6. Applying a Bit of Indirection Section 6.7. Selecting and Altering Complex Data Section 6.8. Exercises Chapter 7. Subroutine References Section 7.1. Referencing a Named Subroutine Section 7.2. Anonymous Subroutines Section 7.3. Callbacks Section 7.4. Closures Section 7.5. Returning a Subroutine from a Subroutine Section 7.6. Closure Variables as Inputs Section 7.7. Closure Variables as Static Local Variables Section 7.8. Exercise Chapter 8. Filehandle References Section 8.1. The Old Way Section 8.2. The Improved Way Section 8.3. The Even Better Way Section 8.4. IO::Handle Section 8.5. Directory Handle References Section 8.6. Exercises Chapter 9. Practical Reference Tricks Section 9.1. Review of Sorting Section 9.2. Sorting with Indices Section 9.3. Sorting Efficiently Section 9.4. The Schwartzian Transform Section 9.5. Multi-Level Sort with the Schwartzian Transform Section 9.6. Recursively Defined Data Section 9.7. Building Recursively Defined Data Section 9.8. Displaying Recursively Defined Data Section 9.9. Exercises Chapter 10. Building Larger Programs 4

5 Section The Cure for the Common Code Section Inserting Code with eval Section Using do Section Using require Section require Section The Problem of Namespace Collisions Section Packages as Namespace Separators Section Scope of a Package Directive Section Packages and Lexicals Section Exercises Chapter 11. Introduction to Objects Section If We Could Talk to the Animals... Section Introducing the Method Invocation Arrow Section The Extra Parameter of Method Invocation Section Calling a Second Method to Simplify Things Section A Few Notes Section Overriding the Methods Section Starting the Search from a Different Place Section The SUPER Way of Doing Things Section What to Do Section Where We Are So Far... Section Exercises Chapter 12. Objects with Data Section A Horse Is a Horse, of Course of Courseor Is It? Section Invoking an Instance Method Section Accessing the Instance Data Section How to Build a Horse Section Inheriting the Constructor Section Making a Method Work with Either Classes or Instances 5

6 Section Adding Parameters to a Method Section More Interesting Instances Section A Horse of a Different Color Section Getting Our Deposit Back Section Don't Look Inside the Box Section Faster Getters and Setters Section Getters That Double as Setters Section Restricting a Method to Class-Only or Instance-Only Section Exercise Chapter 13. Object Destruction Section Cleaning Up After Yourself Section Nested Object Destruction Section Beating a Dead Horse Section Indirect Object Notation Section Additional Instance Variables in Subclasses Section Using Class Variables Section Weakening the Argument Section Exercise Chapter 14. Some Advanced Object Topics Section UNIVERSAL Methods Section Testing Our Objects for Good Behavior Section AUTOLOAD as a Last Resort Section Using AUTOLOAD for Accessors Section Creating Getters and Setters More Easily Section Multiple Inheritance Section Exercises Chapter 15. Exporter Section What use Is Doing Section Importing with Exporter Section 6

7 Section %EXPORT_TAGS Section Exporting in a Primarily OO Module Section Custom Import Routines Section Exercises Chapter 16. Writing a Distribution Section There's More Than One Way To Do It Section Using h2xs Section Embedded Documentation Section Controlling the Distribution with Makefile.PL Section Alternate Installation Locations (PREFIX=...) Section Trivial make test Section Trivial make install Section Trivial make dist Section Using the Alternate Library Location Section Exercise Chapter 17. Essential Testing Section More Tests Mean Better Code Section A Simple Test Script Section The Art of Testing Section The Test Harness Section Writing Tests with Test::More Section Testing Object-Oriented Features Section A Testing To-Do List Section Skipping Tests Section More Complex Tests (Multiple Test Scripts) Section Exercise Chapter 18. Advanced Testing Section Testing Large Strings Section Testing Files Section Testing STDOUT or STDERR Section Using Mock Objects 7

8 Section Testing POD Section Coverage Testing Section Writing Your Own Test::* Modules Section Exercises Chapter 19. Contributing to CPAN Section The Comprehensive Perl Archive Network Section Getting Prepared Section Preparing Your Distribution Section Uploading Your Distribution Section Announcing the Module Section Testing on Multiple Platforms Section Consider Writing an Article or Giving a Talk Section Exercise Appendix A. Answers to Exercises Section A.1. Answers for Chapter 2 Section A.2. Answers for Chapter 3 Section A.3. Answers for Chapter 4 Section A.4. Answers for Chapter 5 Section A.5. Answers for Chapter 6 Section A.6. Answer for Chapter 7 Section A.7. Answers for Chapter 8 Section A.8. Answers for Chapter 9 Section A.9. Answers for Chapter 10 Section A.10. Answers for Chapter 11 Section A.11. Answer for Chapter 12 Section A.12. Answer for Chapter 13 Section A.13. Answers for Chapter 14 Section A.14. Answers for Chapter 15 Section A.15. Answer for Chapter 16 Section A.16. Answer for Chapter 17 Section A.17. Answers for Chapter 18 8

9 Section A.18. Answer for Chapter 19 About the Author Colophon Index SYMBOL A B C D E F G H I K L M N O P R S T U V W X Y 9

10 Intermediate Perl By brian d foy, Tom Phoenix, Randal L. Schwartz... Publisher: O'Reilly Pub Date: March 2006 Print ISBN-10: Print ISBN-13: Pages: 278 Table of Contents Index Perl is a versatile, powerful programming language used in a variety of disciplines, ranging from system administration to web programming to database manipulation. One slogan of Perl is that it makes easy things easy and hard things possible. Intermediate Perl is about making the leap from the easy things to the hard ones. Originally released in 2003 as Learning Perl Objects, References, and Modules and revised and updated for Perl 5.8, this book offers a gentle but thorough introduction to intermediate programming in Perl. Written by the authors of the best-selling Learning Perl, it picks up where that book left off. Topics include: Packages and namespaces References and scoping Manipulating complex data structures Object-oriented programming Writing and using modules Testing Perl code Contributing to CPAN Following the successful format of Learning Perl, we designed each chapter in the book to be small enough to be read in just an hour or two, ending with a series of exercises to help you practice what you've learned. To use the book, you just need to be familiar with the material in Learning Perl and have ambition to go further. Perl is a different language to different people. It is a quick scripting tool for some, 10

11 and a fully-featured object-oriented language for others. It is used for everything from performing quick global replacements on text files, to crunching huge, complex sets of scientific data that take weeks to process. Perl is what you make of it. But regardless of what you use Perl for, this book helps you do it more effectively, efficiently, and elegantly. Intermediate Perl is about learning to use Perl as a programming language, and not just a scripting language. This is the book that turns the Perl dabbler into the Perl programmer. 11

12 Intermediate Perl By brian d foy, Tom Phoenix, Randal L. Schwartz... Publisher: O'Reilly Pub Date: March 2006 Print ISBN-10: Print ISBN-13: Pages: 278 Table of Contents Index Intermediate Perl Foreword Preface Structure of This Book Conventions Used in This Book Using Code Examples Comments and Questions Safari Enabled Acknowledgments Chapter 1. Introduction Section 1.1. What Should You Know Already? Section 1.2. What About All Those Footnotes? Section 1.3. What's with the Exercises? Section 1.4. What If I'm a Perl Course Instructor? Chapter 2. Intermediate Foundations Section 2.1. List Operators Section 2.2. Trapping Errors with eval Section 2.3. Dynamic Code with eval Section 2.4. Exercises Chapter 3. Using Modules Section 3.1. The Standard Distribution Section 3.2. Using Modules Section 3.3. Functional Interfaces 12

13 Section 3.4. Selecting What to Import Section 3.5. Object-Oriented Interfaces Section 3.6. A More Typical Object-Oriented Module: Math::BigInt Section 3.7. The Comprehensive Perl Archive Network Section 3.8. Installing Modules from CPAN Section 3.9. Setting the Path at the Right Time Section Exercises Chapter 4. Introduction to References Section 4.1. Performing the Same Task on Many Arrays Section 4.2. Taking a Reference to an Array Section 4.3. Dereferencing the Array Reference Section 4.4. Getting Our Braces Off Section 4.5. Modifying the Array Section 4.6. Nested Data Structures Section 4.7. Simplifying Nested Element References with Arrows Section 4.8. References to Hashes Section 4.9. Exercises Chapter 5. References and Scoping Section 5.1. More Than One Reference to Data Section 5.2. What If That Was the Name? Section 5.3. Reference Counting and Nested Data Structures Section 5.4. When Reference Counting Goes Bad Section 5.5. Creating an Anonymous Array Directly Section 5.6. Creating an Anonymous Hash Section 5.7. Autovivification Section 5.8. Autovivification and Hashes Section 5.9. Exercises Chapter 6. Manipulating Complex Data Structures Section 6.1. Using the Debugger to View Complex Data Section 6.2. Viewing Complex Data with Data::Dumper Section 6.3. YAML Section 6.4. Storing Complex Data with Storable Section 6.5. Using the map and grep Operators Section 6.6. Applying a Bit of Indirection 13

14 Section 6.7. Selecting and Altering Complex Data Section 6.8. Exercises Chapter 7. Subroutine References Section 7.1. Referencing a Named Subroutine Section 7.2. Anonymous Subroutines Section 7.3. Callbacks Section 7.4. Closures Section 7.5. Returning a Subroutine from a Subroutine Section 7.6. Closure Variables as Inputs Section 7.7. Closure Variables as Static Local Variables Section 7.8. Exercise Chapter 8. Filehandle References Section 8.1. The Old Way Section 8.2. The Improved Way Section 8.3. The Even Better Way Section 8.4. IO::Handle Section 8.5. Directory Handle References Section 8.6. Exercises Chapter 9. Practical Reference Tricks Section 9.1. Review of Sorting Section 9.2. Sorting with Indices Section 9.3. Sorting Efficiently Section 9.4. The Schwartzian Transform Section 9.5. Multi-Level Sort with the Schwartzian Transform Section 9.6. Recursively Defined Data Section 9.7. Building Recursively Defined Data Section 9.8. Displaying Recursively Defined Data Section 9.9. Exercises Chapter 10. Building Larger Programs Section The Cure for the Common Code Section Inserting Code with eval Section Using do Section Using require Section require 14

15 Section The Problem of Namespace Collisions Section Packages as Namespace Separators Section Scope of a Package Directive Section Packages and Lexicals Section Exercises Chapter 11. Introduction to Objects Section If We Could Talk to the Animals... Section Introducing the Method Invocation Arrow Section The Extra Parameter of Method Invocation Section Calling a Second Method to Simplify Things Section A Few Notes Section Overriding the Methods Section Starting the Search from a Different Place Section The SUPER Way of Doing Things Section What to Do Section Where We Are So Far... Section Exercises Chapter 12. Objects with Data Section A Horse Is a Horse, of Course of Courseor Is It? Section Invoking an Instance Method Section Accessing the Instance Data Section How to Build a Horse Section Inheriting the Constructor Section Making a Method Work with Either Classes or Instances Section Adding Parameters to a Method Section More Interesting Instances Section A Horse of a Different Color Section Getting Our Deposit Back Section Don't Look Inside the Box Section Faster Getters and Setters Section Getters That Double as Setters Section Restricting a Method to Class-Only or Instance-Only Section Exercise 15

16 Chapter 13. Object Destruction Section Cleaning Up After Yourself Section Nested Object Destruction Section Beating a Dead Horse Section Indirect Object Notation Section Additional Instance Variables in Subclasses Section Using Class Variables Section Weakening the Argument Section Exercise Chapter 14. Some Advanced Object Topics Section UNIVERSAL Methods Section Testing Our Objects for Good Behavior Section AUTOLOAD as a Last Resort Section Using AUTOLOAD for Accessors Section Creating Getters and Setters More Easily Section Multiple Inheritance Section Exercises Chapter 15. Exporter Section What use Is Doing Section Importing with Exporter Section Section %EXPORT_TAGS Section Exporting in a Primarily OO Module Section Custom Import Routines Section Exercises Chapter 16. Writing a Distribution Section There's More Than One Way To Do It Section Using h2xs Section Embedded Documentation Section Controlling the Distribution with Makefile.PL Section Alternate Installation Locations (PREFIX=...) Section Trivial make test Section Trivial make install Section Trivial make dist 16

17 Section Using the Alternate Library Location Section Exercise Chapter 17. Essential Testing Section More Tests Mean Better Code Section A Simple Test Script Section The Art of Testing Section The Test Harness Section Writing Tests with Test::More Section Testing Object-Oriented Features Section A Testing To-Do List Section Skipping Tests Section More Complex Tests (Multiple Test Scripts) Section Exercise Chapter 18. Advanced Testing Section Testing Large Strings Section Testing Files Section Testing STDOUT or STDERR Section Using Mock Objects Section Testing POD Section Coverage Testing Section Writing Your Own Test::* Modules Section Exercises Chapter 19. Contributing to CPAN Section The Comprehensive Perl Archive Network Section Getting Prepared Section Preparing Your Distribution Section Uploading Your Distribution Section Announcing the Module Section Testing on Multiple Platforms Section Consider Writing an Article or Giving a Talk Section Exercise Appendix A. Answers to Exercises Section A.1. Answers for Chapter 2 Section A.2. Answers for Chapter 3 17

18 Section A.3. Answers for Chapter 4 Section A.4. Answers for Chapter 5 Section A.5. Answers for Chapter 6 Section A.6. Answer for Chapter 7 Section A.7. Answers for Chapter 8 Section A.8. Answers for Chapter 9 Section A.9. Answers for Chapter 10 Section A.10. Answers for Chapter 11 Section A.11. Answer for Chapter 12 Section A.12. Answer for Chapter 13 Section A.13. Answers for Chapter 14 Section A.14. Answers for Chapter 15 Section A.15. Answer for Chapter 16 Section A.16. Answer for Chapter 17 Section A.17. Answers for Chapter 18 Section A.18. Answer for Chapter 19 About the Author Colophon Index 18

19 Intermediate Perl by Randal L. Schwartz, brian d foy, and Tom Phoenix Copyright (c) 2006, 2003 O'Reilly Media, Inc. All rights reserved. Printed in the United States of America. Published by O'Reilly Media, Inc., 1005 Gravenstein Highway North, Sebastopol, CA O'Reilly books may be purchased for educational, business, or sales promotional use. Online editions are also available for most titles (safari.oreilly.com). For more information, contact our corporate/institutional sales department: (800) or corporate@oreilly.com. Editors: Allison Randal and Tatiana Apandi Production Editor: Darren Kelly Copyeditor: Proofreader: Indexer: Cover Designer: Interior Designer: Illustrators: Chris Downey Nancy Reinhardt Angela Howard Karen Montgomery David Futato Robert Romano, Jessamyn Read, and Lesley Borash Printing History: June 2003: March 2006: First Edition, published as Learning Perl Objects, References & Modules. Second Edition. 19

20 Nutshell Handbook, the Nutshell Handbook logo, and the O'Reilly logo are registered trademarks of O'Reilly Media, Inc. Intermediate Perl, the image of an alpaca, and related trade dress are trademarks of O'Reilly Media, Inc. Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and O'Reilly Media, Inc. was aware of a trademark claim, the designations have been printed in caps or initial caps. While every precaution has been taken in the preparation of this book, the publisher and authors assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. ISBN: [M] 20