Pro Perl Debugging.pdf

Pro Perl Debugging

From Professional to Expert

RICHARD FOLEY WITH ANDY LESTER

Pro Perl Debugging: From Professional to Expert

Lead Editor: Jason Gilmore

Technical Reviewer: Andy Lester

Editorial Board: Steve Anglin, Dan Appleman, Ewan Buckingham, Gary Cornell, Tony Davis, Jason Gilmore,

Jonathan Hassell, Chris Mills, Dominic Shakeshaft, Jim Sumser

Associate Publisher: Grace Wong

Project Manager: Emily K. Wolman

Copy Edit Manager: Nicole LeClerc

Copy Editor: Julie Smith

Production Manager: Kari Brooks-Copony

Production Editor: Linda Marousek

Compositor and Artist: Kinetic Publishing Services, LLC

Proofreader: Sue Boshers

Indexer: Rebecca Plunkett

Cover Designer: Kurt Krames

Manufacturing Manager: Tom Debolski

Library of Congress Cataloging-in-Publication Data

Foley, Richard.

Pro Perl debugging : from professional to expert / Richard Foley with

Andy Lester.

p. cm.

Includes bibliographical references and index.

ISBN 1-59059-454-1 (alk. paper)

1. Perl (Computer program language) 2. Debugging in computer science.

I. Lester, Andy. II. Title.

QA76.73.P22F62 2005

005.13

3—dc22

2005016006

electronic or mechanical, including photocopying, recording, or by any information storage or retrieval

system, without the prior written permission of the copyright owner and the publisher.

ISBN: 1-59059-454-1

Printed and bound in the United States of America 9 8 7 6 5 4 3 2 1

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′

I’d like to dedicate this book to my wife, Joy, and to my daughters, Catherine and Jennifer.

Without them it would all seem rather pointless—even if they do call me an angeber

(show-off ) while pointing to daddy’s name as the actual author of a programming book.

And to Spot, for being a friend for 15 years.

—Richard

For Amy and Quinn, the two girls who make me laugh the most.

—Andy

Contents at a Glance

About the Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix

CHAPTER 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

CHAPTER 2

Inspecting Variables and Getting Help . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

CHAPTER 3

Controlling Program Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

CHAPTER 4

Debugging a Simple Command Line Program . . . . . . . . . . . . . . . . . . . 39

CHAPTER 5

Tracing Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

CHAPTER 6

Debugging Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

CHAPTER 7

Debugging Object-Oriented Perl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

CHAPTER 8

Using the Debugger As a Shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

CHAPTER 9

Debugging a CGI Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

CHAPTER 10

Perl Threads and Forked Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

CHAPTER 11

Debugging Regular Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

CHAPTER 12

Debugger Customization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

CHAPTER 13

Optimization and Performance Hints and Tips . . . . . . . . . . . . . . . . . 211

CHAPTER 14

Command Line and GUI Debuggers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231

CHAPTER 15

Comprehensive Command Reference . . . . . . . . . . . . . . . . . . . . . . . . . . 239

CHAPTER 16

Book References and URLs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

Contents

About the Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix

CHAPTER 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

What Is It? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Down the Rabbit Hole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Why Should You Use the Perl Debugger? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Using the Debugger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Book Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Section 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Section 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Section 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Technical Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

CHAPTER 2 Inspecting Variables and Getting Help . . . . . . . . . . . . . . . . . . . . . 7

A Gentle Introduction to the Debugger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Reviewing the Debugger Help Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Going Beyond Help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Supplying a Program Name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

CHAPTER 3 Controlling Program Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

A Sample Program: charcount . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Running charcount . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Debugging a Perl Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Reviewing Executed Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

vii

■

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