www.it-ebooks.info 800 East 96th St., Indianapolis, Indiana, 46240 USA Teach Yourself in 24 Hours Rafe Colburn CGI SECOND EDITION 00 0672324040 FM 8/28/03 9:41 AM Page i www.it-ebooks.info Sams Teach Yourself CGI in 24 Hours, Second Edition Copyright  2003 by Sams Publishing All rights reserved. No part of this book shall be reproduced, stored in a retrieval system, or transmitted by any means, electronic, mechanical, photo- copying, recording, or otherwise, without written permission from the pub- lisher. No patent liability is assumed with respect to the use of the information contained herein. Although every precaution has been taken in the preparation of this book, the publisher and author assume no responsibility for errors or omissions. Nor is any liability assumed for damages resulting from the use of the information contained herein. International Standard Book Number: 0-672-32404-0 Library of Congress Catalog Card Number: 2002107939 Printed in the United States of America First Printing: September 2002 05 04 03 4 3 2 Trademarks All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized. Sams Publishing cannot attest to the accuracy of this information. Use of a term in this book should not be regarded as affecting the validity of any trademark or service mark. Warning and Disclaimer Every effort has been made to make this book as complete and as accurate as possible, but no warranty or fitness is implied. The information provided is on an “as is” basis. The author and the publisher shall have neither liability nor responsibility to any person or entity with respect to any loss or damages aris- ing from the information contained in this book. Bulk Sales Sams Publishing offers excellent discounts on this book when ordered in quan- tity for bulk purchases or special sales. For more information, please contact U.S. Corporate and Government Sales 1-800-382-3419 corpsales@pearsontechgroup.com For sales outside of the U.S., please contact International Sales 1-317-428-3341 international@pearsontechgroup.com ACQUISITIONS EDITOR Betsy Brown DEVELOPMENT EDITOR Scott Meyers MANAGING EDITOR Charlotte Clapp INDEXER Kelly Castell PROOFREADER Suzanne Thomas TECHNICAL EDITORS Greg Perry J. Eric Sloan TEAM COORDINATOR Amy Patton MULTIMEDIA DEVELOPER Dan Scherf INTERIOR DESIGNER Gary Adair COVER DESIGNER Alan Clements PAGE LAYOUT Brad Lenser 00 0672324040 FM 8/28/03 9:41 AM Page ii www.it-ebooks.info Contents at a Glance Introduction 1 Part I An Introduction to CGI 3 Hour 1 Overview of CGI Programming 5 2 Setting Up Your CGI Environment 19 3Downloading, Installing, and Debugging CGI Scripts 35 4Writing Your First CGI Program 53 Part II Capturing User Input 71 Hour 5 Creating HTML Forms 73 6Working with HTTP 91 7Validating User Input 111 8Creating an Email Feedback Form 131 Part III CGI Programming Languages and Tools 147 Hour 9 Web Application Architecture 149 10 Delving Further into Perl 169 11 Other Popular CGI Programming Languages 189 12 Pros and Cons of Alternate Technologies 211 Part IV Building Basic CGI Applications 227 Hour 13 Using Flat Files for Data Storage 229 14 Creating a CGI-Based Message Board 253 15 Session Management 275 16 Building a Simple Shopping Cart 299 17 Content Management with CGI 321 Part V Integrating Databases with CGI 339 Hour 18 Working with Relational Databases 341 19 How to Use the Structured Query Language 355 20 Creating an Online Store 373 00 0672324040 FM 8/26/02 11:04 AM Page iii www.it-ebooks.info Part VI Additional CGI Tips and Tricks 395 Hour 21 Handling Other Content Types 397 22 Securing CGI Scripts 411 23 Creating Custom Error Documents 425 24 Server Side Includes 443 Part VII Appendixes 461 Appendix A MIME Types 463 B Response Codes and Reason Phrases 467 CEnvironment Variables and Request Headers 471 D Summary of Regular Expressions 479 E ASCII Table 483 Index 489 00 0672324040 FM 8/26/02 11:04 AM Page iv www.it-ebooks.info Contents Introduction 1 Part I An Introduction to CGI 3 Hour 1 Overview of CGI Programming 5 Types of Web Applications 6 A History of CGI 6 What Is a CGI Program? 7 How CGI Programs Work 8 How Resources Are Requested 8 Fulfilling the Request 9 Passing Data to a CGI Program 11 Pros and Cons of CGI 11 CGI Programming Languages 13 Perl 13 UNIX Shell 13 The C Language 14 Visual Basic 15 Python 15 Java 16 Summary 16 Q&A 16 Workshop 17 Quiz 17 Quiz Answers 17 2 Setting Up Your CGI Environment 19 The Web Server Itself 19 Hosting Your CGI Scripts 20 Running Your Own Web Server 20 Web Hosting 21 Web-Server Operating Systems 22 UNIX 22 Windows 23 The CGI Environment 23 Web Servers 24 Web-Server Directory Structure 24 How Scripts Are Executed 25 Setting Up Your CGI Development Environment 26 Step 1: Download a Web Server 26 Step 2: Install the Web Server 27 00 0672324040 FM 8/26/02 11:04 AM Page v www.it-ebooks.info Step 3: Download a Perl Interpreter 28 Step 4: Install the Perl Interpreter 28 Step 5: Get the Web Server Up and Running 29 Step 6: Test the Web Server 29 Step 7: Test a Perl CGI Script 30 What If Something Went Wrong? 32 Summary 33 Q&A 33 Workshop 34 Quiz 34 Exercises 34 Quiz Answers 34 3 Downloading, Installing, and Debugging CGI Scripts 35 Downloading Scripts from the Internet 36 Finding the Scripts You Need 36 What to Look for in Publicly-Available Scripts 37 Installing a Downloaded Script 38 Example: Downloading and Installing a Guestbook Script 38 Configuring the Script 39 Installing the Files and Setting Permissions 40 Testing the Script 41 Customizing the Look and Feel 41 Debugging CGI Scripts 42 Finding the Source of an Error 42 Fixing Setup Errors 44 Tools and Techniques for Debugging Your Program Code 47 Compiled Versus Interpreted Languages 48 Running CGI Scripts from the Command Line 49 Using Print Statements for Debugging 50 Summary 50 Q&A 51 Workshop 51 Quiz 51 Exercises 52 Quiz Answers 52 4Writing Your First CGI Program 53 Parts of CGI Programs 54 A Sample CGI Program 54 A URL-Redirection Program 57 How File Redirection Works 59 Pipes 60 vi Sams Teach Yourself CGI in 24 Hours 00 0672324040 FM 8/26/02 11:04 AM Page vi www.it-ebooks.info Working with Files in Perl 61 Common Statements Used in Perl 63 The if Statement 65 Perl Expressions 66 Summary 68 Q&A 68 Workshop 69 Quiz 69 Exercises 69 Quiz Answers 69 Part II Capturing User Input 71 5Creating HTML Forms 73 The <form> Tag 74 The action Attribute 74 The method Attribute 75 The enctype Attribute 75 The target Attribute 75 The <input> Tag 76 Text Input Fields 76 Password Fields 77 Check Boxes 78 Radio Buttons 78 Hidden Fields 79 File Upload Fields 80 Reset Buttons 80 Submit Buttons 80 Using Images as Submit Buttons 81 Other Form Fields 82 Text Areas 83 Select Lists 84 Workshop: Building an Entire Form 85 Elements in the Survey Form 87 Summary 87 Q&A 88 Workshop 88 Quiz 88 Exercises 88 Quiz Answers 89 Contents vii 00 0672324040 FM 8/26/02 11:04 AM Page vii www.it-ebooks.info 6Working with HTTP 91 HTTP Basics 92 What Takes Place During an HTTP Session 92 Step 1: Establish a TCP Connection 93 Step 2: The Web Browser Sends a Command to the Server 94 Step 3: The Web Browser Sends Request Headers 95 Step 4: The Web Server Responds 95 Step 5: The Web Server Sends Response Headers 96 Step 6: The Web Server Sends the Data to the Browser 96 Step 7: The Web Server Closes the TCP Connection 96 Request Methods 97 The GET Method 97 The POST Method 98 Choosing Between GET and POST 98 Server Response Codes 99 Response Headers 101 Cache-control 101 Content-length 101 Content-type 101 Expires 101 Pragma 102 Server 102 Set-Cookie 102 NPH Scripts 102 Content Types 103 How Servers Use Content Types 104 Content-Type Categories 105 Nonstandard Types 106 Secure Connections 107 Summary 108 Q&A 109 Workshop 109 Quiz 109 Exercises 109 Quiz Answers 110 7Validating User Input 111 Using JavaScript for Form Validation 111 How JavaScript Works to Validate Forms 112 An Example of Form Validation 113 The Form Itself 113 The Event Handler 114 Designing Easily Validated Forms 114 viii Sams Teach Yourself CGI in 24 Hours 00 0672324040 FM 8/26/02 11:04 AM Page viii www.it-ebooks.info Incorporating Validation into the Form-Processing Code 115 How a Form-Processing Program Works 115 An Example of Form Processing 116 The Main Script Logic 117 The Input Validation Subroutine 118 The Output Subroutine 119 The Form Creation Subroutine 120 The Full Source Code 121 Validating Values 123 Regular Expressions 124 An Example That Uses Regular Expressions 126 Summary 128 Q&A 128 Workshop 128 Quiz 128 Exercises 129 Quiz Answers 129 8Creating an Email Feedback Form 131 What Kinds of Applications Involve Sending Email? 132 How Email Works 132 Mail Message Composition 134 Using Net::SMTP 135 Example: Sending Email from a CGI Script 136 Setting Things Up 138 The Application Logic 139 Validating the Form 140 Sending the Email Message 141 Using sendmail 141 Using sendmail with Perl 142 Summary 143 Q&A 144 Workshop 144 Quiz 145 Exercises 145 Quiz Answers 145 Part III CGI Programming Languages and Tools 147 9Web Application Architecture 149 Application Design 150 Round-trip Scripts 150 Figuring Out Whether a Form Was Submitted 151 Declarative Programming 152 Contents ix 00 0672324040 FM 8/26/02 11:04 AM Page ix www.it-ebooks.info [...]... Good luck! www.it-ebooks.info PART I An Introduction to CGI Hour 1 Overview of CGI Programming 2 Setting Up Your CGI Environment 3 Downloading, Installing, and Debugging CGI Scripts 4 Writing Your First CGI Program www.it-ebooks.info www.it-ebooks.info HOUR 1 Overview of CGI Programming Do you use the World Wide Web to look up the latest stock quotes? Do you purchase items from online stores? Have you... webdev@samspublishing.com Mail: Mark Taber Associate Publisher Sams Publishing 800 East 96th Street Indianapolis, IN 4 6240 USA Reader Services For more information about this book or others from Sams Publishing, visit our Web site at www.samspublishing.com Type the ISBN (excluding hyphens) or the title of the book in the Search box to find the book you’re looking for www.it-ebooks.info www.it-ebooks.info... concepts behind software design in order to write useful programs in Perl www.it-ebooks.info 2 Sams Teach Yourself CGI in 24 Hours My goal in this book is to explain the Perl concepts that I use in the example programs, and not to go beyond that I also used as few special Perl features as possible in order to apply the lessons in these examples to the programming language that you use to write CGI programs...x Sams Teach Yourself CGI in 24 Hours Handling Many Types of Requests 153 Sharing Code Among Scripts 156 Using CGI: :Application 158 Installing CGI: :Appliction 159 Creating CGI: :Application Applications 162 An Example That Uses CGI: :Application 162 Other CGI: :Application Notes 166 Summary ... 187 CGI. pm www.it-ebooks.info Contents 11 Other Popular CGI Programming Languages xi 189 Will My Favorite Language Work for CGI? 189 Writing CGI Programs Using the Bourne Shell 190 How Shell Scripts Work 191 Creating Gateways to UNIX Commands 192 Working with Query Strings 193 Writing a Program That Uses the Query String 194 Writing CGI Programs in C ... 221 The Apache mod_perl Module 222 Porting Your Scripts from CGI to mod_perl 223 Summary 224 Q&A 224 Workshop 225 Quiz 225 Exercises 225 Quiz Answers 225 www.it-ebooks.info xii Sams Teach Yourself CGI in 24 Hours Part IV Building Basic CGI Applications 227 13 Using Flat Files for Data Storage 229 What Is a Database?... also point out that most of the examples in this book are written in Perl Perl is a scripting language that’s available for most computing platforms, including Unix and Windows It has a number of features that make it well-suited to CGI programming, and in fact, it’s the most popular language for writing CGI programs The biggest advantage for readers of this book is that it’s easy to learn Perl in bits... Overview of CGI Programming CGI Programming Languages As I’ve already stated, almost any programming language can be used to write CGI programs Just because it isn’t mentioned here doesn’t mean that it’s unsuitable for CGI programming As long as programs written in the language can meet the criteria that I discussed earlier in this hour for CGI programs, it can be used for CGI programming In this section... 394 Quiz Answers 394 Part VI Additional CGI Tips and Tricks 395 21 Handling Other Content Types 397 Content Types 397 Handling Binary Content 398 An Authenticated Download Application 399 www.it-ebooks.info xvi Sams Teach Yourself CGI in 24 Hours Creating Your Own Ad Server 403 Tracking User Activity 405 Summary 409 Q&A... application development platform In this book, you will learn how to build interactive Web applications using the Common Gateway Interface (CGI) —which is the predominant platform for deploying Web applications today www.it-ebooks.info 6 Hour 1 This hour will provide the introductory and background information you need before you can start writing CGI programs The following topics will be discussed: • . www.it-ebooks.info 800 East 96th St., Indianapolis, Indiana, 4 6240 USA Teach Yourself in 24 Hours Rafe Colburn CGI SECOND EDITION 00 0672 3240 40 FM 8/28/03. 8/28/03 9:41 AM Page i www.it-ebooks.info Sams Teach Yourself CGI in 24 Hours, Second Edition Copyright  2003 by Sams Publishing All rights reserved. No part