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The first edition of CGI Programming on the World Wide Web was published in early 1996. The Web was very different then: the number of web hosts was 100,000, Netscape Navigator 2.0 (the first JavaScript-enabled browser) was released, and Java was less than a year old and was used primarily for applets. The Web was still young, but it was developing quickly.

In 1996, CGI was the only stable and well-understood method for creating dynamic content on the Web. However, very few sites exploited its full potential. In the first edition, Shishir wrote:

Today's computer users expect custom answers to particular questions. Gone are the days when people were satisfied by the computing center staff passing out a single, general report to all users. Instead, each salesperson, manager, and engineer wants to enter specific queries and get up-to-date responses. And if a single computer can do that, why not the Web?

This is the promise of CGI. You can display sales figures for particular products month by month, as requested by your staff, using beautiful pie charts or plots. You can let customers enter keywords in order to find information on your products.

In 1996, these were bold claims. Today, they describe business as usual. That promise of CGI has certainly been fulfilled.

This book is about more than writing CGI scripts. It is about programming for the Web. Although we focus on CGI programming with Perl (thus the title change for this edition), many of the concepts we cover are common to all server-side web development. Even if you find yourself working with alternative technologies down the road, the effort you invest learning CGI now will continue to yield value later.

0.1. What's in the Book

Because CGI has changed so much in the last few years, it is only appropriate that this new edition reflect the changes. Thus, most of this book has been rewritten. New topics include, HTML templates, security, JavaScript, XML, search engines, style suggestions, and compatible, high-performance alternatives to CGI. Previous topics, such as session management, email, dynamic images, and relational databases, have been expanded and updated. Finally, we modified our presentation of CGI to begin with a discussion of HTTP, the underlying language of the Web. An understanding of HTTP provides a foundation for a more thorough understanding of CGI.

Despite the changes, the original goal of this book remains the same: to teach you everything you need to know to become a good CGI developer. This is not a learn-by-example book -- it isn't built around a handful of CGI scripts with a discussion of how each script works. There are already lots of books like that available for CGI. While these books can certainly be useful, especially if one of the examples matches a particular challenge you are facing, they often teach how without explaining why. The aim of this book is to cover the fundamentals so that you can create CGI scripts to tackle any challenge. Don't worry, though, because we'll look at lots of examples. But our examples will serve to illustrate the discussion, rather than the other way around.

We should admit up front that there is a Unix bias in this book. Both Perl and CGI were originally conceived for the Unix platform, so it remains the most popular platform for Perl and CGI development. Of course, Perl and CGI support numerous other systems, including Microsoft's popular 32-bit Windows systems: Windows 95, Windows 98, Windows NT, and Windows 2000 (hereafter collectively referred to as Win32 ). Throughout this book, we will focus on Unix, but we'll also point out those things you need to be aware of when developing for non-Unix-compatible systems.

We use the Apache web server throughout our examples. There are several reasons: it is the most popular web server used today, it is available for the most platforms, it is free, it is open source, and it supports modules (such as mod_perl and mod_ fastcgi) that improve both the power and the performance of Perl for web development.

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