Webmaster in a Nutshell, Second Edition

Chapter 12. CGI Overview

The Common Gateway Interface (CGI) is an essential tool for creating and managing comprehensive web sites. With CGI, you can write scripts that create interactive, user-driven applications.

CGI allows the web server to communicate with other programs that are running on the server. For example, with CGI, the web server can invoke an external program, while passing user-specific data to the program (such as what host the user is connecting from, or input the user has supplied through an HTML form). The program then processes that data, and the server passes the program’s response back to the web browser.

Rather than limiting the Web to documents written ahead of time, CGI enables web pages to be created on the fly, based upon the input of users. You can use CGI scripts to create a wide range of applications, from surveys to search tools, from Internet service gateways to quizzes and games. You can count the number of users who access a document or let them sign an electronic guestbook. You can provide users with all types of information, collect their comments, and respond.

Teaching CGI programming from scratch is beyond the scope of this book—for that, we recommend O’Reilly’s upcoming CGI Programming with Perl, by Shishir Gundavaram and Gunther Birznieks.

This chapter through Chapter 15 summarize the essential components of CGI:

• This chapter gives a quick introduction to the mechanism of CGI and lists the environment variables commonly defined by servers ...