CGI Programming

CGI" stands for "Common Gateway Interface." CGI is the method by which a web server can obtain data from (or send data to) databases, documents, and other programs, and present that data to viewers via the web. More simply, CGI is programming for the web. A CGI can be written in any programming language, but Perl is the most popular, and for the course of this book, Perl is the language we'll be using.If you're going to create web pages, then at some point you'll want to add a counter, a form to let visitors send you mail or place an order, or something similar.

CGI enables you to do that and much more. From mail-forms and counter programs, to the most complex database scripts that generate entire websites on-the-fly, CGI programs deliver a broad spectrum of content on the web today. If you've ever looked at a site such as Amazon.com, DejaNews, or Yahoo, and wondered how they did it... the answer is CGI. CGI experience is also in high demand from employers now; you could substantially improve your salary and job prospects by learning CGI.

A CGI program is still a Perl script. Perl is a simple language, easy to learn, yet powerful enough to accomplish the most difficult tasks. It is widely available, and is probably already installed on your Unix server. Perl is an interpreted language, meaning you don't need to compile your script - you simply write your script and run it (or have the web server run it). The script itself is just text code; the Perl interpreter does all the work. The advantage to this is you can copy your script with little or no changes to any machine with a Perl interpreter. The disadvantage is you won't discover any bugs in your script until you run it. You can edit your Perl scripts either on your local machine (using your favorite text editor - Notepad, Simpletext, etc.), or in the Unix shell.