If you use a programming language like C or Fortran, the source code must be compiled before it will run. Many people prefer to write CGI scripts instead of programs, since they are easier to debug, modify, and maintain than a typical compiled program. If you have no idea what CGI is, you should read this introduction . Once you have a basic idea of what CGI is and what you can use it for, you should read this primer which will help you get started writing your own gateways. If you are interested in handling the output of HTML forms with your CGI program, you will want to read this guide to handling forms with CGI programs .
Security is a crucial issue when writing CGI programs.
Please read these tips on how to write CGI programs which do not allow malicious users to abuse them. When you get more advanced, you should read the interface specification which will help you utilize CGI to the fullest extent. If you are a server software author, it will help you add CGI compliance to your information server. There is now also a tutorial for writing ErrorDocument handling CGI scripts. Examples of CGI behavior and programs You may wish to look at this page of examples which demonstrate how the client URL affects the interface variables.