Web Design in a Nutshell, 3rd Edition

CGI (Common Gateway Interface)

Instead of pointing to an HTML file, a URL may request that a CGI program be run. CGI stands for Common Gateway Interface, and it’s what allows the web server to communicate with other programs (CGI scripts ) that are running on the server. CGI scripts are commonly written in the Perl, C, or C++ language.

CGI scripts are the traditional methods for performing a wide variety of functions such as searching, server-side image map handling, and gaming; however, their most common use is form processing (information entered by the user through entry fields in the document). As other more powerful options for interfacing with databases become available (such as ASP, PHP, and Java servlets ), traditional CGI programming is getting less attention.

Most server administrators follow the convention of keeping CGI scripts in a special directory named cgi-bin (short for CGI-binaries). Keeping them in one directory makes it easier to manage and secure the server. When a CGI script is requested by the browser, the server runs the script and returns the dynamic content it produces to the browser.