Web Performance Tuning

Chapter 15. CGI Programs

While plain HTML documents stored on your web server can contain whatever text you like, that text is static. Everyone who requests that document through a web browser will get exactly the same document. Quite often, however, you’d like to customize the response for a particular user. For example, a retail chain might want to query a database for the user and return the address of the branch store nearest the user. One way to do this is to have the web server run a program that will query the database and format the result in HTML. The first widely available method for incorporating dynamic content like this into web pages was the Common Gateway Interface (CGI) standard. CGI was introduced as part of the web server developed at the National Center for Supercomputing Applications (NCSA).

CGI provides a standard interface between web servers and programs that can generate HTML or other web content. CGI got its start as a literal gateway between web servers and older Unix programs that send their output to the terminal, but it quickly became clear that the real value of CGI was that it could provide a web interface to almost any software. Programs started by the web server using the CGI interface are referred to as CGI programs, or just CGIs, though CGI is technically the interface and not the programs that use the interface.

The definitive description of CGI 1.1, the current version, is on the Web at http://hoohoo.ncsa.uiuc.edu/cgi/. From here on, I will assume ...