4.1 CGI

http://hoohoo.ncsa.uiuc.edu/cgi/overview.html

The Common Gateway Interface, or CGI, is an interface for running external programs, or gateways, under an HTTP information server. What is referred to as gateway are really programs which handle information requests and return the appropriate document or generate documents on the fly.

Gateway programs, or scripts, are executable programs which can be run by themselves. Users normally start a CGI program on the web server by sending a request to the server. The server then processes this request by executing the CGI program, while the browser on the client site waits until the program has been completed and the output has been sent back to the client. A sample application might be to connect a database to the World Wide Web to allow people from all over the world to query it. The database provider then needs to create a CGI program that the Web demon will execute to transmit information to the database engine, and receive the results back and display them on the client.

Gateways conforming to the CGI specification can be written in any language which produces an executable file. Examples include C and FORTRAN programs, PERL scripts, Bourne and C shell scripts, AppleScript, Visual Basic, Tcl, etc..