Introduction to the CGI

What is it?

The Common Gateway Interface, or CGI, is an interface for running external programs, or gateways, under an information server. Currently, the supported information servers are HTTP servers.

What's a gateway used for?

What we refer to as gateways are really programs which handle information requests and return the appropriate document or generate a document on the fly. The ability to generate documents on the fly, such as being able to generate a finger request and convert the result to HTML, is what we refer to as gatewaying.

Gateways can be used for a variety of purposes, the most common being the handling of ISINDEX and FORM requests for HTTP.

What are gateway programs?

Gateway programs, or scripts, are executable programs which can be run by themselves (but you wouldn't want to). They have been made external programs in order to allow them to run under various (possibly very different) information servers interchangably.

What language can I write these gateways in?

Gateways conforming to this specification can be written in any language which produces an executable file. Examples include C programs, PERL scripts, Bourne shell scripts, and C shell scripts, with many others.

Who came up with it?

The specification was discussed between the main HTTP server authors. Credits go to:

as well as countless others.

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Rob McCool robm@ncsa.uiuc.edu