Common Gateway Interface

In computing, Common Gateway Interface (CGI) is an interface specification that enables web servers to execute an external program to process HTTP/S user requests. Such programs are often written in a scripting language and are commonly referred to as CGI scripts, but they may include compiled programs. A typical use case occurs when a web user submits a web form on a web page that uses CGI. The form's data is sent to the web server within an HTTP request with a URL denoting a CGI script. The web server then launches the CGI script in a new computer process, passing the form data to it. The output of the CGI script, usually in the form of HTML, is returned by the script to the Web server, and the server relays it back to the browser as its response to the browser's request. Developed in the early 1990s, CGI was the earliest common method available that allowed a web page to be interactive. Due to a necessity to run CGI scripts in a separate process every time the request comes in from a client various alternatives were developed. In 1993, the National Center for Supercomputing Applications (NCSA) team wrote the specification for calling command line executables on the www-talk mailing list. The other Web server developers adopted it, and it has been a standard for Web servers ever since. A work group chaired by Ken Coar started in November 1997 to get the NCSA definition of CGI more formally defined. This work resulted in RFC 3875, which specified CGI Version 1.1. Specifically mentioned in the RFC are the following contributors: Rob McCool (author of the NCSA HTTPd Web server) John Franks (author of the GN Web server) Ari Luotonen (the developer of the CERN httpd Web server) Tony Sanders (author of the Plexus Web server) George Phillips (Web server maintainer at the University of British Columbia) Historically CGI programs were often written using the C programming language. RFC 3875 "The Common Gateway Interface (CGI)" partially defines CGI using C, in saying that environment variables "are accessed by the C library routine getenv() or variable environ".