.CGI File Extension

A CGI file is a shared gateway interface script used by a web server to run an external program to process client requests. The script is stored in a file with a .cgi extension and is usually written in Perl or C programming languages. These were introduced from the early days of the Web when Web developers wanted to connect databases to their Web servers. A server that maintained a standard gateway between the Web server and the databases was suitable for running CGI code.

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The web server uses CGI scripts to make it easier for the owner to customize how the URL will be handled. This procedure is usually done by marking the new directory (where the documents are mainly located) as containing CGI scripts; its commonly known name is CGI-bin. When a web browser requests a URL saying the file in the CGI directory, instead of just sending that file to the web browser, the HTTP server executes the specified script and returns the script's output to the web browser. In short, whatever the CGI script sends to the standard output is passed to the Web client, not displayed in the terminal window.

Be sure to double-check the file extension to make sure you don't confuse a CGM (Computer Graphics Metafile), CSI, CGR (CATIA Graphical Representation), CGF (Crytek Geometry Format), or CGZ (Cube Map) file with one that has a CGI extension. As you can see, the file extensions used in different formats may look the same, but that does not necessarily mean that they open or convert similarly.