But for more advanced processing, such as collecting data into a file or database, or retrieving information and sending it back, or doing some calculations with the submitted data, you will probably need to write a server-side script of your own. CGI is simply an interface between HTML forms and server-side scripts. But CGI is widely used and useable. What we discuss here is how it works. The often-mysticized abbreviation CGI , for Common Gateway Interface , refers just to a convention on how the invocation and parameter passing takes place in detail.
Invocation means different things in different cases.
For a Perl script, the server would invoke a Perl interpreter and make it execute the script in an interpretive manner. For an executable program, which has typically been produced by a compiler and a loader from a source program in a language like C, it would just be started as a separate process. Although the word script typically suggests that the code is interpreted, the term CGI script refers both to such scripts and to executable programs. The filename extension .cgi has no fixed meaning in general. It depends on the scripting or programming language used how a program can access the value of an environment variable.