CGI program

World-Wide Web (Often "CGI script") A program running on a

web server to produce dynamic content, usually an HTML

web page, in response to a user's request.

The Common Gateway Interface specification defines the

interface between the web server and such programs. The

program can access any data that a normal application program

can, however the facilities available to CGI programs are

usually limited for security.

Although CGI programs can be compiled programs, they are more

often written in a (semi) interpreted language such as

Perl, or as Unix shell scripts, hence the name "CGI

script".

Here is a trivial CGI script written in Perl. (It requires

the "CGI" module available from CPAN).

#!/usr/bin/perl

use CGI qw(:standard);

print header, start_html,

h1("CGI Test"),

"Your IP address is: ", remote_host(),

end_html;

When run it produces an HTTP header and then a simple HTML

page containing the IP address or hostname of the machine

that generated the initial request. If run from a command

prompt it outputs:

Content-Type: text/html

!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN"

HTMLHEADTITLEUntitled Document/TITLE

/HEADBODYH1CGI Test/H1Your IP address is:

localhost/BODY/HTML

The CGI program might be saved as the file "test.cgi" (or

test.pl) in the appropriate directory on a web server,

e.g. "/home/httpd/cgi-bin/".

A user could then type the appropriate URL,

e.g. http://www.acme.com/cgi-bin/test.cgi, into their webbrowser to get the program to run and a custom page produced

for them.

Early web servers required all CGI programs to be installed in

one directory called cgi-bin but it is much better to keep

them with the HTML files to which they relate unless they are

truly global to the site. All modern web servers make this

easy to do.

(2000-06-23)