from
The Free On-line Dictionary of Computing (8 July 2008)
Common Gateway Interface
cgi-bin
CGI program
CGI script
<World-Wide Web> (CGI) A {standard} for running external
{programs} from a {World-Wide Web} {HTTP} {server}. CGI
specifies how to pass {arguments} to the program as part of
the HTTP request. It also defines a set of {environment
variables} that are made available to the program. The
program generates output, typically {HTML}, which the web
server processes and passes back to the {browser}.
Alternatively, the program can request {URL redirection}. CGI
allows the returned output to depend in any arbitrary way on
the request.
The CGI program can, for example, access information in a
{database} and format the results as HTML. The program can
access any data that a normal application program can, however
the facilities available to CGI programs are usually limited
for security reasons.
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 common 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; charset=ISO-8859-1
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
lang="en-US" xml:lang="en-US">
<head>
<title>Untitled Document</title>
<meta http-equiv="Content-Type"
content="text/html; charset=iso-8859-1" />
</head>
<body>
<h1>CGI Test</h1>Your IP address is: localhost
</body>
</html>
The CGI program might be saved as the file "test.pl" in the
appropriate directory on a web server,
e.g. "/home/httpd/test".
Accessing the appropriate {URL}, e.g.
http://acme.com/test/test.pl, would cause the program to
run and a custom page produced and returned.
Early web servers required all CGI programs to be installed in
one directory called cgi-bin but it is better to keep them
with the HTML files to which they relate unless they are truly
global to the site. Similarly, it is neither necessary nor
desirable for all CGI programs to have the extension ".cgi".
Each CGI request is handled by a new process. If the process
fails to terminate for some reason, or if requests are
received faster than the server can respond to them, the
server may become swamped with processes. In order to improve
performance, {Netscape} devised {NSAPI} and {Microsoft}
developed the {ISAPI} standard which allow CGI-like tasks to
run as part of the main server process, thus avoiding the
overhead of creating a new process to handle each CGI
invocation. Other solutions include {mod_perl} and {FastCGI}.
Latest version: CGI/1.1.
(http://hoohoo.ncsa.uiuc.edu/cgi).
(2007-05-22)