!name: CGI
                 The Norton Guide To ClipX.Lib Version 1.2
                               What Is CGI
                    
Overview

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The Common Gateway Interface (CGI) is a standard for interfacing external 
applications with information servers, such as HTTP or Web servers. A plain 
HTML document that the Web daemon retrieves is static, which means it exists 
in a constant state: a text file that doesn't change. A CGI program, on the 
other hand, is executed in real-time, so that it can output dynamic 
information.  For example, let's say that you wanted to "hook up" your Unix 
database to the World Wide Web, to allow people from all over the world to 
query it. Basically, you need to create a CGI program that the Web daemon 
will execute to transmit information to the database engine, and receive the 
results back again and display them to the client. This is an example of a 
gateway, and this is where CGI, currently version 1.1, got its origins. 

The database example is a simple idea, but most of the time rather difficult 
to implement. There really is no limit as to what you can hook up to the Web. 
The only thing you need to remember is that whatever your CGI program does, 
it should not take too long to process. Otherwise, the user will just be 
staring at their browser waiting for something to happen. 


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Specifics

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Since a CGI program is executable, it is basically the equivalent of letting 
the world run a program on your system, which isn't the safest thing to do. 
Therefore, there are some security precautions that need to be implemented 
when it comes to using CGI programs. Probably the one that will affect the 
typical Web user the most is the fact that CGI programs need to reside in a 
special directory, so that the Web server knows to execute the program rather 
than just display it to the browser. This directory is usually under direct 
control of the webmaster, prohibiting the average user from creating CGI 
programs. There are other ways to allow access to CGI scripts, but it is up 
to your webmaster to set these up for you. At this point, you may want to 
contact them about the feasibility of allowing CGI access. 

If you have a version of the NCSA HTTPd server distribution, you will see a 
directory called /cgi-bin. This is the special directory mentioned above where 
all of your CGI programs currently reside. A CGI program can be written in any 
language that allows it to be executed on the system, such as: 

C/C++ 
Clipper    ( I couldn't resist )
Fortran 
PERL 
TCL 
Any Unix shell 
Visual Basic 
AppleScript 

It just depends what you have available on your system. If you use a 
programming language like C or Fortran, you know that you must compile the 
program before it will run. If you look in the /cgi-src directory that came 
with the server distribution, you will find the source code for some of the 
CGI programs in the /cgi-bin directory. If, however, you use one of the 
scripting languages instead, such as PERL, TCL, or a Unix shell, the script 
itself only needs to reside in the /cgi-bin directory, since there is no 
associated source code. Many people prefer to write CGI scripts instead of 
programs, since they are easier to debug, modify, and maintain than a typical 
compiled program.                             

This information was obtained from:

Online reference: NCSA