CGI Programming with Perl

The Common Gateway Interface

• Describe computations



• Allow interaction with the user



• Provide access to a database

A request to run a CGI program is like any other HTTP request

except that the requested file can be identified by the server as being a CGI program

Identifying CGI by their address on the server or by their filename extensions

When a server receives a request for a CGI, it does not return the file, it executes it

The results of a CGI program execution can take many different forms

It could produce just the URL of an existing document

Most often an HTML document is returned

1. An HTTP header
   
   
   • If the document is going directly to the client, the header must be complete
   
   
   
   • If the document is going through the server, the header can be partial --it is completed by the server



2. A body which can be:
   
   
   • Plain text
   
   
   
   • HTML
   
   
   
   • image file
   
   
   
   • audio file

Common for users to interact with the server through forms

The browser presents a form to the user

The user is asked to fill in the boxes and to click the buttons of the form

The user submits the filled-in form by clicking the submit button on the form

The content of the form are encoded and transmitted to the server

The server must use a program to:

• Decode the transmitted form contents



• Perform whatever computation is necessary on the form data



• Produce its output

Both CGI programs and client-side scripts support dynamic documents

Client-side scripts cannot access files and databases on the server