When a CGI program is called, the information
that is made available to it can be roughly broken into three groups:
- Information about the client, server,
- Form data that the user supplied
- Additional pathname information
Most information about the client, server, or user is placed
in CGI environment variables. Form data is either incorporated into
an environment variable, or is included in the "body" of the request.
And extra path information is placed in environment variables.
See a trend here? Obviously, CGI environment variables are
crucial to accessing input to a CGI program. In this chapter, we
will first look at a number of simple CGI programs under UNIX
that display and manipulate input. We will show some examples that
use environment variables to perform some useful functions, followed
by examples that show how to process HTML form
input. Then we will focus our attention on processing this information
on different platforms.