The next step in your evolution as a
CGI programmer is to learn how to customize scripts for your own
needs. Thus, the first task is to understand how CGI programs
are structured.
Many CGI programs use a common toolbox
of routines-called libraries. Thus, it is helpful to understand
how libraries work
Web applications are not ferocious.
After a bit of delving into the lines of code, you'll often find
that a well-written program can be tame.
It's a good idea to view programs as a
group of associated algorithms (or routines), all of which have
small, well-defined functions. Algorithms are like ants in an
ant colony, each doing one small job well.
To decipher a program, you need only
focus on understanding how these simple packets of code, called
subroutines, interact. With practice, they will call out to
you: "I add numbers," "I gather form input," "I parse that
input," "I say hello world when asked." If you understand the
program one routine at a time, the application's design will
emerge and you will be more comfortable modifying and adding to
the original program.
There are three types of algorithms
that you will be faced with in most Perl CGI applications:
individual algorithms, application-specific subroutines, and
interapplication libraries. Let's look at each of these
types.
