introduction to web programming Using Libraries 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.

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