CGI and Object Oriented Perl: Background

By a wide margin, the most popular trend in modern programming (straight from the catwalks of Paris) is object-oriented programming. Perl has jumped onto the "OOP" bandwagon, as it is known, beginning with Perl 5. Some programmers swear by object-oriented programming while others loathe it; Perl allows for either, in that OOP is there for those who want to use it but not necessary for those who don't. Taken in the right spirit, though, object-oriented programming can make life easier.

As a web developer primarily interested in using a Perl as a tool, you'll mostly deal with OOP as a user of objects, rather than a creator of objects. That's good -- using objects in Perl is no more complicated than anything else we've seen in Part 1 of this introduction.

First, what is an object? Very simply and vaguely put: an object is "a thing which does stuff". This isn't as meaningless as it sounds. Consider your kitchen stove. It is an object. The stove has a number of characteristics and a number of actions that it is capable of. Its characteristics, which we could call properties, include its size, its color, how many burners it has, the temperature ranges it can reach, and so on. The stove also can perform various actions -- it can heat one or more burners to varying degrees, it can heat the inner cavity and maintain a certain temperature, etc.

When you use a stove, though, you interact with it through a simple interface; the interface translates your requests into actions that the stove takes care of on its own. Thus, you simply turn a knob to 350 and the stove knows what to do from there. This is how Perl objects behave. Objects in Perl typically return a result from their actions (one could say that the stove also returns a result: heat).

The most commonly used object by web developers coding in Perl is undoubtedly the CGI object. So, we can tackle both the topic of OOP and a starter on CGI at once with a look at the CGI object in Perl.

Perl objects are contained within modules, and modules are hunks of Perl which contain one or more miniature tools that you can use. You can literally think of modules as toolboxes within Perl. The standard Perl distribution includes many of the most popular modules, but you must specify at the start of your program which modules you would like to use.

#!/usr/bin/perl

use CGI;

In the above embryonic Perl program, the use statement names the module we would like to access from this program. We happen to know that the CGI module contains the CGI object (the resource list at the end of this article contains links to information on other modules).

Perl Pattern Matching: Regular Expressions
The Perl You Need to Know
Notes on Running CGI