Perl for Web Site Management

Chapter 16. Writing Perl Modules

It’s time we learned how to share code across more than one of our scripts by creating our own Perl modules. This sort of code sharing is a really good idea. We’ve already seen how helpful it can be to take some block of code that is going to be used multiple times in a script and put it into its own subroutine. In the same vein, it’s helpful to take common code that is going to be used in multiple scripts and put it into a module that can be shared by all of them.

The typical beginner’s approach to sharing code is to just use copy-and-paste, which is, of course, a problem waiting to happen. Eventually you’ll want to update that code to fix a bug or add some new capability. When that happens, you’ll have to choose between updating one copy and leaving others in the old state (which is bad), or making the same changes over and over again (which is also bad, though in a different way).

Modules are the solution. I felt kind of intimidated when I started writing my own modules. I’m not sure why; I guess in my newbiehood I had such a high opinion of Perl’s standard and CPAN modules that I was reluctant to pry the lid off those black boxes and try to construct my own. But in retrospect, I didn’t have anything to be worried about. Most of it is very straightforward, and the deeper parts can be safely ignored as long as you’re careful to invoke the magic properly.

This chapter explains everything you need to know to start writing your own Perl modules. It ...