Writing Perl Modules for CPAN

Nov 6, 2002 by Simon Cozens

As Andy Lester points out in this month’s Perl Review, one big advantage of there being so many Perl books around is that the publishers can now get around to putting out books on some of the more “niche” areas of Perl. Finally, we can explore many areas that haven’t really been written down and codified before.

Sam Tregar’s “Writing Perl Modules For CPAN” certainly does this, and in a good way; most hints and strategies for designing, creating and maintaining Perl modules, including the sometimes arduous community interaction that this entails, have been handed down wordlessly through observation of the old hands. I tried my best in the core perlnewmod documentation to explain some of the issues involved, but Sam - a bit of an old hand himself, with the HTML::Template and Devel::Profiler modules amongst his output - takes the time to cover all the bases: from how to create a module distribution and how to get your PAUSE ID and so on to how to handle feature creep, setting up mailing lists and CVS servers, and with “bonus” chapters on XS programming and CGI applications.

Don’t be put off by the book’s title; even if you’re not planning on making your modules public, we’ve found that the techniques of good distribution management and source control explained in this book are assets even when you’re developing modules internal to a company or specific application.

Frequent readers of my reviews will know that one of my favorite subjects is introductory filler, and this book doesn’t get off lightly either; chapter 1, the history and motivation of the CPAN, really ought to go in the foreword, and chapter 2, Perl module basics, should be required knowledge.

The writing style is friendly but direct, although I occasionally feel that the author tends to overuse footnotes a little, (Chapter 7 has 25 footnotes in 10 pages) and has a good mix of practical and philosophical discussion appropriate for this topic. The code style is perfectly fine, although I would like to have seen use strict a little more prominently, and some discussion of error handling and checking would not have gone amiss.

On the down side: typography. For some reason, the book’s designer is enamoured of bold and italic typewriter faces for headings, which frankly looks horrible. Sadly, typos are rife, and there are some surprising omissions, too: The wonderful cpan-upload script is not mentioned, nor is the CPAN bug-tracking system, and coverage of testing, one of the recent obsessions of the Perl module community, is quite thin.

On the other hand, I was surprised by the XS chapters; they work. Sam somehow manages to pack just enough information into two relatively slim chapters at the end of the book to allow some pretty complex XS modules to be created by the adventurous reader, but then follows it with quite a bit of repetition in the following chapter, on Inline::C.

Similarly, the chapter on Great CPAN Modules was an unexpectedly good read - I’d never before sat down and thought about why one particular XML parsing module (say) should be more popular than another, and this is a good summary of the issues involved.

If you’re thinking about writing a Perl module, whether or not it’s for public consumption, then I’d certainly recommend getting a copy of this book; I certainly learned a few things about module maintainance from it, and I’m sure you will too.

Writing Perl Modules for CPAN is published by Apress.