Starting a module with Module::Starter

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Starting a new module can be a lot of work. A good module should have a build system, documentation, a test suite, and numerous other bits and pieces to assist in its easy packaging and development. These are useful even if we never release our module to CPAN.

Setting this up can be a lot of work, especially if you've never done it before. While the h2xs tool that comes with Perl will do some of this for you, it's showing its age, and doesn't allow us to take advantage of recent tools. We want to spend our time writing code, not trying to decode our build system.

That's where Module::Starter comes in handy. It provides a simple, command-line tool to create a skeleton module quickly and easily.

Using module-starter

Before we can build our module, we need to install Module::Starter from the CPAN. Module::Starter allows us to choose from a variety of build frameworks, from the aging ExtUtils::MakeMaker to Module::Install and Module::Build. While ExtUtils::MakeMaker comes standard with Perl, you may need to install the other build frameworks. At Perl Training Australia we generally use Module::Install.

Creating a module with Module::Starter couldn't be easier. On the command line we simply write:

    module-starter --module=My::Module --author="Jane Smith"
        --email=jane.smith@example.com --builder=Module::Install

The module name, author, and e-mail switches are all required. We've used the optional --builder switch to specify we want to use Module::Install as our build-system, instead of the default ExtUtils::MakeMaker.

Once this is done, you should have a My-Module directory with a skeleton module inside.

A skeleton tour

If you've never created a module before, or you've been making them by hand, then it's nice to take a look at what you get for your Module::Starter skeleton.

    $ ls -la

    total 8
    drwxr-xr-x   4 pjf pjf    0 Jul  4 16:59 .
    drwxr-xr-x  51 pjf pjf    0 Jul  4 16:59 ..
    -rw-r--r--   1 pjf pjf   96 Jul  4 16:59 .cvsignore
    -rw-r--r--   1 pjf pjf  109 Jul  4 16:59 Changes
    -rw-r--r--   1 pjf pjf   90 Jul  4 16:59 MANIFEST
    -rw-r--r--   1 pjf pjf  183 Jul  4 16:59 Makefile.PL
    -rw-r--r--   1 pjf pjf 1378 Jul  4 16:59 README
    drwxr-xr-x   3 pjf pjf    0 Jul  4 16:59 lib
    drwxr-xr-x   2 pjf pjf    0 Jul  4 16:59 t

Let's look at each of these files in turn:

.cvsignore

Module::Starter assumes you'll be using CVS for revision control, and provides a .cvsignore file with the names of files that are auto-generated and not to be tracked with revision control. At Perl Training Australia we use git for new projects, and so we rename this to .gitignore.

(As of version 1.52, this file is now called "ignores.txt", so you can use it however you like.)

Changes

This is a human-readable file tracking module revisions and changes. If you're going to release your code to the CPAN, it's essential for your users to know what has changed in each release. Even if you're only using your code internally, this is a good place to document the history of your project.

MANIFEST

The MANIFEST file tracks all the files that should be packaged when you run a make tardist to distribute your module. Normally it includes your source code, any file needed for the build system, a META.yml that contains module meta-data (usually auto-generated by your build system), tests, documentation, and anything else that you want your end-user to have.

If you don't want to manually worry about adding entries to the MANIFEST file yourself, most build systems (including Module::Install) allow you to write make manifest to auto-generate it. For this to work, you'll want to make a MANIFEST.skip file which contains filenames and regular expressions that match files which should be excluded from the MANIFEST.

Makefile.PL

This is the front-end onto our build system. When we wish to build, test, or install our module, we'll always invoke Makefile.PL first:

    perl Makefile.PL
    make
    make test
    make install

Most build systems will provide a make tardist target for building a tarball of all the files in our MANIFEST, a make disttest for making sure our tests work with only the MANIFEST listed files, and make clean and make distclean targets for clearing up auto-generated files, including those from the build system itself if a make distclean is run.

You'll almost certainly wish to customise your Makefile.PL a little, especially if your module has dependencies. You'll want to consult your build system documentation for what options you can uses. For Module::Install this documentation can be found at http://search.cpan.org/perldoc.

README

The README file should contain basic information for someone thinking of installing your module. Mentioning dependencies, how to build, and how to find/report bugs are all good things to mention in the README file. Some systems (including the CPAN) will extract the README and make it available separate from the main distribution.

lib/

The lib/ directory will contain your skeleton module, and is where you'll be doing much of your work. Module::Starter will have already added some skeleton documentation, a version number, and some skeleton functions.

You can add more modules to the lib/ directory if you wish. Splitting a very large module into smaller, logical pieces can significantly improve maintainability.

t/

The t/ directory contains all the tests that will be executed when you run a make test. By default, Module::Starter will provide some simple tests to ensure that your module compiles, that you'll filled in relevant sections of the boilerplate documentation, and that your documentation covers all your subroutines and doesn't contain any syntax errors.

If you're new to testing in Perl, then you should start by reading the Test::Tutorial at http://search.cpan.org/perldoc.

At Perl Training Australia, we usually add a test based on Test::Perl::Critic http://search.cpan.org/perldoc to encourage good coding practices, and Test::Kwalitee http://search.cpan.org/perldoc to catch common mistakes that are made in distributions.

Ideally when developing your module, the more tests you have, the better. If you already have a test suite and you're wondering which parts of your code are not being tested, you can use the excellent Devel::Cover tool from http://search.cpan.org/perldoc.

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