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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.
Module::Starter comes in handy. It provides
a simple, command-line tool to create a skeleton module quickly and
Before we can build our module, we need to install
from the CPAN.
Module::Starter allows us to choose from a variety
of build frameworks, from the aging
comes standard with Perl, you may need to install the other build
frameworks. At Perl Training Australia we generally use
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@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
Module::Install as our build-system, instead of
Once this is done, you should have a
My-Module directory with a
skeleton module inside.
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
$ 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:
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.
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.
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.
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
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
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.
The lib/ directory will contain your skeleton module, and is
where you'll be doing much of your work.
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.
The t/ directory contains all the tests that will be executed
when you run a
make test. By default,
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
Test::Tutorial at http://search.cpan.org/perldoc.
At Perl Training Australia, we usually add a test based on
to encourage good coding practices, and
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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