how-to-add-the-license-field-to-meta-files-on-cpan.tt

=title How to add the license field to the META.yml and META.json files on CPAN?
=timestamp 2012-12-28T16:45:56
=indexes license, Perl, Perl 5, CPAN, META, ExtUtils::MakeMaker, Module::Build, Module::Install, Dist::Zilla, CPAN::Meta::Spec
=status show
=author szabgab
=index 1
=archive 1
=feed 1
=comments 1
=social 1

=abstract start

Every distribution on CPAN can include a META.yml and a META.json file.
They should hold the same information, META.json is just the newer format.
So you'll find a lot more distributions with only META.yml and you'll find
a few, probably very old distribution with no META file at all.

The META files can both have a field indicating the <b>license</b> of the distribution.

Having the license information in the META files makes it very easy for automated tools
to check if a set of modules have a certain set of licenses.

=abstract end

As the META files are usually generated automatically when the distribution is released
by the author, I am going to show you how you can tell the 4 main packaging systems
to include the license field.

In the examples  I'll use the most common, so called, <b>Perl</b> license:

<h2>ExtUtils::MakeMaker</h2>

If you are using <a href="https://metacpan.org/module/ExtUtils::MakeMaker">ExtUtils::MakeMaker</a> add the following to your Makefile.PL
as parameter in the <b>WriteMakefile</b> function:

<code lang="perl">
'LICENSE'  => 'perl',
</code>

If you want to make sure older versions of ExtUtils::MakeMaker won't give warnings on
unknown LICENSE field, you can use the following code:

<code lang="perl">
($ExtUtils::MakeMaker::VERSION >= 6.3002 ? ('LICENSE'  => 'perl', ) : ()),
</code>

<a href="http://search.cpan.org/src/NWCLARK/perl-5.8.8/lib/ExtUtils/MakeMaker.pm">The version distributed with perl 5.8.8 is 6.30</a>
thus it does not yet contain this feature. The best if you could upgrade ExtUtils::MakeMaker.

<h2>Module::Build</h2>

If you are using <a href="https://metacpan.org/module/Module::Build">Module::Build</a>, add the following to Build.PL,
in the Module::Build->new call:

<code lang="perl">
license               => 'perl',
</code>

<h2>Module::Install</h2>

If you are using <a href="https://metacpan.org/module/Module::Install">Module::Install</a> add the following to Makefile.PL:

<code lang="perl">
license        'perl';
</code>

<h2>Dist::Zilla</h2>

If you are using <a href="http://dzil.org/">Dist::Zilla</a>, just add the following entry to the dist.ini file:

<code lang="perl">
license = Perl_5
</code>

<h2>META specification</h2>

In order to check the current list of valid options for the license field,
check the <a href="https://metacpan.org/module/CPAN::Meta::Spec">CPAN::Meta specification</a>.

<h2>Copyright and Licensing</h2>

According to the <a href="http://www.perlfoundation.org/cpan_licensing_guidelines">CPAN Licensing Guidelines</a>
of The Perl Foundation, it is <b>required</b> to have the license information in the META files.

There are of course other required elements of the licensing. This article only focuses on the entry in the META files.