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 <title>Specification for META.yml</title>
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<h2 align=center>Specification for the META.yml file</h2>

<p>This document describes version 1.0 of the META.yml specification.</p>

<p>
The META.yml file describes important properties of contributed Perl
distributions such as the ones found on <a
href="http://www.cpan.org">CPAN</a>.  It is typically created by tools
like <a
href="http://search.cpan.org/author/KWILLIAMS/Module-Build/">Module::Build</a>
and <a
href="http://search.cpan.org/author/MSCHWERN/ExtUtils-MakeMaker/">ExtUtils::MakeMaker</a>.
</p>

<p>
The fields in the META.yml file are meant to be helpful to people
maintaining module collections (like CPAN), for people writing
installation tools (like <a
href="http://search.cpan.org/author/ANDK/CPAN/">CPAN.pm</a> or <a
href="http://search.cpan.org/author/KANE/CPANPLUS/">CPANPLUS</a>), or
just people who want to know some stuff about a distribution before
downloading it and starting to install it.
</p>

<h3>Format</h3>

<p>
META.yml files are written in the <a
href="http://www.yaml.org/">YAML</a> format.  The reasons we chose
YAML instead of, say, XML or Data::Dumper are discussed in <a
href="http://archive.develooper.com/makemaker@perl.org/msg00405.html">this
thread</a> on the MakeMaker mailing list.
</p>

<p>
The first line of a META.yml file should be a valid <a
href="http://www.yaml.org/spec/#.Document">YAML document header</a>
like <nobr><tt>"--- #YAML:1.0"</tt></nobr>.
</p>

<h3>Fields</h3>

<p>
The rest of the META.yml file is one big YAML <a
href="http://www.yaml.org/spec/#.-syntax-mapping-Mapping-">mapping</a>,
whose keys are described here.
</p>

<ul>

<li><b>name</b><br>
Example: <b>Module-Build</b>
<p>
The name of the distribution.  Often created by taking the "main
module" in the distribution and changing "::" to "-".  Sometimes it's
completely different, however, as in the case of the <a
href="http://search.cpan.org/author/GAAS/libwww-perl/">libwww-perl</a>
distribution.
</p>

<li><b>version</b><br>
Example: <b>0.16</b>
<p>
The version of the distribution to which the META.yml file refers.
</p>

<li><b>license</b><br>
Example: <b>perl</b>
<p>
The license under which this distribution may be used and
redistributed.  See <a
href="http://search.cpan.org/author/KWILLIAMS/Module-Build/">Module::Build</a>
for the list of valid options.
</p>

<li><b>distribution_type</b><br>
Example: <b>module</b>
<p>
What kind of stuff is contained in this distribution.  Most things on
CPAN are <code>module</code>s (which can also mean a collection of
modules), but some things are <code>script</code>s.
</p>

<li><b>requires</b><br>
Example:<br>
<b>
&nbsp;&nbsp;Data::Dumper: 0<br>
&nbsp;&nbsp;File::Find: 1.03<br>
</b>   
<p>
A YAML <a
href="http://www.yaml.org/spec/#.-syntax-mapping-Mapping-">mapping</a>
indicating the Perl modules this distribution requires for proper
operation.  The keys are the module names, and the values are version
specifications as described in the <a
href="http://search.cpan.org/author/KWILLIAMS/Module-Build/lib/Module/Build.pm">
documentation for Module::Build's "requires" parameter</a>.
</p>

<p><i>Note: the exact nature of the fancy specifications like
<nobr><tt>"&gt;= 1.2, != 1.5, &lt 2.0"</tt></nobr> is subject to
change.  Advance notice will be given here.  The simple specifications
like <tt>"1.2"</tt> will not change in format.</i>
</p>

<li><b>recommends</b><br>
Example:<br>
<b>
&nbsp;&nbsp;Data::Dumper: 0<br>
&nbsp;&nbsp;File::Find: 1.03<br>
</b>   
<p>
A YAML <a
href="http://www.yaml.org/spec/#.-syntax-mapping-Mapping-">mapping</a>
indicating the Perl modules this distribution recommends for enhanced
operation.
</p>

<li><b>build_requires</b><br>
Example:<br>
<b>
&nbsp;&nbsp;Data::Dumper: 0<br>
&nbsp;&nbsp;File::Find: 1.03<br>
</b>   
<p>
A YAML <a
href="http://www.yaml.org/spec/#.-syntax-mapping-Mapping-">mapping</a>
indicating the Perl modules required for building and/or testing of
this distribution.  These dependencies are not required after the
module is installed.
</p>

<li><b>conflicts</b><br>
Example:<br>
<b>
&nbsp;&nbsp;Data::Dumper: 0<br>
&nbsp;&nbsp;File::Find: 1.03<br>
</b>   
<p>
A YAML <a
href="http://www.yaml.org/spec/#.-syntax-mapping-Mapping-">mapping</a>
indicating the Perl modules that cannot be installed while this
distribution is installed.  This is a pretty uncommon situation.
</p>

<li><b>dynamic_config</b><br>
Example: <b>0</b>
<p>
A boolean flag indicating whether a <tt>Build.PL</tt> or
<tt>Makefile.PL</tt> (or similar) must be executed, or whether this
module can be built, tested and installed solely from consulting its
metadata file.  The main reason to set this to a true value if that
your module performs some dynamic configuration (asking questions,
sensing the environment, etc.) as part of its build/install process.
</p>

<p>
Currently <tt>Module::Build</tt> doesn't actually do anything with
this flag - it's probably going to be up to higher-level tools like
<tt>CPAN.pm</tt> to do something useful with it.  It can potentially
bring lots of security, packaging, and convenience improvements.
</p>

<li><b>generated_by</b><br>
Example: <b>Module::Build version 0.16</b>
<p>
Indicates the tool that was used to create this META.yml file.  It's
good form to include both the name of the tool and its version, but
this field is essentially opaque, at least for the moment.
</p>

</ul>

<h3>Related Projects</h3>
<dl>
 <dt>DOAP</dt>

 <dd>An RDF vocabulary to describe software projects. <a
 href="http://usefulinc.com/doap">http://usefulinc.com/doap</a>.</dd>
</dl>

<h3>History</h3>

<ul>
<li><b>March 14, 2003</b> (Pi day) - created version 1.0 of this document.</li>
<li><b>May 8, 2003</b> - added the "dynamic_config" field, which was
    missing from the initial version.</li> 
</ul>

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