CPAN::Meta::Spec(3) User Contributed Perl Documentation CPAN::Meta::Spec(3)
NAME
CPAN::Meta::Spec - specification for CPAN distribution metadata
VERSION
version 2.150010
SYNOPSIS
my $distmeta = {
name => 'Module-Build',
abstract => 'Build and install Perl modules',
description => "Module::Build is a system for "
. "building, testing, and installing Perl modules. "
. "It is meant to ... blah blah blah ...",
version => '0.36',
release_status => 'stable',
author => [
'Ken Williams <kwilliams AT cpan.org>',
'Module-Build List <module-build AT perl.org>', # additional contact
],
license => [ 'perl_5' ],
prereqs => {
runtime => {
requires => {
'perl' => '5.006',
'ExtUtils::Install' => '0',
'File::Basename' => '0',
'File::Compare' => '0',
'IO::File' => '0',
},
recommends => {
'Archive::Tar' => '1.00',
'ExtUtils::Install' => '0.3',
'ExtUtils::ParseXS' => '2.02',
},
},
build => {
requires => {
'Test::More' => '0',
},
}
},
resources => {
license => ['http://dev.perl.org/licenses/'],
},
optional_features => {
domination => {
description => 'Take over the world',
prereqs => {
develop => { requires => { 'Genius::Evil' => '1.234' } },
runtime => { requires => { 'Machine::Weather' => '2.0' } },
},
},
},
dynamic_config => 1,
keywords => [ qw/ toolchain cpan dual-life / ],
'meta-spec' => {
version => '2',
url => 'https://metacpan.org/pod/CPAN::Meta::Spec',
},
generated_by => 'Module::Build version 0.36',
};
DESCRIPTION
This document describes version 2 of the CPAN distribution metadata
specification, also known as the "CPAN Meta Spec".
Revisions of this specification for typo corrections and prose
clarifications may be issued as CPAN::Meta::Spec 2.x. These revisions
will never change semantics or add or remove specified behavior.
Distribution metadata describe important properties of Perl
distributions. Distribution building tools like Module::Build,
Module::Install, ExtUtils::MakeMaker or Dist::Zilla should create a
metadata file in accordance with this specification and include it with
the distribution for use by automated tools that index, examine,
package or install Perl distributions.
TERMINOLOGY
distribution
This is the primary object described by the metadata. In the
context of this document it usually refers to a collection of
modules, scripts, and/or documents that are distributed together
for other developers to use. Examples of distributions are
"Class-Container", "libwww-perl", or "DBI".
module
This refers to a reusable library of code contained in a single
file. Modules usually contain one or more packages and are often
referred to by the name of a primary package that can be mapped to
the file name. For example, one might refer to "File::Spec" instead
of File/Spec.pm
package
This refers to a namespace declared with the Perl "package"
statement. In Perl, packages often have a version number property
given by the $VERSION variable in the namespace.
consumer
This refers to code that reads a metadata file, deserializes it
into a data structure in memory, or interprets a data structure of
metadata elements.
producer
This refers to code that constructs a metadata data structure,
serializes into a bytestream and/or writes it to disk.
must, should, may, etc.
These terms are interpreted as described in IETF RFC 2119.
DATA TYPES
Fields in the "STRUCTURE" section describe data elements, each of which
has an associated data type as described herein. There are four
primitive types: Boolean, String, List and Map. Other types are
subtypes of primitives and define compound data structures or define
constraints on the values of a data element.
Boolean
A Boolean is used to provide a true or false value. It must be
represented as a defined value that is either "1" or "0" or stringifies
to those values.
String
A String is data element containing a non-zero length sequence of
Unicode characters, such as an ordinary Perl scalar that is not a
reference.
List
A List is an ordered collection of zero or more data elements.
Elements of a List may be of mixed types.
Producers must represent List elements using a data structure which
unambiguously indicates that multiple values are possible, such as a
reference to a Perl array (an "arrayref").
Consumers expecting a List must consider a String as equivalent to a
List of length 1.
Map
A Map is an unordered collection of zero or more data elements
("values"), indexed by associated String elements ("keys"). The Map's
value elements may be of mixed types.
License String
A License String is a subtype of String with a restricted set of
values. Valid values are described in detail in the description of the
"license" field.
URL
URL is a subtype of String containing a Uniform Resource Locator or
Identifier. [ This type is called URL and not URI for historical
reasons. ]
Version
A Version is a subtype of String containing a value that describes the
version number of packages or distributions. Restrictions on format
are described in detail in the "Version Formats" section.
Version Range
The Version Range type is a subtype of String. It describes a range of
Versions that may be present or installed to fulfill prerequisites. It
is specified in detail in the "Version Ranges" section.
STRUCTURE
The metadata structure is a data element of type Map. This section
describes valid keys within the Map.
Any keys not described in this specification document (whether top-
level or within compound data structures described herein) are
considered custom keys and must begin with an "x" or "X" and be
followed by an underscore; i.e. they must match the pattern:
"qr{\Ax_}i". If a custom key refers to a compound data structure,
subkeys within it do not need an "x_" or "X_" prefix.
Consumers of metadata may ignore any or all custom keys. All other
keys not described herein are invalid and should be ignored by
consumers. Producers must not generate or output invalid keys.
For each key, an example is provided followed by a description. The
description begins with the version of spec in which the key was added
or in which the definition was modified, whether the key is required or
optional and the data type of the corresponding data element. These
items are in parentheses, brackets and braces, respectively.
If a data type is a Map or Map subtype, valid subkeys will be described
as well.
Some fields are marked Deprecated. These are shown for historical
context and must not be produced in or consumed from any metadata
structure of version 2 or higher.
REQUIRED FIELDS
abstract
Example:
abstract => 'Build and install Perl modules'
(Spec 1.2) [required] {String}
This is a short description of the purpose of the distribution.
author
Example:
author => [ 'Ken Williams <kwilliams AT cpan.org>' ]
(Spec 1.2) [required] {List of one or more Strings}
This List indicates the person(s) to contact concerning the
distribution. The preferred form of the contact string is:
contact-name <email-address>
This field provides a general contact list independent of other
structured fields provided within the "resources" field, such as
"bugtracker". The addressee(s) can be contacted for any purpose
including but not limited to (security) problems with the distribution,
questions about the distribution or bugs in the distribution.
A distribution's original author is usually the contact listed within
this field. Co-maintainers, successor maintainers or mailing lists
devoted to the distribution may also be listed in addition to or
instead of the original author.
dynamic_config
Example:
dynamic_config => 1
(Spec 2) [required] {Boolean}
A boolean flag indicating whether a Build.PL or Makefile.PL (or
similar) must be executed to determine prerequisites.
This field should be set to a true value if the distribution performs
some dynamic configuration (asking questions, sensing the environment,
etc.) as part of its configuration. This field should be set to a
false value to indicate that prerequisites included in metadata may be
considered final and valid for static analysis.
Note: when this field is true, post-configuration prerequisites are not
guaranteed to bear any relation whatsoever to those stated in the
metadata, and relying on them doing so is an error. See also
"Prerequisites for dynamically configured distributions" in the
implementors' notes.
This field explicitly does not indicate whether installation may be
safely performed without using a Makefile or Build file, as there may
be special files to install or custom installation targets (e.g. for
dual-life modules that exist on CPAN as well as in the Perl core).
This field only defines whether or not prerequisites are exactly as
given in the metadata.
generated_by
Example:
generated_by => 'Module::Build version 0.36'
(Spec 1.0) [required] {String}
This field indicates the tool that was used to create this metadata.
There are no defined semantics for this field, but it is traditional to
use a string in the form "Generating::Package version 1.23" or the
author's name, if the file was generated by hand.
license
Example:
license => [ 'perl_5' ]
license => [ 'apache_2_0', 'mozilla_1_0' ]
(Spec 2) [required] {List of one or more License Strings}
One or more licenses that apply to some or all of the files in the
distribution. If multiple licenses are listed, the distribution
documentation should be consulted to clarify the interpretation of
multiple licenses.
The following list of license strings are valid:
string description
------------- -----------------------------------------------
agpl_3 GNU Affero General Public License, Version 3
apache_1_1 Apache Software License, Version 1.1
apache_2_0 Apache License, Version 2.0
artistic_1 Artistic License, (Version 1)
artistic_2 Artistic License, Version 2.0
bsd BSD License (three-clause)
freebsd FreeBSD License (two-clause)
gfdl_1_2 GNU Free Documentation License, Version 1.2
gfdl_1_3 GNU Free Documentation License, Version 1.3
gpl_1 GNU General Public License, Version 1
gpl_2 GNU General Public License, Version 2
gpl_3 GNU General Public License, Version 3
lgpl_2_1 GNU Lesser General Public License, Version 2.1
lgpl_3_0 GNU Lesser General Public License, Version 3.0
mit MIT (aka X11) License
mozilla_1_0 Mozilla Public License, Version 1.0
mozilla_1_1 Mozilla Public License, Version 1.1
openssl OpenSSL License
perl_5 The Perl 5 License (Artistic 1 & GPL 1 or later)
qpl_1_0 Q Public License, Version 1.0
ssleay Original SSLeay License
sun Sun Internet Standards Source License (SISSL)
zlib zlib License
The following license strings are also valid and indicate other
licensing not described above:
string description
------------- -----------------------------------------------
open_source Other Open Source Initiative (OSI) approved license
restricted Requires special permission from copyright holder
unrestricted Not an OSI approved license, but not restricted
unknown License not provided in metadata
All other strings are invalid in the license field.
meta-spec
Example:
'meta-spec' => {
version => '2',
url => 'http://search.cpan.org/perldoc?CPAN::Meta::Spec',
}
(Spec 1.2) [required] {Map}
This field indicates the version of the CPAN Meta Spec that should be
used to interpret the metadata. Consumers must check this key as soon
as possible and abort further metadata processing if the meta-spec
version is not supported by the consumer.
The following keys are valid, but only "version" is required.
version
This subkey gives the integer Version of the CPAN Meta Spec against
which the document was generated.
url This is a URL of the metadata specification document corresponding
to the given version. This is strictly for human-consumption and
should not impact the interpretation of the document.
For the version 2 spec, either of these are recommended:
o "https://metacpan.org/pod/CPAN::Meta::Spec"
o "http://search.cpan.org/perldoc?CPAN::Meta::Spec"
name
Example:
name => 'Module-Build'
(Spec 1.0) [required] {String}
This field is the name of the distribution. This is often created by
taking the "main package" in the distribution and changing "::" to "-",
but the name may be completely unrelated to the packages within the
distribution. For example, LWP::UserAgent is distributed as part of
the distribution name "libwww-perl".
release_status
Example:
release_status => 'stable'
(Spec 2) [required] {String}
This field provides the release status of this distribution. If the
"version" field contains an underscore character, then "release_status"
must not be "stable."
The "release_status" field must have one of the following values:
stable
This indicates an ordinary, "final" release that should be indexed
by PAUSE or other indexers.
testing
This indicates a "beta" release that is substantially complete, but
has an elevated risk of bugs and requires additional testing. The
distribution should not be installed over a stable release without
an explicit request or other confirmation from a user. This
release status may also be used for "release candidate" versions of
a distribution.
unstable
This indicates an "alpha" release that is under active development,
but has been released for early feedback or testing and may be
missing features or may have serious bugs. The distribution should
not be installed over a stable release without an explicit request
or other confirmation from a user.
Consumers may use this field to determine how to index the distribution
for CPAN or other repositories in addition to or in replacement of
heuristics based on version number or file name.
version
Example:
version => '0.36'
(Spec 1.0) [required] {Version}
This field gives the version of the distribution to which the metadata
structure refers.
OPTIONAL FIELDS
description
Example:
description => "Module::Build is a system for "
. "building, testing, and installing Perl modules. "
. "It is meant to ... blah blah blah ...",
(Spec 2) [optional] {String}
A longer, more complete description of the purpose or intended use of
the distribution than the one provided by the "abstract" key.
keywords
Example:
keywords => [ qw/ toolchain cpan dual-life / ]
(Spec 1.1) [optional] {List of zero or more Strings}
A List of keywords that describe this distribution. Keywords must not
include whitespace.
no_index
Example:
no_index => {
file => [ 'My/Module.pm' ],
directory => [ 'My/Private' ],
package => [ 'My::Module::Secret' ],
namespace => [ 'My::Module::Sample' ],
}
(Spec 1.2) [optional] {Map}
This Map describes any files, directories, packages, and namespaces
that are private to the packaging or implementation of the distribution
and should be ignored by indexing or search tools. Note that this is a
list of exclusions, and the spec does not define what to include - see
"Indexing distributions a la PAUSE" in the implementors notes for more
information.
Valid subkeys are as follows:
file
A List of relative paths to files. Paths must be specified with
unix conventions.
directory
A List of relative paths to directories. Paths must be specified
with unix conventions.
[ Note: previous editions of the spec had "dir" instead of
"directory" ]
package
A List of package names.
namespace
A List of package namespaces, where anything below the namespace
must be ignored, but not the namespace itself.
In the example above for "no_index", "My::Module::Sample::Foo"
would be ignored, but "My::Module::Sample" would not.
optional_features
Example:
optional_features => {
sqlite => {
description => 'Provides SQLite support',
prereqs => {
runtime => {
requires => {
'DBD::SQLite' => '1.25'
}
}
}
}
}
(Spec 2) [optional] {Map}
This Map describes optional features with incremental prerequisites.
Each key of the "optional_features" Map is a String used to identify
the feature and each value is a Map with additional information about
the feature. Valid subkeys include:
description
This is a String describing the feature. Every optional feature
should provide a description
prereqs
This entry is required and has the same structure as that of the
"prereqs" key. It provides a list of package requirements that
must be satisfied for the feature to be supported or enabled.
There is one crucial restriction: the prereqs of an optional
feature must not include "configure" phase prereqs.
Consumers must not include optional features as prerequisites without
explicit instruction from users (whether via interactive prompting, a
function parameter or a configuration value, etc. ).
If an optional feature is used by a consumer to add additional
prerequisites, the consumer should merge the optional feature
prerequisites into those given by the "prereqs" key using the same
semantics. See "Merging and Resolving Prerequisites" for details on
merging prerequisites.
Suggestion for disuse: Because there is currently no way for a
distribution to specify a dependency on an optional feature of another
dependency, the use of "optional_feature" is discouraged. Instead,
create a separate, installable distribution that ensures the desired
feature is available. For example, if "Foo::Bar" has a "Baz" feature,
release a separate "Foo-Bar-Baz" distribution that satisfies
requirements for the feature.
prereqs
Example:
prereqs => {
runtime => {
requires => {
'perl' => '5.006',
'File::Spec' => '0.86',
'JSON' => '2.16',
},
recommends => {
'JSON::XS' => '2.26',
},
suggests => {
'Archive::Tar' => '0',
},
},
build => {
requires => {
'Alien::SDL' => '1.00',
},
},
test => {
recommends => {
'Test::Deep' => '0.10',
},
}
}
(Spec 2) [optional] {Map}
This is a Map that describes all the prerequisites of the distribution.
The keys are phases of activity, such as "configure", "build", "test"
or "runtime". Values are Maps in which the keys name the type of
prerequisite relationship such as "requires", "recommends", or
"suggests" and the value provides a set of prerequisite relations. The
set of relations must be specified as a Map of package names to version
ranges.
The full definition for this field is given in the "Prereq Spec"
section.
provides
Example:
provides => {
'Foo::Bar' => {
file => 'lib/Foo/Bar.pm',
version => '0.27_02',
},
'Foo::Bar::Blah' => {
file => 'lib/Foo/Bar/Blah.pm',
},
'Foo::Bar::Baz' => {
file => 'lib/Foo/Bar/Baz.pm',
version => '0.3',
},
}
(Spec 1.2) [optional] {Map}
This describes all packages provided by this distribution. This
information is used by distribution and automation mechanisms like
PAUSE, CPAN, metacpan.org and search.cpan.org to build indexes saying
in which distribution various packages can be found.
The keys of "provides" are package names that can be found within the
distribution. If a package name key is provided, it must have a Map
with the following valid subkeys:
file
This field is required. It must contain a Unix-style relative file
path from the root of the distribution directory to a file that
contains or generates the package. It may be given as "META.yml"
or "META.json" to claim a package for indexing without needing a
"*.pm".
version
If it exists, this field must contains a Version String for the
package. If the package does not have a $VERSION, this field must
be omitted.
resources
Example:
resources => {
license => [ 'http://dev.perl.org/licenses/' ],
homepage => 'http://sourceforge.net/projects/module-build',
bugtracker => {
web => 'http://rt.cpan.org/Public/Dist/Display.html?Name=CPAN-Meta',
mailto => 'meta-bugs AT example.com',
},
repository => {
url => 'git://github.com/dagolden/cpan-meta.git',
web => 'http://github.com/dagolden/cpan-meta',
type => 'git',
},
x_twitter => 'http://twitter.com/cpan_linked/',
}
(Spec 2) [optional] {Map}
This field describes resources related to this distribution.
Valid subkeys include:
homepage
The official home of this project on the web.
license
A List of URL's that relate to this distribution's license. As
with the top-level "license" field, distribution documentation
should be consulted to clarify the interpretation of multiple
licenses provided here.
bugtracker
This entry describes the bug tracking system for this distribution.
It is a Map with the following valid keys:
web - a URL pointing to a web front-end for the bug tracker
mailto - an email address to which bugs can be sent
repository
This entry describes the source control repository for this
distribution. It is a Map with the following valid keys:
url - a URL pointing to the repository itself
web - a URL pointing to a web front-end for the repository
type - a lowercase string indicating the VCS used
Because a url like "http://myrepo.example.com/" is ambiguous as to
type, producers should provide a "type" whenever a "url" key is
given. The "type" field should be the name of the most common
program used to work with the repository, e.g. "git", "svn", "cvs",
"darcs", "bzr" or "hg".
DEPRECATED FIELDS
build_requires
(Deprecated in Spec 2) [optional] {String}
Replaced by "prereqs"
configure_requires
(Deprecated in Spec 2) [optional] {String}
Replaced by "prereqs"
conflicts
(Deprecated in Spec 2) [optional] {String}
Replaced by "prereqs"
distribution_type
(Deprecated in Spec 2) [optional] {String}
This field indicated 'module' or 'script' but was considered
meaningless, since many distributions are hybrids of several kinds of
things.
license_uri
(Deprecated in Spec 1.2) [optional] {URL}
Replaced by "license" in "resources"
private
(Deprecated in Spec 1.2) [optional] {Map}
This field has been renamed to "no_index".
recommends
(Deprecated in Spec 2) [optional] {String}
Replaced by "prereqs"
requires
(Deprecated in Spec 2) [optional] {String}
Replaced by "prereqs"
VERSION NUMBERS
Version Formats
This section defines the Version type, used by several fields in the
CPAN Meta Spec.
Version numbers must be treated as strings, not numbers. For example,
1.200 must not be serialized as 1.2. Version comparison should be
delegated to the Perl version module, version 0.80 or newer.
Unless otherwise specified, version numbers must appear in one of two
formats:
Decimal versions
Decimal versions are regular "decimal numbers", with some
limitations. They must be non-negative and must begin and end with
a digit. A single underscore may be included, but must be between
two digits. They must not use exponential notation ("1.23e-2").
version => '1.234' # OK
version => '1.23_04' # OK
version => '1.23_04_05' # Illegal
version => '1.' # Illegal
version => '.1' # Illegal
Dotted-integer versions
Dotted-integer (also known as dotted-decimal) versions consist of
positive integers separated by full stop characters (i.e. "dots",
"periods" or "decimal points"). This are equivalent in format to
Perl "v-strings", with some additional restrictions on form. They
must be given in "normal" form, which has a leading "v" character
and at least three integer components. To retain a one-to-one
mapping with decimal versions, all components after the first
should be restricted to the range 0 to 999. The final component
may be separated by an underscore character instead of a period.
version => 'v1.2.3' # OK
version => 'v1.2_3' # OK
version => 'v1.2.3.4' # OK
version => 'v1.2.3_4' # OK
version => 'v2009.10.31' # OK
version => 'v1.2' # Illegal
version => '1.2.3' # Illegal
version => 'v1.2_3_4' # Illegal
version => 'v1.2009.10.31' # Not recommended
Version Ranges
Some fields (prereq, optional_features) indicate the particular
version(s) of some other module that may be required as a prerequisite.
This section details the Version Range type used to provide this
information.
The simplest format for a Version Range is just the version number
itself, e.g. 2.4. This means that at least version 2.4 must be
present. To indicate that any version of a prerequisite is okay, even
if the prerequisite doesn't define a version at all, use the version 0.
Alternatively, a version range may use the operators < (less than), <=
(less than or equal), > (greater than), >= (greater than or equal), ==
(equal), and != (not equal). For example, the specification "< 2.0"
means that any version of the prerequisite less than 2.0 is suitable.
For more complicated situations, version specifications may be AND-ed
together using commas. The specification ">= 1.2, != 1.5, < 2.0"
indicates a version that must be at least 1.2, less than 2.0, and not
equal to 1.5.
PREREQUISITES
Prereq Spec
The "prereqs" key in the top-level metadata and within
"optional_features" define the relationship between a distribution and
other packages. The prereq spec structure is a hierarchical data
structure which divides prerequisites into Phases of activity in the
installation process and Relationships that indicate how prerequisites
should be resolved.
For example, to specify that "Data::Dumper" is "required" during the
"test" phase, this entry would appear in the distribution metadata:
prereqs => {
test => {
requires => {
'Data::Dumper' => '2.00'
}
}
}
Phases
Requirements for regular use must be listed in the "runtime" phase.
Other requirements should be listed in the earliest stage in which they
are required and consumers must accumulate and satisfy requirements
across phases before executing the activity. For example, "build"
requirements must also be available during the "test" phase.
before action requirements that must be met
---------------- --------------------------------
perl Build.PL configure
perl Makefile.PL
make configure, runtime, build
Build
make test configure, runtime, build, test
Build test
Consumers that install the distribution must ensure that runtime
requirements are also installed and may install dependencies from other
phases.
after action requirements that must be met
---------------- --------------------------------
make install runtime
Build install
configure
The configure phase occurs before any dynamic configuration has
been attempted. Libraries required by the configure phase must be
available for use before the distribution building tool has been
executed.
build
The build phase is when the distribution's source code is compiled
(if necessary) and otherwise made ready for installation.
test
The test phase is when the distribution's automated test suite is
run. Any library that is needed only for testing and not for
subsequent use should be listed here.
runtime
The runtime phase refers not only to when the distribution's
contents are installed, but also to its continued use. Any library
that is a prerequisite for regular use of this distribution should
be indicated here.
develop
The develop phase's prereqs are libraries needed to work on the
distribution's source code as its author does. These tools might
be needed to build a release tarball, to run author-only tests, or
to perform other tasks related to developing new versions of the
distribution.
Relationships
requires
These dependencies must be installed for proper completion of the
phase.
recommends
Recommended dependencies are strongly encouraged and should be
satisfied except in resource constrained environments.
suggests
These dependencies are optional, but are suggested for enhanced
operation of the described distribution.
conflicts
These libraries cannot be installed when the phase is in operation.
This is a very rare situation, and the "conflicts" relationship
should be used with great caution, or not at all.
Merging and Resolving Prerequisites
Whenever metadata consumers merge prerequisites, either from different
phases or from "optional_features", they should merged in a way which
preserves the intended semantics of the prerequisite structure.
Generally, this means concatenating the version specifications using
commas, as described in the "Version Ranges" section.
Another subtle error that can occur in resolving prerequisites comes
from the way that modules in prerequisites are indexed to distribution
files on CPAN. When a module is deleted from a distribution,
prerequisites calling for that module could indicate an older
distribution should be installed, potentially overwriting files from a
newer distribution.
For example, as of Oct 31, 2009, the CPAN index file contained these
module-distribution mappings:
Class::MOP 0.94 D/DR/DROLSKY/Class-MOP-0.94.tar.gz
Class::MOP::Class 0.94 D/DR/DROLSKY/Class-MOP-0.94.tar.gz
Class::MOP::Class::Immutable 0.04 S/ST/STEVAN/Class-MOP-0.36.tar.gz
Consider the case where "Class::MOP" 0.94 is installed. If a
distribution specified "Class::MOP::Class::Immutable" as a
prerequisite, it could result in Class-MOP-0.36.tar.gz being installed,
overwriting any files from Class-MOP-0.94.tar.gz.
Consumers of metadata should test whether prerequisites would result in
installed module files being "downgraded" to an older version and may
warn users or ignore the prerequisite that would cause such a result.
SERIALIZATION
Distribution metadata should be serialized (as a hashref) as JSON-
encoded data and packaged with distributions as the file META.json.
In the past, the distribution metadata structure had been packed with
distributions as META.yml, a file in the YAML Tiny format (for which,
see YAML::Tiny). Tools that consume distribution metadata from disk
should be capable of loading META.yml, but should prefer META.json if
both are found.
NOTES FOR IMPLEMENTORS
Extracting Version Numbers from Perl Modules
To get the version number from a Perl module, consumers should use the
"MM->parse_version($file)" method provided by ExtUtils::MakeMaker or
Module::Metadata. For example, for the module given by $mod, the
version may be retrieved in one of the following ways:
# via ExtUtils::MakeMaker
my $file = MM->_installed_file_for_module($mod);
my $version = MM->parse_version($file)
The private "_installed_file_for_module" method may be replaced with
other methods for locating a module in @INC.
# via Module::Metadata
my $info = Module::Metadata->new_from_module($mod);
my $version = $info->version;
If only a filename is available, the following approach may be used:
# via Module::Build
my $info = Module::Metadata->new_from_file($file);
my $version = $info->version;
Comparing Version Numbers
The version module provides the most reliable way to compare version
numbers in all the various ways they might be provided or might exist
within modules. Given two strings containing version numbers, $v1 and
$v2, they should be converted to "version" objects before using
ordinary comparison operators. For example:
use version;
if ( version->new($v1) <=> version->new($v2) ) {
print "Versions are not equal\n";
}
If the only comparison needed is whether an installed module is of a
sufficiently high version, a direct test may be done using the string
form of "eval" and the "use" function. For example, for module $mod
and version prerequisite $prereq:
if ( eval "use $mod $prereq (); 1" ) {
print "Module $mod version is OK.\n";
}
If the values of $mod and $prereq have not been scrubbed, however, this
presents security implications.
Prerequisites for dynamically configured distributions
When "dynamic_config" is true, it is an error to presume that the
prerequisites given in distribution metadata will have any relationship
whatsoever to the actual prerequisites of the distribution.
In practice, however, one can generally expect such prerequisites to be
one of two things:
o The minimum prerequisites for the distribution, to which dynamic
configuration will only add items
o Whatever the distribution configured with on the releaser's machine
at release time
The second case often turns out to have identical results to the first
case, albeit only by accident.
As such, consumers may use this data for informational analysis, but
presenting it to the user as canonical or relying on it as such is
invariably the height of folly.
Indexing distributions a la PAUSE
While no_index tells you what must be ignored when indexing, this spec
holds no opinion on how you should get your initial candidate list of
things to possibly index. For "normal" distributions you might consider
simply indexing the contents of lib/, but there are many fascinating
oddities on CPAN and many dists from the days when it was normal to put
the main .pm file in the root of the distribution archive - so PAUSE
currently indexes all .pm and .PL files that are not either (a)
specifically excluded by no_index (b) in "inc", "xt", or "t"
directories, or common 'mistake' directories such as "perl5".
Or: If you're trying to be PAUSE-like, make sure you skip "inc", "xt"
and "t" as well as anything marked as no_index.
Also remember: If the META file contains a provides field, you
shouldn't be indexing anything in the first place - just use that.
SEE ALSO
o CPAN, <http://www.cpan.org/>;
o JSON, <http://json.org/>;
o YAML, <http://www.yaml.org/>;
o CPAN
o CPANPLUS
o ExtUtils::MakeMaker
o Module::Build
o Module::Install
o CPAN::Meta::History::Meta_1_4
HISTORY
Ken Williams wrote the original CPAN Meta Spec (also known as the
"META.yml spec") in 2003 and maintained it through several revisions
with input from various members of the community. In 2005, Randy Sims
redrafted it from HTML to POD for the version 1.2 release. Ken
continued to maintain the spec through version 1.4.
In late 2009, David Golden organized the version 2 proposal review
process. David and Ricardo Signes drafted the final version 2 spec in
April 2010 based on the version 1.4 spec and patches contributed during
the proposal process.
AUTHORS
o David Golden <dagolden AT cpan.org>
o Ricardo Signes <rjbs AT cpan.org>
o Adam Kennedy <adamk AT cpan.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2010 by David Golden, Ricardo Signes,
Adam Kennedy and Contributors.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
perl v5.26.3 2016-08-18 CPAN::Meta::Spec(3)
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