NAME¶
CPAN::Meta::Spec - specification for CPAN distribution metadata
VERSION¶
version 2.142690
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@cpan.org>',
'Module-Build List <module-build@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.
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@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:
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@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¶
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¶
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.
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:
- •
- The minimum prerequisites for the distribution, to which dynamic
configuration will only add items
- •
- 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¶
- •
- CPAN, <http://www.cpan.org/>
- •
- JSON, <http://json.org/>
- •
- YAML, <http://www.yaml.org/>
- •
- CPAN
- •
- CPANPLUS
- •
- ExtUtils::MakeMaker
- •
- Module::Build
- •
- Module::Install
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¶
- •
- David Golden <dagolden@cpan.org>
- •
- Ricardo Signes <rjbs@cpan.org>
COPYRIGHT AND LICENSE¶
This software is copyright (c) 2010 by David Golden and Ricardo Signes.
This is free software; you can redistribute it and/or modify it under the same
terms as the Perl 5 programming language system itself.