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Ken Williams
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Module::Build::Authoring - Authoring Module::Build modules


When creating a Build.PL script for a module, something like the following code will typically be used:

  use Module::Build;
  my $build = Module::Build->new
     module_name => 'Foo::Bar',
     license  => 'perl',
     requires => {
                  'perl'          => '5.6.1',
                  'Some::Module'  => '1.23',
                  'Other::Module' => '>= 1.2, != 1.5, < 2.0',

A simple module could get away with something as short as this for its Build.PL script:

  use Module::Build;
    module_name => 'Foo::Bar',
    license     => 'perl',

The model used by Module::Build is a lot like the MakeMaker metaphor, with the following correspondences:

   In Module::Build                 In ExtUtils::MakeMaker
  ---------------------------      ------------------------
   Build.PL (initial script)        Makefile.PL (initial script)
   Build (a short perl script)      Makefile (a long Makefile)
   _build/ (saved state info)       various config text in the Makefile

Any customization can be done simply by subclassing Module::Build and adding a method called (for example) ACTION_test, overriding the default 'test' action. You could also add a method called ACTION_whatever, and then you could perform the action Build whatever.

For information on providing compatibility with ExtUtils::MakeMaker, see Module::Build::Compat and http://www.makemaker.org/wiki/index.cgi?ModuleBuildConversionGuide.


I list here some of the most important methods in Module::Build. Normally you won't need to deal with these methods unless you want to subclass Module::Build. But since one of the reasons I created this module in the first place was so that subclassing is possible (and easy), I will certainly write more docs as the interface stabilizes.



This method returns a reasonable facsimile of the currently-executing Module::Build object representing the current build. You can use this object to query its notes() method, inquire about installed modules, and so on. This is a great way to share information between different parts of your build process. For instance, you can ask the user a question during perl Build.PL, then use their answer during a regression test:

  # In Build.PL:
  my $color = $build->prompt("What is your favorite color?");
  $build->notes(color => $color);

  # In t/colortest.t:
  use Module::Build;
  my $build = Module::Build->current;
  my $color = $build->notes('color');

The way the current() method is currently implemented, there may be slight differences between the $build object in Build.PL and the one in t/colortest.t. It is our goal to minimize these differences in future releases of Module::Build, so please report any anomalies you find.

One important caveat: in its current implementation, current() will NOT work correctly if you have changed out of the directory that Module::Build was invoked from.


Creates a new Module::Build object. Arguments to the new() method are listed below. Most arguments are optional, but you must provide either the module_name argument, or dist_name and one of dist_version or dist_version_from. In other words, you must provide enough information to determine both a distribution name and version.


An array reference of files to be cleaned up when the clean action is performed. See also the add_to_cleanup() method.


This parameter supports the setting of features (see feature($name)) automatically based on a set of prerequisites. For instance, for a module that could optionally use either MySQL or PostgreSQL databases, you might use auto_features like this:

  my $build = Module::Build->new
     ...other stuff here...
     auto_features => {
       pg_support    => {
                         description => "Interface with Postgres databases",
                         requires    => { 'DBD::Pg' => 23.3,
                                          'DateTime::Format::Pg' => 0 },
       mysql_support => {
                         description => "Interface with MySQL databases",
                         requires    => { 'DBD::mysql' => 17.9,
                                          'DateTime::Format::MySQL' => 0 },

For each feature named, the required prerequisites will be checked, and if there are no failures, the feature will be enabled (set to 1). Otherwise the failures will be displayed to the user and the feature will be disabled (set to 0).

See the documentation for requires for the details of how requirements can be specified.


An optional autosplit argument specifies a file which should be run through the Autosplit::autosplit() function. If multiple files should be split, the argument may be given as an array of the files to split.

In general I don't consider autosplitting a great idea, because it's not always clear that autosplitting achieves its intended performance benefits. It may even harm performance in environments like mod_perl, where as much as possible of a module's code should be loaded during startup.


The Module::Build class or subclass to use in the build script. Defaults to "Module::Build" or the class name passed to or created by a call to subclass(). This property is useful if you're writing a custom Module::Build subclass and have a bootstrapping problem--that is, your subclass requires modules that may not be installed when perl Build.PL is executed, but you've listed in build_requires so that they should be available when ./Build is executed.


Modules listed in this section are necessary to build and install the given module, but are not necessary for regular usage of it. This is actually an important distinction - it allows for tighter control over the body of installed modules, and facilitates correct dependency checking on binary/packaged distributions of the module.

See the documentation for "PREREQUISITES" for the details of how requirements can be specified.


An optional c_source argument specifies a directory which contains C source files that the rest of the build may depend on. Any .c files in the directory will be compiled to object files. The directory will be added to the search path during the compilation and linking phases of any C or XS files.


Modules listed in this section conflict in some serious way with the given module. Module::Build (or some higher-level tool) will refuse to install the given module if the given module/version is also installed.

See the documentation for "PREREQUISITES" for the details of how requirements can be specified.


This parameter lets you use Module::Build::Compat during the distdir (or dist) action to automatically create a Makefile.PL for compatibility with ExtUtils::MakeMaker. The parameter's value should be one of the styles named in the Module::Build::Compat documentation.


This parameter tells Module::Build to automatically create a README file at the top level of your distribution. Currently it will simply use Pod::Text (or Pod::Readme if it's installed) on the file indicated by dist_version_from and put the result in the README file. This is by no means the only recommended style for writing a README, but it seems to be one common one used on the CPAN.

If you generate a README in this way, it's probably a good idea to create a separate INSTALL file if that information isn't in the generated README.


This should be a short description of the distribution. This is used when generating metadata for META.yml and PPD files. If it is not given then Module::Build looks in the POD of the module from which it gets the distribution's version. It looks for the first line matching $package\s-\s(.+), and uses the captured text as the abstract.


This should be something like "John Doe <jdoe@example.com>", or if there are multiple authors, an anonymous array of strings may be specified. This is used when generating metadata for META.yml and PPD files. If this is not specified, then Module::Build looks at the module from which it gets the distribution's version. If it finds a POD section marked "=head1 AUTHOR", then it uses the contents of this section.


Specifies the name for this distribution. Most authors won't need to set this directly, they can use module_name to set dist_name to a reasonable default. However, some agglomerative distributions like libwww-perl or bioperl have names that don't correspond directly to a module name, so dist_name can be set independently.


Specifies a version number for the distribution. See module_name or dist_version_from for ways to have this set automatically from a $VERSION variable in a module. One way or another, a version number needs to be set.


Specifies a file to look for the distribution version in. Most authors won't need to set this directly, they can use module_name to set it to a reasonable default.

The version is extracted from the specified file according to the same rules as ExtUtils::MakeMaker and CPAN.pm. It involves finding the first line that matches the regular expression


eval()-ing that line, then checking the value of the $VERSION variable. Quite ugly, really, but all the modules on CPAN depend on this process, so there's no real opportunity to change to something better.


A boolean flag indicating whether the Build.PL file must be executed, or whether this module can be built, tested and installed solely from consulting its metadata file. The default value is 0, reflecting the fact that "most" of the modules on CPAN just need to be copied from one place to another. The main reason to set this to a true value is that your module performs some dynamic configuration as part of its build/install process.

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


These parameters can contain array references (or strings, in which case they will be split into arrays) to pass through to the compiler and linker phases when compiling/linking C code. For example, to tell the compiler that your code is C++, you might do:

  my $build = Module::Build->new
     module_name          => 'Foo::Bar',
     extra_compiler_flags => ['-x', 'c++'],

To link your XS code against glib you might write something like:

  my $build = Module::Build->new
     module_name          => 'Foo::Bar',
     dynamic_config       => 1,
     extra_compiler_flags => scalar `glib-config --cflags`,
     extra_linker_flags   => scalar `glib-config --libs`,

You can pass arbitrary command line options to Build.PL or Build, and they will be stored in the Module::Build object and can be accessed via the args() method. However, sometimes you want more flexibility out of your argument processing than this allows. In such cases, use the get_options parameter to pass in a hash reference of argument specifications, and the list of arguments to Build.PL or Build will be processed according to those specifications before they're passed on to Module::Build's own argument processing.

The supported option specification hash keys are:


The type of option. The types are those supported by Getopt::Long; consult its documentation for a complete list. Typical types are =s for strings, + for additive options, and ! for negatable options. If the type is not specified, it will be considered a boolean, i.e. no argument is taken and a value of 1 will be assigned when the option is encountered.


A reference to a scalar in which to store the value passed to the option. If not specified, the value will be stored under the option name in the hash returned by the args() method.


A default value for the option. If no default value is specified and no option is passed, then the option key will not exist in the hash returned by args().

You can combine references to your own variables or subroutines with unreferenced specifications, for which the result will also be stored in the hash returned by args(). For example:

  my $loud = 0;
  my $build = Module::Build->new
     module_name => 'Foo::Bar',
     get_options => {
                     loud =>     { store => \$loud },
                     dbd  =>     { type  => '=s'   },
                     quantity => { type  => '+'    },

  print STDERR "HEY, ARE YOU LISTENING??\n" if $loud;
  print "We'll use the ", $build->args('dbd'), " DBI driver\n";
  print "Are you sure you want that many?\n"
    if $build->args('quantity') > 2;

The arguments for such a specification can be called like so:

  perl Build.PL --loud --dbd=DBD::pg --quantity --quantity --quantity

WARNING: Any option specifications that conflict with Module::Build's own options (defined by its properties) will throw an exception.

Consult the Getopt::Long documentation for details on its usage.


Specifies any additional directories in which to search for C header files. May be given as a string indicating a single directory, or as a list reference indicating multiple directories.


You can set paths for individual installable elements by using the install_path parameter:

  my $build = Module::Build->new
     ...other stuff here...
     install_path => {
                      lib  => '/foo/lib',
                      arch => '/foo/lib/arch',

Determines where files are installed within the normal perl hierarchy as determined by Config.pm. Valid values are: core, site, vendor. The default is site. See "INSTALL PATHS" in Module::Build


Specifies the licensing terms of your distribution. Valid options include:


The distribution is licensed under the Apache Software License (http://opensource.org/licenses/apachepl.php).


The distribution is licensed under the Artistic License, as specified by the Artistic file in the standard perl distribution.


The distribution is licensed under the BSD License (http://www.opensource.org/licenses/bsd-license.php).


The distribution is licensed under the terms of the Gnu General Public License (http://www.opensource.org/licenses/gpl-license.php).


The distribution is licensed under the terms of the Gnu Lesser General Public License (http://www.opensource.org/licenses/lgpl-license.php).


The distribution is licensed under the MIT License (http://opensource.org/licenses/mit-license.php).


The distribution is licensed under the Mozilla Public License. (http://opensource.org/licenses/mozilla1.0.php or http://opensource.org/licenses/mozilla1.1.php)


The distribution is licensed under some other Open Source Initiative-approved license listed at http://www.opensource.org/licenses/ .


The distribution may be copied and redistributed under the same terms as perl itself (this is by far the most common licensing option for modules on CPAN). This is a dual license, in which the user may choose between either the GPL or the Artistic license.


The distribution may not be redistributed without special permission from the author and/or copyright holder.


The distribution is licensed under a license that is not approved by www.opensource.org but that allows distribution without restrictions.

Note that you must still include the terms of your license in your documentation - this field only lets automated tools figure out your licensing restrictions. Humans still need something to read. If you choose to provide this field, you should make sure that you keep it in sync with your written documentation if you ever change your licensing terms.

It is a fatal error to use a license other than the ones mentioned above. This is not because I wish to impose licensing terms on you - please let me know if you would like another license option to be added to the list. You may also use a license type of unknown if you don't wish to specify your terms (but this is usually not a good idea for you to do!).

I just started out with a small set of licenses to keep things simple, figuring I'd let people with actual working knowledge in this area tell me what to do. So if that's you, drop me a line.


A hash of key/value pairs that should be added to the META.yml file during the distmeta action. Any existing entries with the same names will be overridden.


A hash of key/value pairs that should be merged into the META.yml file during the distmeta action. Any existing entries with the same names will be overridden.

The only difference between meta_add and meta_merge is their behavior on hash-valued and array-valued entries: meta_add will completely blow away the existing hash or array value, but meta_merge will merge the supplied data into the existing hash or array value.


The module_name is a shortcut for setting default values of dist_name and dist_version_from, reflecting the fact that the majority of CPAN distributions are centered around one "main" module. For instance, if you set module_name to Foo::Bar, then dist_name will default to Foo-Bar and dist_version_from will default to lib/Foo/Bar.pm. dist_version_from will in turn be used to set dist_version.

Setting module_name won't override a dist_* parameter you specify explicitly.


An optional parameter specifying a set of .PL files in your distribution. These will be run as Perl scripts prior to processing the rest of the files in your distribution. They are usually used as templates for creating other files dynamically, so that a file like lib/Foo/Bar.pm.PL might create the file lib/Foo/Bar.pm.

The files are specified with the .PL files as hash keys, and the file(s) they generate as hash values, like so:

  my $build = Module::Build->new
     module_name => 'Foo::Bar',
     PL_files => { 'lib/Foo/Bar.pm.PL' => 'lib/Foo/Bar.pm' },

Note that the path specifications are always given in Unix-like format, not in the style of the local system.

If your .PL scripts don't create any files, or if they create files with unexpected names, or even if they create multiple files, you can indicate that so that Module::Build can properly handle these created files:

  PL_files => {
               'lib/Foo/Bar.pm.PL' => 'lib/Foo/Bar.pm',
               'lib/something.PL'  => ['/lib/something', '/lib/else'],
               'lib/funny.PL'      => [],

An optional parameter specifying the set of .pm files in this distribution, specified as a hash reference whose keys are the files' locations in the distributions, and whose values are their logical locations based on their package name, i.e. where they would be found in a "normal" Module::Build-style distribution. This parameter is mainly intended to support alternative layouts of files.

For instance, if you have an old-style MakeMaker distribution for a module called Foo::Bar and a Bar.pm file at the top level of the distribution, you could specify your layout in your Build.PL like this:

  my $build = Module::Build->new
     module_name => 'Foo::Bar',
     pm_files => { 'Bar.pm' => 'lib/Foo/Bar.pm' },

Note that the values should include lib/, because this is where they would be found in a "normal" Module::Build-style distribution.

Note also that the path specifications are always given in Unix-like format, not in the style of the local system.


Just like pm_files, but used for specifying the set of .pod files in your distribution.


This is just like the requires argument, except that modules listed in this section aren't essential, just a good idea. We'll just print a friendly warning if one of these modules aren't found, but we'll continue running.

If a module is recommended but not required, all tests should still pass if the module isn't installed. This may mean that some tests may be skipped if recommended dependencies aren't present.

Automated tools like CPAN.pm should inform the user when recommended modules aren't installed, and it should offer to install them if it wants to be helpful.

See the documentation for "PREREQUISITES" for the details of how requirements can be specified.


An optional requires argument specifies any module prerequisites that the current module depends on.

One note: currently Module::Build doesn't actually require the user to have dependencies installed, it just strongly urges. In the future we may require it. There's also a recommends section for things that aren't absolutely required.

Automated tools like CPAN.pm should refuse to install a module if one of its dependencies isn't satisfied, unless a "force" command is given by the user. If the tools are helpful, they should also offer to install the dependencies.

A synonym for requires is prereq, to help succour people transitioning from ExtUtils::MakeMaker. The requires term is preferred, but the prereq term will remain valid in future distributions.

See the documentation for "PREREQUISITES" for the details of how requirements can be specified.


An optional parameter specifying a set of files that should be installed as executable perl scripts when the module is installed. May be given as an array reference of the files, or as a hash reference whose keys are the files (and whose values will currently be ignored).

The default is to install no script files - in other words, there is no default location where Module::Build will look for script files to install.

For backward compatibility, you may use the parameter scripts instead of script_files. Please consider this usage deprecated, though it will continue to exist for several version releases.


If a true value is specified for this parameter, Module::Signature will be used (via the 'distsign' action) to create a SIGNATURE file for your distribution during the 'distdir' action, and to add the SIGNATURE file to the MANIFEST (therefore, don't add it yourself).

The default value is false. In the future, the default may change to true if you have Module::Signature installed on your system.


An optional parameter specifying a set of files that should be used as Test::Harness-style regression tests to be run during the test action. May be given as an array reference of the files, or as a hash reference whose keys are the files (and whose values will currently be ignored). If the argument is given as a single string (not in an array reference), that string will be treated as a glob() pattern specifying the files to use.

The default is to look for a test.pl script in the top-level directory of the distribution, and any files matching the glob pattern *.t in the t/ subdirectory. If the recursive_test_files property is true, then the t/ directory will be scanned recursively for *.t files.


Just like pm_files, but used for specifying the set of .xs files in your distribution.


When called from a directory containing a Build.PL script and a META.yml file (in other words, the base directory of a distribution), this method will run the Build.PL and return the resulting Module::Build object to the caller. Any key-value arguments given to new_from_context() are essentially like command line arguments given to the Build.PL script, so for example you could pass verbose => 1 to this method to turn on verbosity.


You'll probably never call this method directly, it's only called from the auto-generated Build script. The new() method is only called once, when the user runs perl Build.PL. Thereafter, when the user runs Build test or another action, the Module::Build object is created using the resume() method to re-instantiate with the settings given earlier to new().


This creates a new Module::Build subclass on the fly, as described in the "SUBCLASSING" section. The caller must provide either a class or code parameter, or both. The class parameter indicates the name to use for the new subclass, and defaults to MyModuleBuilder. The code parameter specifies Perl code to use as the body of the subclass.



Adds a new type of entry to the build process. Accepts a single string specifying its type-name. There must also be a method defined to process things of that type, e.g. if you add a build element called 'foo', then you must also define a method called process_foo_files().

See also "Adding new file types to the build process" in Module::Build::Cookbook.


You may call $self->add_to_cleanup(@patterns) to tell Module::Build that certain files should be removed when the user performs the Build clean action. The arguments to the method are patterns suitable for passing to Perl's glob() function, specified in either Unix format or the current machine's native format. It's usually convenient to use Unix format when you hard-code the filenames (e.g. in Build.PL) and the native format when the names are programmatically generated (e.g. in a testing script).

I decided to provide a dynamic method of the $build object, rather than just use a static list of files named in the Build.PL, because these static lists can get difficult to manage. I usually prefer to keep the responsibility for registering temporary files close to the code that creates them.

  my $args_href = $build->args;
  my %args = $build->args;
  my $arg_value = $build->args($key);
  $build->args($key, $value);

This method is the preferred interface for retrieving the arguments passed via command line options to Build.PL or Build, minus the Module-Build specific options.

When called in in a scalar context with no arguments, this method returns a reference to the hash storing all of the arguments; in an array context, it returns the hash itself. When passed a single argument, it returns the value stored in the args hash for that option key. When called with two arguments, the second argument is assigned to the args hash under the key passed as the first argument.

autosplit_file($from, $to)

Invokes the AutoSplit module on the $from file, sending the output to the lib/auto directory inside $to. $to is typically the blib/ directory.


Returns a string containing the root-level directory of this build, i.e. where the Build.PL script and the lib directory can be found. This is usually the same as the current working directory, because the Build script will chdir() into this directory as soon as it begins execution.


Returns a hash reference indicating the build_requires prerequisites that were passed to the new() method.

check_installed_status($module, $version)

This method returns a hash reference indicating whether a version dependency on a certain module is satisfied. The $module argument is given as a string like "Data::Dumper" or "perl", and the $version argument can take any of the forms described in requires above. This allows very fine-grained version checking.

The returned hash reference has the following structure:

   ok => $whether_the_dependency_is_satisfied,
   have => $version_already_installed,
   need => $version_requested, # Same as incoming $version argument
   message => $informative_error_message,

If no version of $module is currently installed, the have value will be the string "<none>". Otherwise the have value will simply be the version of the installed module. Note that this means that if $module is installed but doesn't define a version number, the have value will be undef - this is why we don't use undef for the case when $module isn't installed at all.

This method may be called either as an object method ($build->check_installed_status($module, $version)) or as a class method (Module::Build->check_installed_status($module, $version)).

check_installed_version($module, $version)

Like check_installed_status(), but simply returns true or false depending on whether module $module satisfies the dependency $version.

If the check succeeds, the return value is the actual version of $module installed on the system. This allows you to do the following:

  my $installed = $build->check_installed_version('DBI', '1.15');
  if ($installed) {
    print "Congratulations, version $installed of DBI is installed.\n";
  } else {
    die "Sorry, you must install DBI.\n";

If the check fails, we return false and set $@ to an informative error message.

If $version is any non-true value (notably zero) and any version of $module is installed, we return true. In this case, if $module doesn't define a version, or if its version is zero, we return the special value "0 but true", which is numerically zero, but logically true.

In general you might prefer to use check_installed_status if you need detailed information, or this method if you just need a yes/no answer.

compare_versions($v1, $op, $v2)

Compares two module versions $v1 and $v2 using the operator $op, which should be one of Perl's numeric operators like != or >= or the like. We do at least a halfway-decent job of handling versions that aren't strictly numeric, like 0.27_02, but exotic stuff will likely cause problems.

In the future, the guts of this method might be replaced with a call out to version.pm.


Returns a hash reference containing the Config.pm hash, including any changes the author or user has specified. This is a reference to the actual internal hash we use, so you probably shouldn't modify stuff there.

config_data($name => $value)

With a single argument, returns the value of the configuration variable $name. With two arguments, sets the given configuration variable to the given value. The value may be any perl scalar that's serializable with Data::Dumper. For instance, if you write a module that can use a MySQL or PostgreSQL back-end, you might create configuration variables called mysql_connect and postgres_connect, and set each to an array of connection parameters for DBI->connect().

Configuration values set in this way using the Module::Build object will be available for querying during the build/test process and after installation via the generated ...::ConfigData module, as ...::ConfigData->config($name).

The feature() and config_data() methods represent Module::Build's main support for configuration of installed modules. See also "SAVING CONFIGURATION INFORMATION".


Returns a hash reference indicating the conflicts prerequisites that were passed to the new() method.


[Deprecated] Please see Module::Build::ModuleInfo instead.

Returns true if the given file appears to contain POD documentation. Currently this checks whether the file has a line beginning with '=pod', '=head', or '=item', but the exact semantics may change in the future.


Takes the file in the from parameter and copies it to the file in the to parameter, or the directory in the to_dir parameter, if the file has changed since it was last copied (or if it doesn't exist in the new location). By default the entire directory structure of from will be copied into to_dir; an optional flatten parameter will copy into to_dir without doing so.

Returns the path to the destination file, or undef if nothing needed to be copied.

Any directories that need to be created in order to perform the copying will be automatically created.


Creates an executable script called Build in the current directory that will be used to execute further user actions. This script is roughly analogous (in function, not in form) to the Makefile created by ExtUtils::MakeMaker. This method also creates some temporary data in a directory called _build/. Both of these will be removed when the realclean action is performed.


Returns the name of the currently-running action, such as "build" or "test". This action is not necessarily the action that was originally invoked by the user. For example, if the user invoked the "test" action, current_action() would initially return "test". However, action "test" depends on action "code", so current_action() will return "code" while that dependency is being executed. Once that action has completed, current_action() will again return "test".

If you need to know the name of the original action invoked by the user, see invoked_action() below.


Invokes the named action or list of actions in sequence. Using this method is preferred to calling the action explicitly because it performs some internal record-keeping, and it ensures that the same action is not invoked multiple times (note: in future versions of Module::Build it's conceivable that this run-only-once mechanism will be changed to something more intelligent).

Note that the name of this method is something of a misnomer; it should really be called something like invoke_actions_unless_already_invoked() or something, but for better or worse (perhaps better!) we were still thinking in make-like dependency terms when we created this method.

See also dispatch(). The main distinction between the two is that depends_on() is meant to call an action from inside another action, whereas dispatch() is meant to set the very top action in motion.

dir_contains($first_dir, $second_dir)

Returns true if the first directory logically contains the second directory. This is just a convenience function because File::Spec doesn't really provide an easy way to figure this out (but Path::Class does...).

dispatch($action, %args)

Invokes the build action $action. Optionally, a list of options and their values can be passed in. This is equivalent to invoking an action at the command line, passing in a list of options.

Custom options that have not been registered must be passed in as a hash reference in a key named "args":

  $build->dispatch('foo', verbose => 1, args => { my_option => 'value' });

This method is intended to be used to programmatically invoke build actions, e.g. by applications controlling Module::Build-based builds rather than by subclasses.

See also depends_on(). The main distinction between the two is that depends_on() is meant to call an action from inside another action, whereas dispatch() is meant to set the very top action in motion.


Returns the name of the directory that will be created during the dist action. The name is derived from the dist_name and dist_version properties.


Returns the name of the current distribution, as passed to the new() method in a dist_name or modified module_name parameter.


Returns the version of the current distribution, as determined by the new() method from a dist_version, dist_version_from, or module_name parameter.

do_system($cmd, @args)

This is a fairly simple wrapper around Perl's system() built-in command. Given a command and an array of optional arguments, this method will print the command to STDOUT, and then execute it using Perl's system(). It returns true or false to indicate success or failure (the opposite of how system() works, but more intuitive).

Note that if you supply a single argument to do_system(), it will/may be processed by the systems's shell, and any special characters will do their special things. If you supply multiple arguments, no shell will get involved and the command will be executed directly.

feature($name => $value)

With a single argument, returns true if the given feature is set. With two arguments, sets the given feature to the given boolean value. In this context, a "feature" is any optional functionality of an installed module. For instance, if you write a module that could optionally support a MySQL or PostgreSQL backend, you might create features called mysql_support and postgres_support, and set them to true/false depending on whether the user has the proper databases installed and configured.

Features set in this way using the Module::Build object will be available for querying during the build/test process and after installation via the generated ...::ConfigData module, as ...::ConfigData->feature($name).

The feature() and config_data() methods represent Module::Build's main support for configuration of installed modules. See also "SAVING CONFIGURATION INFORMATION".


Returns true if the current system seems to have a working C compiler. We currently determine this by attempting to compile a simple C source file and reporting whether the attempt was successful.


Returns the directory in which items of type $type (e.g. lib, arch, bin, or anything else returned by the install_types() method) will be installed during the install action. Any settings for install_path, install_base, and prefix are taken into account when determining the return value.


Returns a list of installable types that this build knows about. These types each correspond to the name of a directory in blib/, and the list usually includes items such as lib, arch, bin, script, libdoc, bindoc, and if HTML documentation is to be built, libhtml and binhtml. Other user-defined types may also exist.


This is the name of the original action invoked by the user. This value is set when the user invokes Build.PL, the Build script, or programatically through the dispatch() method. It does not change as sub-actions are executed as dependencies are evaluated.

To get the name of the currently executing dependency, see current_action() above.

notes($key => $value)

The notes() value allows you to store your own persistent information about the build, and to share that information among different entities involved in the build. See the example in the current() method.

The notes() method is essentally a glorified hash access. With no arguments, notes() returns the entire hash of notes. With one argument, notes($key) returns the value associated with the given key. With two arguments, notes($key, $value) sets the value associated with the given key to $value.

The lifetime of the notes data is for "a build" - that is, the notes hash is created when perl Build.PL is run (or when the new() method is run, if the Module::Build Perl API is being used instead of called from a shell), and lasts until perl Build.PL is run again or the clean action is run.


Returns a string containing the working directory that was in effect before the Build script chdir()-ed into the base_dir. This might be useful for writing wrapper tools that might need to chdir() back out.

rscan_dir($dir, $pattern)

Uses File::Find to traverse the directory $dir, returning a reference to an array of entries matching $pattern. $pattern may either be a regular expression (using qr// or just a plain string), or a reference to a subroutine that will return true for wanted entries. If $pattern is not given, all entries will be returned.


 # All the *.pm files in lib/
 $m->rscan_dir('lib', qr/\.pm$/)
 # All the files in blib/ that aren't *.html files
 $m->rscan_dir('blib', sub {-f $_ and not /\.html$/});

 # All the files in t/

The runtime_params() method stores the values passed on the command line for valid properties (that is, any command line options for which valid_property() returns a true value). The value on the command line may override the default value for a property, as well as any value specified in a call to new(). This allows you to programmatically tell if perl Build.PL or any execution of ./Build had command line options specified that override valid properties.

The runtime_params() method is essentally a glorified read-only hash. With no arguments, runtime_params() returns the entire hash of properties specified on the command line. With one argument, runtime_params($key) returns the value associated with the given key.

The lifetime of the runtime_params data is for "a build" - that is, the runtime_params hash is created when perl Build.PL is run (or when the new() method is called, if the Module::Build Perl API is being used instead of called from a shell), and lasts until perl Build.PL is run again or the clean action is run.


If you're subclassing Module::Build and some code needs to alter its behavior based on the current platform, you may only need to know whether you're running on Windows, Unix, MacOS, VMS, etc., and not the fine-grained value of Perl's $^O variable. The os_type() method will return a string like Windows, Unix, MacOS, VMS, or whatever is appropriate. If you're running on an unknown platform, it will return undef - there shouldn't be many unknown platforms though.


This method is provided for authors to override to customize the fields of META.yml. It is passed a YAML::Node node object which can be modified as desired and then returned. E.g.

  package My::Builder;
  use base 'Module::Build';

  sub prepare_metadata {
    my $self = shift;
    my $node = $self->SUPER::prepare_metadata( shift );
    $node->{custom_field} = 'foo';
    return $node;

Returns a data structure containing information about any failed prerequisites (of any of the types described above), or undef if all prerequisites are met.

The data structure returned is a hash reference. The top level keys are the type of prerequisite failed, one of "requires", "build_requires", "conflicts", or "recommends". The associated values are hash references whose keys are the names of required (or conflicting) modules. The associated values of those are hash references indicating some information about the failure. For example:

   have => '0.42',
   need => '0.59',
   message => 'Version 0.42 is installed, but we need version 0.59',


   have => '<none>',
   need => '0.59',
   message => 'Prerequisite Foo isn't installed',

This hash has the same structure as the hash returned by the check_installed_status() method, except that in the case of "conflicts" dependencies we change the "need" key to "conflicts" and construct a proper message.


  # Check a required dependency on Foo::Bar
  if ( $build->prereq_failures->{requires}{Foo::Bar} ) { ...

  # Check whether there were any failures
  if ( $build->prereq_failures ) { ...

  # Show messages for all failures
  my $failures = $build->prereq_failures;
  while (my ($type, $list) = each %$failures) {
    while (my ($name, $hash) = each %$list) {
      print "Failure for $name: $hash->{message}\n";

Returns a human-readable (table-form) string showing all prerequisites, the versions required, and the versions actually installed. This can be useful for reviewing the configuration of your system prior to a build, or when compiling data to send for a bug report. The prereq_report action is just a thin wrapper around the prereq_report() method.

prompt($message, $default)

Asks the user a question and returns their response as a string. The first argument specifies the message to display to the user (for example, "Where do you keep your money?"). The second argument, which is optional, specifies a default answer (for example, "wallet"). The user will be asked the question once.

If the current session doesn't seem to be interactive (i.e. if STDIN and STDOUT look like they're attached to files or something, not terminals), we'll just use the default without letting the user provide an answer.

This method may be called as a class or object method.


Returns a hash reference indicating the recommends prerequisites that were passed to the new() method.


Returns a hash reference indicating the requires prerequisites that were passed to the new() method.


Returns a hash reference whose keys are the perl script files to be installed, if any. This corresponds to the script_files parameter to the new() method. With an optional argument, this parameter may be set dynamically.

For backward compatibility, the scripts() method does exactly the same thing as script_files(). scripts() is deprecated, but it will stay around for several versions to give people time to transition.

up_to_date($source_file, $derived_file)
up_to_date(\@source_files, \@derived_files)

This method can be used to compare a set of source files to a set of derived files. If any of the source files are newer than any of the derived files, it returns false. Additionally, if any of the derived files do not exist, it returns false. Otherwise it returns true.

The arguments may be either a scalar or an array reference of file names.

y_n($message, $default)

Asks the user a yes/no question using prompt() and returns true or false accordingly. The user will be asked the question repeatedly until they give an answer that looks like "yes" or "no".

The first argument specifies the message to display to the user (for example, "Shall I invest your money for you?"), and the second argument specifies the default answer (for example, "y").

Note that the default is specified as a string like "y" or "n", and the return value is a Perl boolean value like 1 or 0. I thought about this for a while and this seemed like the most useful way to do it.

This method may be called as a class or object method.

Autogenerated Accessors

In addition to the aforementioned methods, there are also some get/set accessor methods for the following properties:



There are three basic types of prerequisites that can be defined: 1) "requires" - are versions of modules that are required for certain functionality to be available; 2) "recommends" - are versions of modules that are recommended to provide enhanced functionality; and 3) "conflicts" - are versions of modules that conflict with, and that can cause problems with the distribution.

Each of the three types of prerequisites listed above can be applied to different aspects of the Build process. For the module distribution itself you simply define "requires", "recommends", or "conflicts". The types can also apply to other aspects of the Build process. Currently, only "build_requires" is defined which is used for modules which are required during the Build process.

Format of prerequisites

The prerequisites are given in a hash reference, where the keys are the module names and the values are version specifiers:

  requires => {
               Foo::Module => '2.4',
               Bar::Module => 0,
               Ken::Module => '>= 1.2, != 1.5, < 2.0',
               perl => '5.6.0'

These four version specifiers have different effects. The value '2.4' means that at least version 2.4 of Foo::Module must be installed. The value 0 means that any version of Bar::Module is acceptable, even if Bar::Module doesn't define a version. The more verbose value '>= 1.2, != 1.5, < 2.0' means that Ken::Module's version must be at least 1.2, less than 2.0, and not equal to 1.5. The list of criteria is separated by commas, and all criteria must be satisfied.

A special perl entry lets you specify the versions of the Perl interpreter that are supported by your module. The same version dependency-checking semantics are available, except that we also understand perl's new double-dotted version numbers.


Module::Build provides a very convenient way to save configuration information that your installed modules (or your regression tests) can access. If your Build process calls the feature() or config_data() methods, then a Foo::Bar::ConfigData module will automatically be created for you, where Foo::Bar is the module_name parameter as passed to new(). This module provides access to the data saved by these methods, and a way to update the values. There is also a utility script called config_data distributed with Module::Build that provides a command line interface to this same functionality. See also the generated Foo::Bar::ConfigData documentation, and the config_data script's documentation, for more information.


One advantage of Module::Build is that since it's implemented as Perl methods, you can invoke these methods directly if you want to install a module non-interactively. For instance, the following Perl script will invoke the entire build/install procedure:

  my $build = Module::Build->new(module_name => 'MyModule');

If any of these steps encounters an error, it will throw a fatal exception.

You can also pass arguments as part of the build process:

  my $build = Module::Build->new(module_name => 'MyModule');
  $build->dispatch('test', verbose => 1);
  $build->dispatch('install', sitelib => '/my/secret/place/');

Building and installing modules in this way skips creating the Build script.


Module::Build creates a class hierarchy conducive to customization. Here is the parent-child class hierarchy in classy ASCII art:

   |   Your::Parent     |  (If you subclass Module::Build)
   /--------------------\  (Doesn't define any functionality
   |   Module::Build    |   of its own - just figures out what
   \--------------------/   other modules to load.)
   /-----------------------------------\  (Some values of $^O may
   |   Module::Build::Platform::$^O    |   define specialized functionality.
   \-----------------------------------/   Otherwise it's ...::Default, a
            |                              pass-through class.)
   |   Module::Build::Base    |  (Most of the functionality of 
   \--------------------------/   Module::Build is defined here.)


Right now, there are two ways to subclass Module::Build. The first way is to create a regular module (in a .pm file) that inherits from Module::Build, and use that module's class instead of using Module::Build directly:

  ------ in Build.PL: ----------

  use lib q(/nonstandard/library/path);
  use My::Builder;  # Or whatever you want to call it

  my $build = My::Builder->new
     module_name => 'Foo::Bar',  # All the regular args...
     license     => 'perl',
     dist_author => 'A N Other <me@here.net.au>',
     requires    => { Carp => 0 }

This is relatively straightforward, and is the best way to do things if your My::Builder class contains lots of code. The create_build_script() method will ensure that the current value of @INC (including the /nonstandard/library/path) is propogated to the Build script, so that My::Builder can be found when running build actions.

For very small additions, Module::Build provides a subclass() method that lets you subclass Module::Build more conveniently, without creating a separate file for your module:

  ------ in Build.PL: ----------

  use Module::Build;
  my $class = Module::Build->subclass
     class => 'My::Builder',
     code => q{
       sub ACTION_foo {
         print "I'm fooing to death!\n";

  my $build = $class->new
     module_name => 'Foo::Bar',  # All the regular args...
     license     => 'perl',
     dist_author => 'A N Other <me@here.net.au>',
     requires    => { Carp => 0 }

Behind the scenes, this actually does create a .pm file, since the code you provide must persist after Build.PL is run if it is to be very useful.

See also the documentation for the subclass() method.


When starting development on a new module, it's rarely worth your time to create a tree of all the files by hand. Some automatic module-creators are available: the oldest is h2xs, which has shipped with perl itself for a long time. Its name reflects the fact that modules were originally conceived of as a way to wrap up a C library (thus the h part) into perl extensions (thus the xs part).

These days, h2xs has largely been superseded by modules like ExtUtils::ModuleMaker, Module::Starter, and Module::Maker. They have varying degrees of support for Module::Build.


Note that if you want to provide both a Makefile.PL and a Build.PL for your distribution, you probably want to add the following to WriteMakefile in your Makefile.PL so that MakeMaker doesn't try to run your Build.PL as a normal .PL file:

  PL_FILES => {},

You may also be interested in looking at the Module::Build::Compat module, which can automatically create various kinds of Makefile.PL compatibility layers.


Ken Williams, kwilliams@cpan.org

Development questions, bug reports, and patches should be sent to the Module-Build mailing list at module-build-general@lists.sourceforge.net .

Bug reports are also welcome at http://rt.cpan.org/NoAuth/Bugs.html?Dist=Module-Build .

An anonymous CVS repository containing the latest development version is available; see http://sourceforge.net/cvs/?group_id=45731 for the details of how to access it.


perl(1), Module::Build(3), Module::Build::Cookbook(3), ExtUtils::MakeMaker(3), YAML(3)

META.yml Specification: http://module-build.sourceforge.net/META-spec-v1.2.html