Module::Build - Build and install Perl modules


Module::Build - Build and install Perl modules


Standard process for building & installing modules:

   perl Build.PL
   ./Build test
   ./Build install

Or, if you're on a platform (like DOS or Windows) that doesn't like the ``./'' notation, you can do this:

   perl Build.PL
   perl Build
   perl Build test
   perl Build install


Module::Build is a system for building, testing, and installing Perl modules. It is meant to be an alternative to ExtUtils::MakeMaker. Developers may alter the behavior of the module through subclassing in a much more straightforward way than with MakeMaker. It also does not require a make on your system - most of the Module::Build code is pure-perl and written in a very cross-platform way. In fact, you don't even need a shell, so even platforms like MacOS (traditional) can use it fairly easily. Its only prerequisites are modules that are included with perl 5.6.0, and it works fine on perl 5.005 if you can install a few additional modules.

See MOTIVATIONS for more comparisons between ExtUtils::MakeMaker and Module::Build.

To install Module::Build, and any other module that uses Module::Build for its installation process, do the following:

  perl Build.PL       # 'Build.PL' script creates the 'Build' script
  ./Build             # Need ./ to ensure we're using this "Build" script
  ./Build test        # and not another one that happens to be in the PATH
  ./Build install

This illustrates initial configuration and the running of three 'actions'. In this case the actions run are 'build' (the default action), 'test', and 'install'. Other actions defined so far include:

  build                          fakeinstall 
  config_data                    help        
  clean                          html        
  code                           install     
  diff                           manifest    
  dist                           ppd         
  distcheck                      ppmdist     
  distclean                      realclean   
  distdir                        skipcheck   
  distmeta                       test        
  distsign                       testcover   
  disttest                       testdb      
  docs                           versioninstall

You can run the 'help' action for a complete list of actions.

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 the Module::Build::Compat manpage and


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.

Creates a new Module::Build object. Arguments to the new() method are listed below. Unless otherwise documented, there's also a corresponding get/set method on the Module::Build object to access their values. 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.
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/ dist_version_from will in turn be used to set dist_version.

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

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 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.

Specifies the licensing terms of your distribution. Valid options include:
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 is distributed under the terms of the Gnu General Public License (

The distribution is distributed under the terms of the Gnu Lesser General Public License (

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 (

The distribution is licensed under some other Open Source Initiative-approved license listed at .

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

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

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.

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.

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

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 now a recommends section for things that aren't absolutely required.

Automated tools like 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 sysnonym 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.

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 will be skipped if recommended dependencies aren't present.

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

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.

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.

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 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 true, this parameter tells Module::Build to create a .packlist file during the install action, just like ExtUtils::MakeMaker does. The file is created in a subdirectory of the arch installation location. It is used by some other tools (CPAN, CPANPLUS, etc.) for determining what files are part of an install.

The default value is true. This parameter was introduced in Module::Build version 0.2609; previously no packlists were ever created by Module::Build.

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.

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 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 => { '' => 'lib/Foo/' },

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.

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

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/ might create the file lib/Foo/

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/' => 'lib/',
                   'lib/Foo.PL' => [ 'lib/', 'lib/' ],

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

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.

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 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.

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.

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 to do something useful with it. It can potentially bring lots of security, packaging, and convenience improvements.

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

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.

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          => 'Spangly',
     extra_compiler_flags => ['-x', 'c++'],

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

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

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.

This should be something like ``John Doe <>'', 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.

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

For each feature named, the prerequisite options 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).

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 has returned by args(). For example:

 my $loud = 0;
 my $build = Module::Build->new(
     module_name => 'Spangly',
     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.

  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 retreiving 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.

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.

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.

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.

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 reinstantiate with the settings given earlier to new().

This method returns a reasonable faxsimile 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.

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 a reference to 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 hash reference containing the 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.

dispatch($action, %args)
This method is also called from the auto-generated Build script. It parses the command-line arguments into an action and an argument list, then calls the appropriate routine to handle the action. Currently (though this may change), an action foo will invoke the ACTION_foo method. All arguments (including everything mentioned in ACTIONS below) are contained in the $self->{args} hash reference.

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.

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 ( $m->prereq_failures->{requires}{Foo::Bar} ) { ...
  # Check whether there were any failures
  if ( $m->prereq_failures ) { ...

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

Each of these methods returns a hash reference indicating the 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 statisfies 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 = $m->check_installed_version('DBI', '1.15');
 if ($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 nontrue 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.

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.

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.

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.

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 elements to the build process in the Module::Build::Cookbook manpage.

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.

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.

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 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 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.

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.

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.

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.

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 backend, 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.


There are some general principles at work here. First, each task when building a module is called an ``action''. These actions are listed above; they correspond to the building, testing, installing, packaging, etc. tasks.

Second, arguments are processed in a very systematic way. Arguments are always key=value pairs. They may be specified at perl Build.PL time (i.e. perl Build.PL destdir=/my/secret/place), in which case their values last for the lifetime of the Build script. They may also be specified when executing a particular action (i.e. Build test verbose=1), in which case their values last only for the lifetime of that command. Per-action command-line parameters take precedence over parameters specified at perl Build.PL time.

The build process also relies heavily on the module, and all the key=value pairs in are available in

$self->{config}. If the user wishes to override any of the values in, she may specify them like so:

  perl Build.PL --config cc=gcc --config ld=gcc

The following build actions are provided by default.

This action will simply print out a message that is meant to help you use the build process. It will show you a list of available build actions too.

With an optional argument specifying an action name (e.g. Build help test), the 'help' action will show you any POD documentation it can find for that action.

If you run the Build script without any arguments, it runs the build action, which in turn runs the code and docs actions.

This is analogous to the MakeMaker 'make all' target.

This action builds your codebase.

By default it just creates a blib/ directory and copies any .pm and .pod files from your lib/ directory into the blib/ directory. It also compiles any .xs files from lib/ and places them in blib/. Of course, you need a working C compiler (probably the same one that built perl itself) for the compilation to work properly.

The build action also runs any .PL files in your lib/ directory. Typically these create other files, named the same but without the .PL ending. For example, a file lib/Foo/ could create the file lib/Foo/ The .PL files are processed first, so any .pm files (or other kinds that we deal with) will get copied correctly.

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 should tell us that so that we can clean up properly after these created files. Use the PL_files parameter to new():

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

Note that in contrast to MakeMaker, the build action only (currently) handles .pm, .pod, .PL, and .xs files. They must all be in the lib/ directory, in the directory structure that they should have when installed. We also handle .c files that can be in the place of your choosing - see the c_source argument to new().

The .xs support is currently in alpha. Please let me know whether it works for you.

This will generate documentation (ie: Unix man pages) for any binary and library files under blib/ that contain POD. If there are no bindoc or libdoc installation targets defined (as will be the case on systems that don't support Unix manpages) this action does nothing.

This will use Test::Harness to run any regression tests and report their results. Tests can be defined in the standard places: a file called in the top-level directory, or several files ending with .t in a t/ directory.

If you want tests to be 'verbose', i.e. show details of test execution rather than just summary information, pass the argument verbose=1.

If you want to run tests under the perl debugger, pass the argument debugger=1.

In addition, if a file called exists in the top-level directory, this file will be executed as a Perl script and its output will be shown to the user. This is a good place to put speed tests or other tests that don't use the Test::Harness format for output.

To override the choice of tests to run, you may pass a test_files argument whose value is a whitespace-separated list of test scripts to run. This is especially useful in development, when you only want to run a single test to see whether you've squashed a certain bug yet:

 ./Build test --test_files t/something_failing.t

You may also pass several test_files arguments separately:

 ./Build test --test_files t/one.t --test_files t/two.t

or use a glob()-style pattern:

 ./Build test --test_files 't/01-*.t'

Runs the test action using Devel::Cover, generating a code-coverage report showing which parts of the code were actually exercised during the tests.

To pass options to Devel::Cover, set the $DEVEL_COVER_OPTIONS environment variable:

  DEVEL_COVER_OPTIONS=-ignore,Build ./Build testcover

This is a synonym for the 'test' action with the debugger=1 argument.

This checks all the files described in the docs action and produces Test::Harness-style output. If you are a module author, this is useful to run before creating a new release.

This action will clean up any files that the build process may have created, including the blib/ directory (but not including the _build/ directory and the Build script itself).

This action is just like the clean action, but also removes the _build directory and the Build script. If you run the realclean action, you are essentially starting over, so you will have to re-create the Build script again.

This action will compare the files about to be installed with their installed counterparts. For .pm and .pod files, a diff will be shown (this currently requires a 'diff' program to be in your PATH). For other files like compiled binary files, we simply report whether they differ.

A flags parameter may be passed to the action, which will be passed to the 'diff' program. Consult your 'diff' documentation for the parameters it will accept - a good one is -u:

 ./Build diff flags=-u

This action will use ExtUtils::Install to install the files from blib/ into the system. See How Installation Paths are Determined for details about how Module::Build determines where to install things, and how to influence this process.

If you want the installation process to look around in @INC for other versions of the stuff you're installing and try to delete it, you can use the uninst parameter, which tells ExtUtils::Install to do so:

 Build install uninst=1

This can be a good idea, as it helps prevent multiple versions of a module from being present on your system, which can be a confusing situation indeed.

This is just like the install action, but it won't actually do anything, it will just report what it would have done if you had actually run the install action.

** Note: since is so new, and since we just recently added support for it here too, this feature is to be considered experimental. **

If you have the module installed on your system, you can use this action to install a module into the version-specific library trees. This means that you can have several versions of the same module installed and use a specific one like this:

 use only MyModule => 0.55;

To override the default installation libraries in only::config, specify the versionlib parameter when you run the Build.PL script:

 perl Build.PL versionlib=/my/version/place/

To override which version the module is installed as, specify the versionlib parameter when you run the Build.PL script:

 perl Build.PL version=0.50

See the documentation for more information on version-specific installs.

This is an action intended for use by module authors, not people installing modules. It will bring the MANIFEST up to date with the files currently present in the distribution. You may use a MANIFEST.SKIP file to exclude certain files or directories from inclusion in the MANIFEST. MANIFEST.SKIP should contain a bunch of regular expressions, one per line. If a file in the distribution directory matches any of the regular expressions, it won't be included in the MANIFEST.

The following is a reasonable MANIFEST.SKIP starting point, you can add your own stuff to it:


See the distcheck and skipcheck actions if you want to find out what the manifest action would do, without actually doing anything.

This action is helpful for module authors who want to package up their module for source distribution through a medium like CPAN. It will create a tarball of the files listed in MANIFEST and compress the tarball using GZIP compression.

By default, this action will use the external tar and gzip executables on Unix-like platforms, and the Archive::Tar module elsewhere. However, you can force it to use whatever executable you want by supplying an explicit tar (and optional gzip) parameter:

 perl Build dist --tar C:\path\to\tar.exe --gzip C:\path\to\zip.exe

Generates a PPM binary distribution and a PPD description file. This action also invokes the 'ppd' action, so it can accept the same codebase argument described under that action.

This uses the same mechanism as the dist action to tar & zip its output, so you can supply tar and/or gzip parameters to affect the result.

Uses Module::Signature to create a SIGNATURE file for your distribution, and adds the SIGNATURE file to the distribution's MANIFEST.

Creates the META.yml file for your distribution.

Reports which files are in the build directory but not in the MANIFEST file, and vice versa. (See manifest for details)

Reports which files are skipped due to the entries in the MANIFEST.SKIP file (See manifest for details)

Performs the 'realclean' action and then the 'distcheck' action.

Creates a directory called $(DISTNAME)-$(VERSION) (if that directory already exists, it will be removed first). Then copies all the files listed in the MANIFEST file to that directory. This directory is what people will see when they download your distribution and unpack it.

While performing the 'distdir' action, a file containing various bits of ``metadata'' will be created. The metadata includes the module's name, version, dependencies, license, and the dynamic_config flag. This file is created as META.yml in YAML format, so you must have the YAML module installed in order to create it. You should also ensure that the META.yml file is listed in your MANIFEST - if it's not, a warning will be issued.

Performs the 'distdir' action, then switches into that directory and runs a perl Build.PL, followed by the 'build' and 'test' actions in that directory.

Build a PPD file for your distribution.

This action takes an optional argument codebase which is used in the generated ppd file to specify the (usually relative) URL of the distribution. By default, this value is the distribution name without any path information.


 perl Build ppd codebase="MSWin32-x86-multi-thread/Module-Build-0.21.tar.gz"

How Installation Paths are Determined

When you invoke Module::Build's build action, it needs to figure out where to install things. The nutshell version of how this works is that default installation locations are determined from, and they may be overridden by using the install_path parameter. An install_base parameter lets you specify an alternative installation root like /home/foo, and a destdir lets you specify a temporary installation directory like /tmp/install in case you want to create bundled-up installable packages.

Natively, Module::Build provides default installation locations for the following types of installable items:

Usually pure-Perl module files ending in .pm.

``Architecture-dependent'' module files, usually produced by compiling XS, Inline, or similar code.

Programs written in pure Perl. In order to improve reuse, try to make these as small as possible - put the code into modules whenever possible.

``Architecture-dependent'' executable programs, i.e. compiled C code or something. Pretty rare to see this in a perl distribution, but it happens.

Documentation for the stuff in lib and arch. This is usually generated from the POD in .pm files. Under Unix, these are manual pages belonging to the 'man3' category.

Documentation for the stuff in script and bin. Usually generated from the POD in those files. Under Unix, these are manual pages belonging to the 'man1' category.

Four other parameters let you control various aspects of how installation paths are determined:

The default destinations for these installable things come from entries in your system's You can select from three different sets of default locations by setting the installdirs parameter as follows:
                          'installdirs' set to:
                   core          site                vendor

              uses the following defaults from

 lib     => installprivlib  installsitelib      installvendorlib
 arch    => installarchlib  installsitearch     installvendorarch
 script  => installscript   installsitebin      installvendorbin
 bin     => installbin      installsitebin      installvendorbin
 libdoc  => installman3dir  installsiteman3dir  installvendorman3dir
 bindoc  => installman1dir  installsiteman1dir  installvendorman1dir

The default value of installdirs is ``site''. If you're creating vendor distributions of module packages, you may want to do something like this:

 perl Build.PL installdirs=vendor


 Build install installdirs=vendor

If you're installing an updated version of a module that was included with perl itself (i.e. a ``core module''), then you may set installdirs to ``core'' to overwrite the module in its present location.

(Note that the 'script' line is different from MakeMaker - unfortunately there's no such thing as ``installsitescript'' or ``installvendorscript'' entry in, so we use the ``installsitebin'' and ``installvendorbin'' entries to at least get the general location right. In the future, if adds some more appropriate entries, we'll start using those.)

Once the defaults have been set, you can override them. You can set individual entries by using the install_path parameter:
 my $m = Module::Build->new
  (...other options...,
   install_path => {lib  => '/foo/lib',
                    arch => '/foo/lib/arch'});

On the command line, that would look like this:

 perl Build.PL --install_path lib=/foo/lib --install_path arch=/foo/lib/arch

or this:

 Build install --install_path lib=/foo/lib --install_path arch=/foo/lib/arch

You can also set the whole bunch of installation paths by supplying the install_base parameter to point to a directory on your system. For instance, if you set install_base to ``/home/ken'' on a Linux system, you'll install as follows:
 lib     => /home/ken/lib
 arch    => /home/ken/lib/i386-linux
 script  => /home/ken/scripts
 bin     => /home/ken/bin
 bindoc  => /home/ken/man/man1
 libdoc  => /home/ken/man/man3

Note that this is different from how MakeMaker's PREFIX parameter works. PREFIX tries to create a mini-replica of a site-style installation under the directory you specify, which is not always possible (and the results are not always pretty in this case). install_base just gives you a default layout under the directory you specify, which may have little to do with the installdirs=site layout.

The exact layout under the directory you specify may vary by system - we try to do the ``sensible'' thing on each platform.

If you want to install everything into a temporary directory first (for instance, if you want to create a directory tree that a package manager like rpm or dpkg could create a package from), you can use the destdir parameter:
 perl Build.PL destdir=/tmp/foo


 Build install destdir=/tmp/foo

This will effectively install to ``/tmp/foo/$sitelib'', ``/tmp/foo/$sitearch'', and the like, except that it will use File::Spec to make the pathnames work correctly on whatever platform you're installing on.


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 $m = 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 $m = Module::Build->new(module_name => 'MyModule');
 $m->dispatch('test', verbose => 1);
 $m->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 qw(/nonstandard/library/path);
  use My::Builder;  # Or whatever you want to call it

  my $m = My::Builder->new
    (module_name=> 'Next::Big::Thing',  # All the regular args...
     license=> 'perl',
     dist_author=> 'A N Other <>',
     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 $m = $class->new
    (module_name=> 'Next::Big::Thing',  # All the regular args...
     license=> 'perl',
     dist_author=> 'A N Other <>',
     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.


There are several reasons I wanted to start over, and not just fix what I didn't like about MakeMaker:


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.


The current method of relying on time stamps to determine whether a derived file is out of date isn't likely to scale well, since it requires tracing all dependencies backward, it runs into problems on NFS, and it's just generally flimsy. It would be better to use an MD5 signature or the like, if available. See cons for an example.

- append to perllocal.pod - write .packlist in appropriate location (needed for un-install) - add a 'plugin' functionality


Ken Williams,

Development questions, bug reports, and patches should be sent to the Module-Build mailing list at .

Bug reports are also welcome at .

An anonymous CVS repository containing the latest development version is available; see for the details of how to access it.


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

 Module::Build - Build and install Perl modules