Switch branches/tags
Find file Copy path
Fetching contributors…
Cannot retrieve contributors at this time
346 lines (273 sloc) 11.3 KB


mrbgems is a library manager to integrate C and Ruby extension in an easy and standardised way into mruby.


By default mrbgems is currently deactivated. As soon as you add a GEM to your build configuration (i.e. build_config.rb), mrbgems will be activated and the extension integrated.

To add a GEM into the build_config.rb add the following line for example:

conf.gem '/path/to/your/gem/dir'

You can also use a relative path which would be relative from the mruby root:

conf.gem 'examples/mrbgems/ruby_extension_example'

A remote GIT repository location for a GEM is also supported:

conf.gem :git => '', :branch => 'master'
conf.gem :github => 'masuidrive/mrbgems-example', :branch => 'master'
conf.gem :bitbucket => 'mruby/mrbgems-example', :branch => 'master'

You can specify the sub directory of the repository with :path option:

conf.gem github: 'mruby/mruby', path: 'mrbgems/mruby-socket'

To use mrbgem from mgem-list use :mgem option:

conf.gem :mgem => 'mruby-yaml'
conf.gem :mgem => 'yaml' # 'mruby-' prefix could be omitted

If there is missing dependencies, mrbgem dependencies solver will reference mrbgem from core or mgem-list.

To pull all gems from remote GIT repository on build, call ./minirake -p, or ./minirake --pull-gems.

NOTE: :bitbucket option supports only git. Hg is unsupported in this version.


There are instances when you wish to add a collection of mrbgems into mruby at once, or be able to substitute mrbgems based on configuration, without having to add each gem to the build_config.rb file. A packaged collection of mrbgems is called a GemBox. A GemBox is a file that contains a list of mrbgems to load into mruby, in the same format as if you were adding them to build_config.rb via config.gem, but wrapped in an MRuby::GemBox object. GemBoxes are loaded into mruby via config.gembox 'boxname'.

Below we have created a GemBox containing mruby-time and mrbgems-example: do |conf|
  conf.gem "#{root}/mrbgems/mruby-time"
  conf.gem :github => 'masuidrive/mrbgems-example'

As mentioned, the GemBox uses the same conventions as MRuby::Build. The GemBox must be saved with a .gembox extension inside the mrbgems directory to to be picked up by mruby.

To use this example GemBox, we save it as custom.gembox inside the mrbgems directory in mruby, and add the following to our build_config.rb file inside the build block:

conf.gembox 'custom'

This will cause the custom GemBox to be read in during the build process, adding mruby-time and mrbgems-example to the build.

If you want, you can put GemBox outside of mruby directory. In that case you must specify an absolute path like below.

conf.gembox "#{ENV["HOME"]}/mygemboxes/custom"

There are two GemBoxes that ship with mruby: default and full-core. The default GemBox contains several core components of mruby, and full-core contains every gem found in the mrbgems directory.

GEM Structure

The maximal GEM structure looks like this:

+- GEM_NAME         <- Name of GEM
   +- include/      <- Header for Ruby extension (will exported)
   +- mrblib/       <- Source for Ruby extension
   +- src/          <- Source for C extension
   +- test/         <- Test code (Ruby)
   +- mrbgem.rake   <- GEM Specification
   +-     <- Readme for GEM

The folder mrblib contains pure Ruby files to extend mruby. The folder src contains C/C++ files to extend mruby. The folder include contains C/C++ header files. The folder test contains C/C++ and pure Ruby files for testing purposes which will be used by mrbtest. mrbgem.rake contains the specification to compile C and Ruby files. is a short description of your GEM.

Build process

mrbgems expects a specification file called mrbgem.rake inside of your GEM directory. A typical GEM specification could look like this for example:'c_and_ruby_extension_example') do |spec|
  spec.license = 'MIT'  = 'mruby developers'
  spec.summary = 'Example mrbgem using C and ruby'

The mrbgems build process will use this specification to compile Object and Ruby files. The compilation results will be added to lib/libmruby.a. This file exposes the GEM functionality to tools like mruby and mirb.

The following properties can be set inside of your MRuby::Gem::Specification for information purpose:

  • spec.license or spec.licenses (A single license or a list of them under which this GEM is licensed)
  • or spec.authors (Developer name or a list of them)
  • spec.version (Current version)
  • spec.description (Detailed description)
  • spec.summary
    • One line short description of mrbgem.
    • Printed in build summary of rake when set.
  • spec.homepage (Homepage)
  • spec.requirements (External requirements as information for user)

The license and author properties are required in every GEM!

In case your GEM is depending on other GEMs please use spec.add_dependency(gem, *requirements[, default_get_info]) like:'c_and_ruby_extension_example') do |spec|
  spec.license = 'MIT'  = 'mruby developers'

  # Add GEM dependency mruby-parser.
  # The version must be between 1.0.0 and 1.5.2 .
  spec.add_dependency('mruby-parser', '>= 1.0.0', '<= 1.5.2')

  # Use any version of mruby-uv from github.
  spec.add_dependency('mruby-uv', '>= 0.0.0', :github => 'mattn/mruby-uv')

  # Use latest mruby-onig-regexp from github. (version requirements can be omitted)
  spec.add_dependency('mruby-onig-regexp', :github => 'mattn/mruby-onig-regexp')

  # You can add extra mgems active only on test
  spec.add_test_dependency('mruby-process', :github => 'iij/mruby-process')

The version requirements and default gem information are optional.

Version requirement supports following operators:

  • '=': is equal
  • '!=': is not equal
  • '>': is greater
  • '<': is lesser
  • '>=': is equal or greater
  • '<=': is equal or lesser
  • '~>': is equal or greater and is lesser than the next major version
    • example 1: '~> 2.2.2' means '>= 2.2.2' and '< 2.3.0'
    • example 2: '~> 2.2' means '>= 2.2.0' and '< 3.0.0'

When more than one version requirements is passed, the dependency must satisfy all of it.

You can have default gem to use as depedency when it's not defined in build_config.rb. When the last argument of add_dependency call is Hash, it will be treated as default gem information. Its format is same as argument of method MRuby::Build#gem, expect that it can't be treated as path gem location.

When a special version of depedency is required, use MRuby::Build#gem in build_config.rb to override default gem.

If you have conflicting GEMs use the following method:

  • spec.add_conflict(gem, *requirements)
    • The requirements argument is same as in add_dependency method.

like following code: 'some-regexp-binding' do |spec|
  spec.license = 'BSD' = 'John Doe'

  spec.add_conflict 'mruby-onig-regexp', '> 0.0.0'
  spec.add_conflict 'mruby-hs-regexp'
  spec.add_conflict 'mruby-pcre-regexp'
  spec.add_conflict 'mruby-regexp-pcre'

In case your GEM has more complex build requirements you can use the following options additionally inside of your GEM specification:

  • (C compiler flags)
  • (C compiler defines)
  • (C compiler include paths)
  • spec.linker.flags (Linker flags)
  • spec.linker.libraries (Linker libraries)
  • spec.linker.library_paths (Linker additional library path)
  • spec.bins (Generate binary file)
  • spec.rbfiles (Ruby files to compile)
  • spec.objs (Object files to compile)
  • spec.test_rbfiles (Ruby test files for integration into mrbtest)
  • spec.test_objs (Object test files for integration into mrbtest)
  • spec.test_preload (Initialization files for mrbtest)

You also can use and spec.mruby.linker to add extra global parameters for compiler and linker.

include_paths and dependency

Your GEM can export include paths to another GEMs that depends on your GEM. By default, /...absolute path.../{GEM_NAME}/include will be exported. So it is recommended not to put GEM's local header files on include/.

These exports are retroactive. For example: when B depends to C and A depends to B, A will get include paths exported by C.

Exported include_paths are automatically appended to GEM local include_paths by Minirake. You can use spec.export_include_paths accessor if you want more complex build.

C Extension

mruby can be extended with C. This is possible by using the C API to integrate C libraries into mruby.


mrbgems expects that you have implemented a C method called mrb_YOURGEMNAME_gem_init(mrb_state). YOURGEMNAME will be replaced by the name of your GEM. If you call your GEM c_extension_example, your initialisation method could look like this:

mrb_c_extension_example_gem_init(mrb_state* mrb) {
  struct RClass *class_cextension = mrb_define_module(mrb, "CExtension");
  mrb_define_class_method(mrb, class_cextension, "c_method", mrb_c_method, MRB_ARGS_NONE());


mrbgems expects that you have implemented a C method called mrb_YOURGEMNAME_gem_final(mrb_state). YOURGEMNAME will be replaced by the name of your GEM. If you call your GEM c_extension_example, your finalizer method could look like this:

mrb_c_extension_example_gem_final(mrb_state* mrb) {


+- c_extension_example/
   +- src/
   |  |
   |  +- example.c         <- C extension source
   +- test/
   |  |
   |  +- example.rb        <- Test code for C extension
   +- mrbgem.rake          <- GEM specification

Ruby Extension

mruby can be extended with pure Ruby. It is possible to override existing classes or add new ones in this way. Put all Ruby files into the mrblib folder.




+- ruby_extension_example/
   +- mrblib/
   |  |
   |  +- example.rb        <- Ruby extension source
   +- test/
   |  |
   |  +- example.rb        <- Test code for Ruby extension
   +- mrbgem.rake          <- GEM specification

C and Ruby Extension

mruby can be extended with C and Ruby at the same time. It is possible to override existing classes or add new ones in this way. Put all Ruby files into the mrblib folder and all C files into the src folder.

mruby codes under mrblib directory would be executed after gem init C function is called. Make sure mruby script depends on C code and C code doesn't depend on mruby script.


See C and Ruby example.


+- c_and_ruby_extension_example/
   +- mrblib/
   |  |
   |  +- example.rb        <- Ruby extension source
   +- src/
   |  |
   |  +- example.c         <- C extension source
   +- test/
   |  |
   |  +- example.rb        <- Test code for C and Ruby extension
   +- mrbgem.rake          <- GEM specification