mruby CLI

A utility for setting up a CLI with mruby that compiles binaries to Linux, OS X, and Windows.


You'll need the following installed and in your PATH:

On Mac OS X and Windows, Docker Toolbox is the recommended way to install Docker and docker-compose (does not work on windows).

Building a CLI app

To generate a new mruby CLI, there's a --setup option.

$ mruby-cli --setup <app name>

This will generate a folder <app name> containing a basic skeleton for getting started. Once you're in the folder, you can build all the binaries:

$ docker-compose run compile

You'll be able to find the binaries in the following directories:

You should be able to run the respective binary that's native on your platform. There's a shell service that can be used as well. In the example below, mruby-cli --setup hello_world was run.

$ docker-compose run shell
root@3da278e931fc:/home/mruby/code# mruby/build/host/bin/hello_world
Hello World


Each app will be generated with a Dockerfile that inherits a base image.

You can pull the image from docker hub here:

The Dockerfile for the base image is available on github:

Hello World

Building the canonical hello world example in mruby-cli is quite simple. The two files of note from the generate skeleton are mrblib/hello_world.rb and mrbgem.rake. The CLI hooks into the __main__ method defined here and passes all the arguments as argv.


def __main__(argv)
  puts "Hello World"


The rubygems equivalent is mrbgems. mgem-list contains a list of mgems you can pull from. By default mruby does not include everything in the kitchen sink like MRI. This means to even get puts, we need to include the mruby-print. The list of core gems can be found here. Adding dependencies is simple, you just need to add a line near the bottom of your mrbgem.rake with the two arguments: name and where it comes from.

mrbgem.rake:'hello_world') do |spec|
  spec.license = 'MIT'  = 'Terence Lee'
  spec.summary = 'Hello World'
  spec.bins    = ['hello_world']

  spec.add_dependency 'mruby-print', :core => 'mruby-print'
  spec.add_dependency 'mruby-mtest', :mgem => 'mruby-test'

CLI Architecture

The app is built from two parts a C wrapper in tools/ and a mruby part in mrblib/. The C wrapper is fairly minimal and executes the __main__ method in mruby and instantiates ARGV and passes it to the mruby code. You won't need to touch the C wrapper. The rest of the CLI is written in mruby. You can't have subfolders in mrblib/ but you can have as many files in mrblib/. All these files are precompiled into mruby bytecode The build tool for mruby is written in CRuby (MRI).


By default, mruby-cli generates two kinds of tests: mtest and bintest.


These tests are unit tests, are written in mruby, and go in the test/ directory. It uses the mrbgem mruby-mtest. The available methods to be used can be found here. To run the tests, just execute:

$ docker-compose run mtest


These are integration tests, are written in CRuby (MRI), and go in the bintest/ directory. It tests the status and output of the host binary inside a docker container. To run them just execute:

$ docker-compose run bintest


mruby-cli Development

Compile the mruby-cli binaries

This app is built as a mruby-cli app. To compile the binaries, you must type

docker-compose run compile

and find the binaries in the appropriate directories (mruby/build/<target>/bin/).

The docker container contains the necessary cross toolchain to compile a binary for each supported target. That's why it is checked before running a rake task if it is run inside a container.

Indeed, just using rake compile will not work out of the box because the main build is designed to compile on a 64-bit Linux host. It could work if you are on a 64-Linux host and you have an cross toolchain equivalent to the one we provide into the docker container.

This means that if you want to add a new rake task my_task, you need to add it to the docker-compose.yml to make it available through docker-compose run my_task.

Create the releases

Just type: docker-compose run release

After this command finishes, you'll see the releases for each target in the releases directory.

Create package

We can package the ad hoc release as deb, rpm, msi, or dmg for the following Linux.

To create all the package, just type

docker-compose run package