Using Docker

Do you want to help with Rouge development but aren't too keen on needing to install Ruby and whatever dependencies are required by Rouge? Docker to the rescue!

Docker can be used as a way install Ruby, Rouge and the development dependencies in a self-contained environment for development. In addition to providing an alternative for users who don't want to install Ruby, it's also a good choice for users with an existing installation of Ruby with which they don't want to interfere.


This guide assumes you have Docker and Git installed.

For a guide on installing Docker, we recommend Docker's official documentation. For a guide on installing Git, take a look at GitHub's documentation.


Downloading Rouge

Clone the project first, and navigate into your clone:

git clone
cd rouge

Configuring the Container

The following line of code sets up Docker with Ruby and Rouge's development dependencies:

docker run -t -v $PWD:/app -v /tmp/vendor:/vendor -w /app -e BUNDLE_PATH=/vendor ruby bundle

Pretty sweet. Let's unpack this:

  • docker run -it: Runs the command in a new container. -t is not strictly necessary but allows nice colors in the output.

  • -v $PWD:app: Maps the current folder into the /app path within the container. Used in conjunction with -w (see below), this allows the container to run as if it were inside this directory.

  • -v /tmp/vendor:/vendor: Maps an arbitrary vendor folder into the /vendor path within the container. This is to persist the installed dependencies across Docker commands, otherwise you would have to re-install each time as containers are ephemeral by nature.

  • -e BUNDLE_PATH=/vendor: Sets an environment variable inside the container that tells Bundler to lookup the dependencies from the /vendor path (that we've mapped to our host machine with the previous line)

  • ruby: Tells Docker which image to use for the container. The ruby image is part of the official library of "base" Docker images.

  • bundle: Runs the bundle command within the container.

Executing Commands

Running Rake

Just replace the bundle command with rake:

docker run -t -v $PWD:/app -v /tmp/vendor:/vendor -w /app -e BUNDLE_PATH=/vendor ruby rake

Running Rack

Similarly, we can run Rack by replacing bundle with rackup:

docker run -t -v $PWD:/app -v /tmp/vendor:/vendor -w /app -e BUNDLE_PATH=/vendor -p 9292:9292 ruby bundle exec rackup --host

The additional command line flags are:

  • -p 9292:9292: Exposes port 9292 of the container to the same port on the host.

  • bundle exec rackup --host Runs Rack and asks it to listen on all addresses. Without this it will only listen on the localhost of the container and we won't be able to access the server from the host machine.

You should be able to visit http://localhost:9292 at this point.


Now that you've got Docker set up, perhaps you'd like to work on a lexer by following our guide.