In this Dockerfile by using the rbenv you have installed the ruby It has also been installed in accordance with phantomjs in this containe
The easiest way to do this is to get from Docker registry
$ docker pull kazu69/ruby:2.3-ubuntu
Also possible to use or from github to get
$ git clone https://github.com/kazu69/docker-ruby.git
$ cd docker-ruby
$ docker build -t kazu69/docker-ruby .
Content type
Image
Digest
Size
324.6 MB
Last updated
about 9 years ago
docker pull kazu69/ruby:2.3-ubuntu