This is a minimalistic script to provision of a fresh vagrant box ubuntu/trusty64 for rails development. Uses shell as provisioner and makes use of Brightbox's repository to get a newer version of Ruby the default Ubunutu version of Ruby (currently 1.9.3). Typically people will recommend using a Ruby version management tool like RVM or rbenv, but I wanted the simplest setup to get up and running.
In your Vagrantfile add the below line:
config.vm.provision :shell, path: "./vagrant-rails.sh"
Then the first time you run vagrant up the provisioner script will get triggered and 20 minutes after all the installs have finished you can get developing.
More information on using Shell for Vagrant provisioning: https://docs.vagrantup.com/v2/provisioning/shell.html