vagrant docker-run and env variables

Commands

#confirms env variable is set in container
vagrant docker-run -- sh -c 'exec env | grep DB_PORT_5432_TCP_PORT'

#can't echo env variable because evaluated on VM host
vagrant docker-run -- sh -c 'echo $DB_PORT_5432_TCP_PORT'

#can't connect to psql because of that
vagrant docker-run db -- sh -c 'exec psql -h $DB_PORT_5432_TCP_ADDR -p $DB_PORT_5432_TCP_PORT -U postgres'

Vagrantfile

Vagrant.configure("2") do |config|
  config.vm.define "db" do |db|
    db.vm.provider "docker" do |d|
      d.image = "library/postgres"
      d.link 'db:db'
    end
  end
end