When using Docker Machine on OS X, there's an incantation that needs to be run in every shell where you want to run Docker. Direnv can help mitigate that annoyance:

Add to ~/.config/direnv/direnvrc

use_docker-machine(){
  local env=${1:-default}
  echo Docker machine: $env
  local machine_cmd=$(docker-machine env --shell bash $env)

  eval $(docker-machine env --shell bash $env)
}

Any project that's using docker, add to .envrc:

use docker-machine

One nice feature to this is that you can have different Docker machine VMs per project, if needed by saying use docker-machine special, for instance.

Note that when using this pattern, when docker-machine warns you to eval (docker-machine env), you'll want instead to direnv reload.