title: Run a command line when starting a docker container
body: <p>As far as I'm concerned you can run a command line when building an image with <code>RUN</code> or when running a container with <code>CMD</code>. Is there anyway to do so when starting a docker container?</p>
  <p>My goal is to run the gcloud datastore automatically just after typing <code>docker start my_container_name</code>.</p>
  <p>If this is possible, which changes should I apply to my Dockerfile?</p>
  <p>(I have already installed all the packages required and I can run that command after <code>docker run --name my_container_name -i -t my_image_name</code> but I want it to be run also when starting the container)</p>