title: how do I build a docker image without existing from a docker file
body: <p>new to dockers. </p>
  
  <p>running this <code>docker build .</code></p>
  
  <p>this is the <code>Dockerfile</code></p>
  
  <pre><code>FROM gcr.io/google_appengine/python
  
  # Create a virtualenv for dependencies. This isolates these packages from
  # system-level packages.
  RUN virtualenv /env
  
  # Setting these environment variables are the same as running
  # source /env/bin/activate.
  ENV VIRTUAL_ENV /env
  ENV PATH /env/bin:$PATH
  
  # Copy the application's requirements.txt and run pip to install all
  # dependencies into the virtualenv.
  #ADD requirements.txt /app/requirements.txt
  #RUN pip install -r /app/requirements.txt
  
  # Add the application source code.
  ADD . /app
  
  # Run a WSGI server to serve the application. gunicorn must be declared as
  # a dependency in requirements.txt.
  CMD gunicorn -b :$PORT main:app
  
  CMD bash1  "while true; do echo hello; sleep 1;done"
  
  CMD ["sh", "while true; do echo hello; sleep 1;done"]
  CMD "echo" "Hello docker!"
  </code></pre>
  
  <p>but after, when I run <code>docker ps</code> I don't see the image. </p>