title: Dockerfile contains a python script that writes to an output file, but the output file is not being created on the container
body: <p>It's my first question, so be gentle :) </p>
  
  <p>I've got a Dockerfile as follows:</p>
  
  <pre><code>FROM centos:latest
  Maintainer Liz Miller
  LABEL description="Image Built with Dockerfile."
  RUN yum -y update
  RUN yum -y install python-setuptools
  RUN easy_install supervisor
  RUN mkdir -p /var/log/supervisor
  RUN yum -y install which
  RUN yum -y install git
  RUN yum install python
  COPY  myscript.py myscript.py
  CMD ["python", "/myscript.py"]
  </code></pre>
  
  <p>And the myscript.py python script is:</p>
  
  <pre><code>text_file = open('output.txt', 'w')
  text_file.write('Hello World')
  text_file.close()
  </code></pre>
  
  <p>When I build the image from this Dockerfile, the image is being built with the script and runs it, I don't see the output.txt. It's just not being created. What is missing? How do I solve this?</p>