title: Command `source` doesn't work in Dockerfile
body: <p>I want build my images, here is my Dockerfile:</p>
  
  <pre><code>FROM ubuntu:16.04
  
  MAINTAINER 'hulei886@aliyun.com'
  
  ENV PHANTOMJS_VERSION 2.1.1 
  ENV PYTHON_VERSION 3.6.3
  
  # install python3.6.3
  RUN apt-get update \
   &amp;&amp; apt-get install -y build-essential \
                         git \
                         curl \
                         libssl-dev \ 
                         zlib1g-dev \
                         libncurses5-dev \
                         libncursesw5-dev \
                         libreadline-dev \
                         libsqlite3-dev \
  
   &amp;&amp; apt-get install -y libgdbm-dev \
                         libdb5.3-dev \
                         libbz2-dev \
                         libexpat1-dev \
                         liblzma-dev \ 
                         tk-dev \
  
   &amp;&amp; cd ~ \
  
   &amp;&amp; git clone https://github.com/pyenv/pyenv.git .pyenv \
   &amp;&amp; echo 'export PYENV_ROOT="$HOME/.pyenv"' &gt;&gt; ~/.bashrc \
   &amp;&amp; echo 'export PATH="$PYENV_ROOT/bin:$PATH"' &gt;&gt; ~/.bashrc \
   &amp;&amp; echo 'eval "$(pyenv init -)"' &gt;&gt; ~/.bashrc \
   &amp;&amp; source ~/.bashrc \
  
   &amp;&amp; curl -L https://raw.githubusercontent.com/yyuu/pyenv- installer/master/bin/pyenv-installer | bash \
  
   &amp;&amp; pyenv install PYTHON_VERSION \
  
   &amp;&amp; pyenv global PYTHON_VERSION \
   &amp;&amp; cd .. \
   CMD [python]
  </code></pre>
  
  <p>but when i run "docker build . -t [mytag]"，
  git clone command didn't clone anything,here is screenshot:
  <a href="https://i.stack.imgur.com/pqPgH.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/pqPgH.png" alt="enter image description here"></a></p>
  
  <p>I need help to fix this problem,thanks！</p>