title: Appending to PATH in a Windows Docker container
body: <p>I need to append to the PATH within a Windows Docker container, and I've tried many permutations.</p>
  
  <pre><code>ENV PATH=%PATH%;C:\\Foo\\bin
  ENV PATH=$PATH;C:\\Foo\\bin
  ENV PATH="%PATH%;C:\Foo\bin"
  ENV PATH="$PATH;C:\Foo\bin"
  RUN "set PATH=%PATH%;C:\Foo\bin"
  </code></pre>
  
  <p>None of these work: they don't evaluate the preexisting PATH variable.</p>
  
  <p>What is the right syntax to append to the PATH? Can I even append to the PATH inside Docker? (I can on similar Linux containers)</p>