title: Dockerfile - Defining an ENV variable with a dynamic value
body: <p>I want to update the PATH environment variable with a dynamic value. This is what I've tried so far in my Dockerfile:</p>
  
  <pre><code>...
  ENV PATH '$(dirname $(find /opt -name "ruby" | grep -i bin)):$PATH'
  ...
  </code></pre>
  
  <p>But export shows that the command was not interpreted:</p>
  
  <pre><code>root@97287b22c251:/# export
  declare -x PATH="\$(dirname \$(find /opt -name \"ruby\" | grep -i bin)):\$PATH"
  </code></pre>
  
  <p>I don't want to hardcode the value. Is it possible to achieve it?</p>
  
  <p>Thanks</p>