title: Adding a binary to the PATH from a Docker GitHub Action for use by later workflow steps
body: <p>I am trying to create a Dockerfile based action that adds a program to the <code>$PATH</code> so that it can be used by later actions. My action runs code like this:</p>
  
  <pre class="lang-sh prettyprint-override"><code>mkdir -p $GITHUB_WORKSPACE/bin
  echo "echo Hello, world!" &gt; $GITHUB_WORKSPACE/bin/hello-world
  echo "::add-path::$GITHUB_WORKSPACE/bin"
  </code></pre>
  
  <p>My test workflow uses this like so:</p>
  
  <pre><code>jobs:
    test:
      runs-on: ubuntu-latest
      steps:
        - uses: actions/checkout@v1.0.0
        - name: Add program to path
          uses: ./
        - name: Use program
          run: hello-world
  </code></pre>
  
  <p>This fails because while the program has been added to <code>$GITHUB_WORKSPACE/bin/hello-world</code> the value of <code>$GITHUB_WORKSPACE</code> is different in the action and in the workspace step.</p>
  
  <p>In the action it is <code>/github/workspace/</code>, while in the workflow it is <code>/home/runner/work/setup-gleam/setup-gleam/</code>, so the <code>$PATH</code> addition set by the action is not correct.</p>
  
  <p>How can I add a file to a directory from a dockerfile based GitHub action so that it is on the path for the rest of the workflow? It seems that there is no writable <code>$PATH</code> directory shared between dockerfile actions and non-dockerfile actions.</p>