title: Jenkins export build number to file
body: <p>I'm using the Export parameters plugin.
  I want to export the build number to a file.</p>
  
  <p>I'm using string parameter:</p>
  
  <pre><code>jenkins-build
  ${BUILD_NUMBER}
  </code></pre>
  
  <p>Export to properties file using key:</p>
  
  <pre><code>jenkins-build
  </code></pre>
  
  <p>But the exported file does not update the build number. I get:</p>
  
  <pre><code>jenkins-build=${BUILD_NUMBER}
  </code></pre>
  
  <p>Do I need to do something else?</p>