title: assign variable by bash script during variable declaration time
body: <p>For my <strong>azure-pipeline.yml</strong> file, I would like to assign variable by bash script to get the name after the slash from the repoName as my imageName </p>
  
  <pre><code>variables:
    vmImageName: 'ubuntu-18.04'
    repoName: $(Build.Repository.Name)
    imageName: ${repoName##*/}
  </code></pre>
  
  <p>The <strong>repoName</strong> is <code>top/cci</code> I expected the print out result for <strong>imageName</strong> is <code>cci</code>. But the result is ${top/cci##*/}</p>
  
  <p>How can I use the bash script to get the strings after the slash during the variable assignment? </p>