title: Why cannot embed env vars into curl in Jenkins?
body: <p>In Jenkins pipeline I cannot embed the env variables:</p>
  
  <pre><code>sh 'curl -d '{"color":"green","message":"${BUILD_NUMBER}","notify":false,"message_format":"text"}' -H 'Content-Type: application/json' http:blahbah.com'
  </code></pre>
  
  <p>and the problem is even when I try to use escape chars \ in front of every ' and " the output on the target machine is always
  ${BUILD_NUMBER}</p>
  
  <p>How should look the correct curl syntax here?</p>