title: Ansible:Can not define var in Ad-hoc mode
body: <p>I just want to define a var named 'a' with value 'b'
  <a href="https://i.stack.imgur.com/hiSIr.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/hiSIr.png" alt="enter image description here"></a></p>