title: Detect Russian characters with grep
body: <p>I'm trying to detect Russian characters with grep, but what I have at the moment does not appear to be doing anything: </p>
  
  <pre><code> echo "Ёё" | grep -Eo "/[А-Яа-яЁё]/u"
  </code></pre>
  
  <p>No output is returned. Is there anything I have to do to tell grep to return the output? </p>