title: How to convert Unicode string to Unicode escape sequences?
body: <p>I want input a string and output its unicode string, like this "\uXXXX\uXXXX".</p>
  
  <p>Now I already tried two way, but they all output utf-8. How should I do?</p>
  
  <pre class="lang-sh prettyprint-override"><code>printf "文" | hexdump -e '"%X"'
  # 8796E6
  printf "文" | xxd -pu
  # e69687
  </code></pre>