title: Surround a string with markers
body: <p>I have a text file and need to surround some words with a desired string pair.</p>
  
  <p>For example, i have a following file:</p>
  
  <pre><code>abc def
  gefhi jkl
  </code></pre>
  
  <p>and want to surround all the occurrences of <code>ef</code> with <code>ab</code> and <code>xy</code>, so the result will be following:</p>
  
  <pre><code>abc dabefxy
  gabefxyhi jkl
  </code></pre>
  
  <p>How can i do this?</p>