title: Less: add a number to string
body: <p>I need to extract part of a string and add a number to it. Here is my code:</p>
  
  <pre><code>.sprite-position-offset(@sprite; @offset-x; @offset-y) {
    @sprite-offset-x: ~`"@{sprite}".split(', ')[2]` + @offset-x;
    @sprite-offset-y: ~`"@{sprite}".split(', ')[3]` + @offset-y;
    background-position: @sprite-offset-x  @sprite-offset-y;
  }
  </code></pre>
  
  <p>The result of</p>
  
  <pre><code>~`"@{sprite}".split(', ')[2]`
  </code></pre>
  
  <p>is <code>100px</code>, for example.</p>
  
  <p>In the example above i get <code>Unrecognised input in file</code> error.</p>
  
  <p>How can I achieve this?</p>