title: bc truncate floating point number
body: <p>How do I truncate a floating point number using <code>bc</code></p>
  
  <p>e.g if I do </p>
  
  <pre><code>echo '4.2-1.3' | bc
  </code></pre>
  
  <p>which outputs <code>2.9</code> how I get it to truncate/use floor to get <code>2</code></p>