title: date calculations using unix time
body: <p>Looking for help in unix to get the following date stamps using unix date:</p>
  
  <pre><code>today at 12:00am  
  12:00am - 15 days ago
  12:00am - 30 days ago 
  </code></pre>
  
  <p>in Unix epoch time? (<code>1300295838</code>)</p>