title: subtract days from a date in bash
body: <p>I want to subtract "number of days" from a date in bash. I am trying something like this ..</p>
  
  <pre><code>echo $dataset_date #output is 2013-08-07
  
  echo $date_diff #output is 2   
  
  p_dataset_date=`$dataset_date --date="-$date_diff days" +%Y-%m-%d` # Getting Error
  </code></pre>