title: invalid date error in the date command linux
body: <p>In the script I am using the command   </p>
  
  <pre><code>CURRENT_DATE_tmp=`date -d $CURRENT_DATE +%Y%m%d`.
  </code></pre>
  
  <p>It gives error <code>date: invalid date `+%Y%m%d'</code>
  what may be the reason. I know that the variable CURRENT_DATE have value in it.</p>