title: $user or $whoami not working in a bash shell script
body: <p>I am learning basic unix shell scripting now. I was trying a code from <a href="http://www.freeos.com/guides/lsst/ch02sec01.html" rel="nofollow noreferrer">here</a> to write my username but it is not working.</p>
  
  <p>The code is:</p>
  
  <pre><code>#
  # Script to print user information who is currently logged in , current date &amp; time
  #
  clear
  echo "Hello $USER"
  echo "Today is \c ";date
  echo "Number of user login : \c" ; who | wc -l
  echo "Calendar"
  cal
  exit 0
  </code></pre>
  
  <p>I tried <code>$whoami</code> instead of <code>$user</code>, but still it is not showing my username. What can be the issue here? I am using vim editor in Ubuntu.</p>