title: Converting lowercase to uppercase in shell script
body: <p>I tried to convert a lowercase string to uppercase and assign it to a variable using the following code</p>
  
  <p><em><strong>The script is written in .tn extension</em></strong> </p>
  
  <pre><code>set y a12
  y_up=$( tr '[A-Z]' '[a-z]' &lt;&lt;&lt; $y)
  echo $y
  echo $y_up
  </code></pre>
  
  <p>But I am getting the error </p>
  
  <pre><code>invalid command name "A-Z"
  while executing
  "A-Z"
  invoked from within
  "y_up=$( tr '[A-Z]' '[a-z]' &lt;&lt;&lt; $y) "
  </code></pre>
  
  <p>How can I convert this?</p>