title: How to check if a variable is empty in tcl
body: <p>How do you ceck if a variable is empty ? It could contain a <code>"\n"</code> or spaces. 
  I am currently doing this</p>
  
  <pre><code>if {{string trimleft $var} != ""} {
     # the variable is not empty
     puts $var
   }
  </code></pre>
  
  <p>However the variable printed still seems to be empty ?  will <code>trimleft</code> remove <code>"\n"</code> ?
  Is there a  better approach to check if a string is empty ?</p>