title: How to check if a string is empty
body: <p>I need to check if a string (user input on an entry box) is empty or not and do some action based on that condition once I push the "Play" button.
  This is my script:</p>
  
  <pre><code>entry .eInput -width 50 -relief sunken -justify center -textvariable Input
  button .bAction  -text "Play" -width 30 -height 5 -activebackground green -font "-12" 
  
  bind .bAction &lt;1&gt; {
   if {$Input ne ""}
    { puts "string is not empty"}
   else { puts "string is empty"}
                    }
  </code></pre>
  
  <p>But when I push the "Play" button this is the error:</p>
  
  <pre><code>wrong # args: no script following "$Input ne """ argument
  wrong # args: no script following "$Input ne """ argument
      while executing
  "if {$Input ne ""}"
      (command bound to event)
  </code></pre>
  
  <p>Any idea on how to fix it?</p>