title: perl + identify if param is empty value from ARG
body: <p>when I run the following script.pl script with no arguments:</p>
  
  <pre><code>./script.pl
  </code></pre>
  
  <p>I do not get the message <code>No arg</code>. Why? How to identify if <code>$param</code> is a null value or empty value, same as <code>[ -z</code> from ksh?</p>
  
  <pre><code>#!/usr/bin/perl
  my $param = $ARGV[0];
  if ($param = "") {
      print No arg;
  } else {
      print arg: $param;
  }
  </code></pre>