title: How to use foreach with a hash reference?
body: <p>I have this code</p>
  
  <pre><code>foreach my $key (keys %ad_grp) {
  
      # Do something
  }
  </code></pre>
  
  <p>which works.</p>
  
  <p>How would the same look like, if I don't have <code>%ad_grp</code>, but a reference, <code>$ad_grp_ref</code>, to the hash?</p>