title: pack('C4", $digits) in perl
body: <p>In Writing CGI Applications with Perl, have following code to log visitors.</p>
  
  <pre><code>(my $digits = #ENV{'REMOTE_ADDR'}) =~ s/\.//g;
  my $address = pack("C4", $digits);
  </code></pre>
  
  <p>in perldoc, </p>
  
  <blockquote>
    <p>pack TEMPLATE,LIST</p>
  </blockquote>
  
  <p>"C4" should be the template. What's the actual meaning of this?</p>