You can probably determine this from one of the environment variables stored in %ENV. For example, apache stores it in $ENV{'SERVER_PORT'}

Use this script to print the environment of a CGI request:

use strict;
use CGI qw(:standard);

print header, start_html;

for my $k (sort keys %ENV) {
  print "$k = $ENV{$k}<br>";
}

print end_html;
[download]

HTH, HAND.