my @GOODLIST = qw(10.0.1.5 10.0.2.1);
use CGI qw(:all); use strict;
for my $remote_addr (remote_addr()) {
  if (grep $remote_addr, @GOODLIST) {
    print redirect ("/secret/URL/here/foo.thingy");
  } else {
    print header ( status => 404 ),
      start_html( 'error' ),
      "The resource you tried to access is not found",
      end_html;
  }
}