site_list=$(
  perl -e '
    while (<>) {
      if ($ARGV eq "/etc/uucp/Systems") {
        $system{$1} = undef if /^(\w+)/;
        next;
      }
      close ARGV, next unless exists $system{$_};
      $system{$ARGV} = $1, close ARGV if /^Customer Code.*\s(\w+)\s*$/;
    }
    $,=" "; print sort(values %system),"\n";
' /etc/uucp/Systems *)