#!/usr/bin/perl -l

# http://perlmonks.org/?node_id=1181779

use strict;
use warnings;

sub convert
  {
  unpack('H*', shift() =~ tr/cd/qr/r) =~ tr/1267/0101/r;
  }

for ( qw( abcd dcba abab cdcd abba caab ) )
  {
  print "$_ -> ", convert($_);
  }