try:

#!/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 "$_ -> ", convert($_);
  }
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prints:

abcd -> 00011011
dcba -> 11100100
abab -> 00010001
cdcd -> 10111011
abba -> 00010100
caab -> 10000001
[download]