$c=join':',qw/42 t 83 s 0 65 78 n s 72 d 82 0 O d 82 k 0 g
65 67 j 69 82 1 ;""tnirp/;

while($c)
{
  $d=@{[split//,$n]};

  # Two different logic branches, depending upon the length 
  # of $n (the result), which starts as length 0
  if ($d<8)
    # Pop characters off the end (in reverse order) and
    # place onto $n
    { $n .= chop $c ; }
  else
    # read $c from the beginning, adding ASCII 32 to numbers
    # or shifting up one letter for non-numbers and place
    # onto $b
    { $b .= ($e=${[split/:/,$c]}[0]) =~ /^\d+/ ? chr $e+32:  
                                                 ++$e; }

  # If $b is non-NULL (ie, we have parsed the last eight 
  # characters off of $c into $n) Shift off the first number 
  # or character from $c, otherwise don't touch it
  $c = ($b && $c =~ /(\d+|\w):(.*)$/x)  ? $2         : $c;

  # If $c is NULL (ie, we've processed the input string),
  # wedge $b plus an OS-specific linefeed between the
  # quotes, otherwise leave $n alone
  $n = (!$c && $n =~ /(.+")(".)/)      ? $1.$b.$/.$2 : $n
}
eval $n