I don't think the question is actually about how to facilitate the transfer, but more about how to implement the "decoding".

acron5, you should probably investigate the use of regular expressions (s/blah/foo/) or translation operator (tr/1-9/a-i/). The look at looping to see how one can iterate over the contents of an entire file. Then if you read closely about regular expressions and reading data from a file you will realize that you don't need to iterate and can do it all with one regular expression or translation.