When you call or return from a Perl subroutine, your argument list gets flattened into a simple list. For your argument list as presented, this means that the first three elements of your argument list are assigned to $self, $copyLocation, and $tcid and the remaining elements of the argument list are assigned to %parseData. If you want to pass multiple arrays or hashes, you need to use Pass by Reference. See perlreftut for more info on references and perlsub for more info on Perl subroutines.