Thanks so much for the help on the if/then/else statement, I was over thinking how to approach the problem.

 
my $hash = $hash_name eq 'dat'
   ? \%dat_mapping
   : \%eng_mapping;
for my $file_name (keys %$hash) {
[download]

Works great, I did not realize you could put a hash ref in a scaler, so this was something new to me also. Tks again.