How about a HoA structure?

foreach (@lines)
{
  my ($key, $value) = munge($_);
  next unless defined $value;  # Don't bother creating empty hash entr
+ies in the first place ;)
  push @{$hash{$key}}, $value;
}
[download]

That way, you'll end up with an array of mac addresses under the key "MACADDRESS". (And same with any other data that gets repeated)