foreach my $hashref (@$data1) {
  %$hashref = (%$hashref, %$_) for @$data2;
  }

for my $hash1 (@$data1) {
  @{ $hash1 }{ keys %$_ } = values %$_ for @$data2;
  }

foreach my $hash1 (@$data1) {
  for my $hash2 (@$data2) {
    map { $hash1->{$_} = $hash2->{$_} } keys %$hash2;
    }
  }

for my $hash1 (@$data1) {
  for my $hash2 (@$data2) {
    while (my ($k2, $v2) = each %$hash2) {
      $hash1->{$k2} = $v2;
      }
    }
  }