# $hash{$key} = { field1 => 'value', ... };

my @keys = keys %{$hash{(keys %hash)[0]}};
my $format = "%10s " . ("%10s " x @keys) . "\n";
printf $format, "Key", @keys;

foreach my $key (keys %hash) {
   printf $format, $key, @{$hash{$key}}{@keys};
}