you have to loop over the keys of both hashes (perldsc has more info), like this:

 for my $first_key ( keys %HoH ) 
 {
     print "$first_key: \n";
     for my $second_key ( keys %{ $HoH{$first_key} } )
     {
         print "$second_key=$HoH{$first_key}{$second_key} ";
     }
     print "\n";
 }
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Update: Fixed typo in second for loop.