Be aware that if the two smaller hashes contain the same key, then the value that ends up in the composite hash will depend upon the order you list the smaller hashes in the composing statement:

@val=({23=>1, 43=>1, 34=>1, 66=>1, 99=>1},{33=>1, 64=>1, 35=>1, 54=>1,
+ 78=>1});;

pp \@val;;
[
  { 23 => 1, 34 => 1, 43 => 1, 66 => 1, 99 => 1 },
  { 33 => 1, 35 => 1, 54 => 1, 64 => 1, 78 => 1 },
]


$val[2] = { %{ $val[0] }, %{ $val[ 1 ] } };;

pp \@val;;
[
  { 23 => 1, 34 => 1, 43 => 1, 66 => 1, 99 => 1 },
  { 33 => 1, 35 => 1, 54 => 1, 64 => 1, 78 => 1 },
  { 23 => 1, 33 => 1, 34 => 1, 35 => 1, 43 => 1, 54 => 1, 64 => 1, 66 
+=> 1, 78 => 1, 99 => 1 },
]
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