While your suggestion works, it only gives me subkeys for
the first subhash (key1). Can I get the number of all the subkeys?

However, I should've been more code specific in that the key
and subkey names are variables:

%hash = (
  variable_key_name => {
    variable_subkey_name => somevalue,
    another_var_subkey => someothervalue,
    ...
  },
  another_variable_key_name => {
    variable_subkey => somevalue,
    variable_subkey2  => anothervalue,
    ...
  },
  ...
);
[download]

Merci beaucoup!