It might depend on which version of perl you are using, but one way to avoid using a temporary list (%$hash1, %$hash2 is flattened to a list of pairs before being added to the anonymous hash) you can iterate over the hashes using each. 

while (my ($key, $value) = each %$hash1)
{
  $hash3{$key} = $value;
}

[download]
Same for $hash2. This also depends on how the tied hash is implemented but it's worth a try...

Edit: or you could also tie hash3 to fetch data either from hash1 or hash2 ... really depends on what you are trying to achieve and what are your contraints.

In reply to Re: memory use when merging tied hashrefs by Eily
in thread memory use when merging tied hashrefs by Anonymous Monk

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