http://qs321.pair.com?node_id=625

Current Perl documentation can be found at perldoc.perl.org.

Here is our local, out-dated (pre-5.6) version:

If you mean how many keys, then all you have to do is take the scalar sense of the keys() function:

    $num_keys = scalar keys %hash;

In void context it just resets the iterator, which is faster for tied hashes.