How to clear a Perl hash

Let's say we define an anonymous hash like this:

my $hash = {};

And then use the hash afterwards. Then it's time to empty or clear the hash for reuse. After some Google searching, I found:

%{$hash} = () 

and:

undef %{$hash}

Both will serve my needs. What's the difference between the two? Are they both identical ways to empty a hash?

%$hash_ref = (); makes more sense than undef-ing the hash. Undef-ing the hash says that you're done with the hash. Assigning an empty list says you just want an empty hash.

Yes, they are absolutely identical. Both remove any existing keys and values from the table and sets the hash to the empty list.

See perldoc -f undef:

undef EXPR
undef   Undefines the value of EXPR, which must be an lvalue. Use only on a scalar value, an array (using "@"), a hash (using "%"), a subroutine (using "&"), or a typeglob (using "*")...
Examples:

               undef $foo;  
               undef $bar{'blurfl'};      # Compare to: delete $bar{'blurfl'};  
               undef @ary;  
               undef %hash;

However, you should not use undef to remove the value of anything except a scalar. For other variable types, set it to the "empty" version of that type -- e.g. for arrays or hashes, @foo = (); %bar = ();