%key = sort keys %key;

##</code><code>##

%key = (
    foo   => 'bar',
    bazz  => 'bump',
    ping  => 'pong',
    putt  => 'pop',
);

##</code><code>##

%key = (
    foo  => 'bazz',
    ping => 'putt',
);

##</code><code>##

%key = (
    foo   => 'bar',
    bazz  => 'bump',
    ping  => 'pong',
    putt  => 'pop',
);

my @keys = keys %key; # foo, bazz, ping, putt

%key = @keys; foo => bazz, ping => putt