print "'hash{key}' is a hash reference\n" if ref(\%{$hash{key}}) eq 'HASH';

##</code><code>##

#!/usr/local/bin/perl5.6.0
use strict;
use warnings;

my $hash =
{
    h1  => { ss1 => 'Howdy' },
    h2  =>
    {
        hh1 => { sss1    => 'Hello' }
    },
    s1 => 'Doody',
    a1  => [],
};

dig( $hash );

sub dig
{
    my ( $hole ) = @_;

    if( ref($hole) eq 'HASH' )
    {
        foreach my $l ( keys %{$_[0]} )
        {
            dig( $_[0]->{$l} );
        }
    }
    elsif ( ref($hole) eq 'ARRAY' )
    {
        print q{What do I do with an Array ref?\n};
    }
    else
    {
        my $leaf = $hole; # leaf in a hole?!?

        print qq{Found a leaf in an hole! [$leaf]\n};
    }
}