#!/usr/bin/env perl
use 5.010; use warnings; use strict;

my %hash = ();    # create empty hash
my $ref = \%hash; # create reference pointing to empty hash

if($ref){
    say 'Reference is true';   # <- always true
} else {
    say 'Reference is false';
}

if (%$ref){ # derefence hash and check the number of elements in it
    say 'Hash has elements';
} else {
    say 'Hash is empty';    # <-- hash has no elements
}

$hash{a} = 1;  # add a key and value to hash

if (%$ref){ # derefence hash and check the number of elements in it
    say 'Hash has elements';    # <-- now it has one key and one value
} else {
    say 'Hash is empty';
}