use warnings;
use strict;
use Data::Dump qw(dd pp);

my %hash =
(
    a => 11,
    b => 12,
    c => 13,
    d => 14,
);

while (my ($key, $value) = each %hash)
{
    print "key is $key, value is $value, hash is ", pp(\%hash), "\n";
    delete $hash{$_} for qw( a b c d );
    $hash{x} .= $key;
}

dd \%hash;