#!/usr/local/bin/perl
use strict;
use warnings;
my %hash;
my @array_keys;
my @keys = qw(xx yy zz);
@hash{@keys}=([{'key1'=>1}],[{'key2'=>2}],[{'key3'=>3}]); #hash slice
@array_keys = keys %hash;
print "@array_keys\n";

push @{$hash{'aa'}},{'key4'=>4};  #add another key
@array_keys = keys %hash;         #update the array
print "@array_keys\n";