Here are two techniques (from the Perl Cookbook) that might point you in the right direction.

use warnings;
use strict;

my %hash_a = (
    one   => 'a1',
    two   => 'a2',
    three => 'a3',
    five  => 'a5',
);

my %hash_b = (
    one   => 'b1',
    two   => 'b2',
    three => 'b3',
    four  => 'b4',
);

suba ();
subb ();

sub suba {
    my ( @common, @uncommon ) = ( (), () );

    foreach ( keys %hash_a ) {
        push @common,   $_ if     exists $hash_b{$_};
        push @uncommon, $_ if not exists $hash_b{$_};
    }
    foreach ( keys %hash_b ) {
        push @uncommon, $_ if not exists $hash_a{$_};
    }

    print "in both: @common\n not in both: @uncommon\n\n";
}

sub subb {
    my @common     = grep {     exists $hash_b{$_} } keys %hash_a;
    my @uncommon   = grep { not exists $hash_b{$_} } keys %hash_a;
    push @uncommon, (grep { not exists $hash_a{$_} } keys %hash_b);
    print "in both: @common\n not in both: @uncommon\n\n";
}
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The output is:

in both: three one two
not in both: five four

in both: three one two
not in both: five four