my @ary1 = qw/1 2 3 4 5 4 6/;
my @ary2 = qw/5 6 7 8 7 9 10/;
my %h;
$h{$_} .= "a" for ( @ary1 );
$h{$_} .= "b" for ( @ary2 );
compare( "Only in ary1", "a\$", \%h );
compare( "Only in ary2", "^b", \%h );
compare( "Common to both", "ab", \%h );

sub compare {
    my ( $text, $regex, $hash ) = @_;
    print join "\n", $text, grep { $$hash{$_} =~ /$regex/ } keys %$hash;
    print "\n";
}