Re^2: Common hash keys

[FunkyMonk]

DB<2> $seen{$_}++ for (keys(%a), keys(%b))
DB<3> x grep { $seen{$_} > 1 } keys(%seen)

You can combine these two into a single statement:

use Data::Dump;

my %a = ( a => 1, b => 2, c => 3 );
my %b = ( b => 2, c => 1, d => 4 );

my %seen;
pp grep { $seen{$_}++ } keys %a, keys %b;

Update: Don't use state variables for this. See lodin's reply

Or, with 5.10

pp grep { state %seen; $seen{$_}++ } keys %a, keys %b;

[lodin]

Be careful with that state. It won't do what (I think) you want.

use 5.010;
sub foo {
  my ($a, $b) = @_;
  sort grep { state %seen; $seen{$_}++ } keys %$a, keys %$b
}

my %a = ( a => 1, b => 2, c => 3 );
my %b = ( b => 2, c => 1, d => 4 );

say join ' ', foo(\%a, \%b);
say join ' ', foo(\%a, \%b);

__END__
b c
a b b c c d

Here you should just stick with my.

lodin