# declare anonymous hash
my $hash = {};

map { $hash->{$_->[0]} = ['',$_->[1]] } @foo;

for my $key (@bar)
{
  $hash->{$key->[0]} ? $hash->{$key->[0]}[0] = $key->[1]
                     :  $hash->{$key->[0]} = [$key->[1],''];
}