c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"my %h1 = qw(a 1  b 2  c 3     );
 my %h2 = qw(     b 7  c 8  d 4);
 ;;
 my %h_out =
   map  exists $h2{$_} ? ($_ => $h1{$_} + $h2{$_}) : (),
   keys %h1
   ;
 dd \%h_out;
"
{ b => 9, c => 11 }