map could also be used to generate the sums of the intersection set of the two hashes (with no exceptions thrown): 

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 }

[download]
The exists test could be moved into a separate grep step for perhaps greater clarity, but I'd expect a bit of a performance hit with large hashes.

BTW: Won't
    my %h3 = map {$_ => $h1{$_} + $h2{$_}} keys %h1, keys %h2;
cause "Use of uninitialized value ..." warnings unless that warning is disabled?

Give a man a fish:  <%-{-{-{-<

In reply to Re^2: merge two hashes into one by AnomalousMonk
in thread merge two hashes into one by ovedpo15

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