Initialise the new hash with one of the old ones, so you can only iterate over the other one: 
#!/usr/bin/perl
use warnings;
use strict;

my %hash1 = (a => 12, b => 15);
my %hash2 = (a => 30, c => 17);

my %merged = %hash1;
$merged{$_} += $hash2{$_} for keys %hash2;

use Data::Dumper;
print Dumper \%merged;

[download]
($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

[download]

In reply to Re: merge two hashes into one by choroba
in thread merge two hashes into one by ovedpo15

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