in reply to Generate union of the two hashes

As the thing you want to output is a hash ref, the statement print $h3 will output something like HASH(0x182f384). You will get something closer to your expected output by using Data::Dumper, swapping your print statement for use Data::Dumper; print Dumper $h3;. See How can I visualize my complex data structure? for more information.

The reason you are clobbering your initial hash is because your structure is a hash of hashes, so while they are different at the base level, you have the same object (a hash reference) associated with the key drug comparison. To make a shallow copy, I usually use Data::Dumper again, this time in an eval in a do: 

my $h1 = {
    'drug comparison' => 
    {
          '7003000.xml' => {
                             'entity' => 'a1, a2, a3'
                           },
          '70037559.xml' => {
                              'entity' => 'x1, x2, x3'
                            }
        }
};
my $copy = do{my $VAR1; eval Dumper $h1; $VAR1;};

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I would suggest making the copy in your union_of_h1_h2 sub.

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Re^2: Generate union of the two hashes
by shan_emails (Beadle) on Sep 08, 2010 at 15:19 UTC
    Hi All,

    Thanks for all your answers.

    now i used "Clone" module. so the address of the copying hash has been changed. so now the changes affected only in h3 hash.

    use Clone qw(clone);

$h1 = {
    'drug comparison' => 
    {
          '7003000.xml' => {
                             'entity' => 'a1, a2, a3'
                           },
          '70037559.xml' => {
                              'entity' => 'x1, x2, x3'
                            }
        }
};

$h2 = {
    'drug comparison' => 
    {
          '7004562.xml' => {
                             'entity' => 'z1, z2, z3'
                           },
          '70037559.xml' => {
                              'entity' => 'e1, e2, e3'
                            }
        }
};

$h3 = union_of_h1_h2 ($h1, $h2);
print $h3;


sub union_of_h1_h2 {
    my ($ai, $ref) = @_;
    my $output = clone($ai);
        
    foreach my $_ref (keys %$ref) {
        unless (exists $output->{$_ref}) {
            $output->{$_ref} = $ref->{$_ref};
        }else {
            foreach my $filename (keys %{$ref->{$_ref}}) {
                if (!exists $output->{$_ref}->{$filename}) {
                    $output->{$_ref}->{$filename} = $ref->{$_ref}->{$f
+ilename};
                }
            }
        }
    }
    return $output;
}

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    Wishes
    Shanmugam A.
[reply]
[d/l]

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