For the unnested case this code can determine the joined set of keys of two hash references given the keys of the two hash references separately: 
use Data::Dumper;

my $hash1 = {
    common_key => 'foo',
    hash1_specific_key => 'some value'
};

my $hash2 = {
    common_key => 'bar',
    hash2_specific_key => 'some other value'
};

my $joined_keys = [ keys( %{ {
    map { $_=>undef }  keys( %{$hash1} ) , keys( %{$hash2} ) 
} } ) ];

print Data::Dumper->Dump([$joined_keys],['joined keys']);

[download]
Outputs: 
$joined keys = [
                 'hash2_specific_key',
                 'common_key',
                 'hash1_specific_key'
               ];

[download]

In reply to Re^2: What is the easiest way to merge two hashes? by tkguifan
in thread What is the easiest way to merge two hashes? by tkguifan

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