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%dest = ();

...
            another_key => 2 );

%names = ( 1 => 'name1', 2 => 'name2' );

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$dest{name} = $names{ $source{very_long_key_name} };

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$dest{name} = exists $source{very_long_key_name} ?
              $names{ $source{very_long_key_name} } :
              '';

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$dest{name} = not exists $source{very_long_key_name} ? '' :
              $names{ $source{very_long_key_name} };

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print "name code = $source{very_long_key_name}\n";            # 1
print "converted = $names{ $source{very_long_key_name} }\n";  # name1
print "dest name = $dest{name}\n";                            # 1

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$dest{'name'} = (! (exists($source{'very_long_key_name'}) ? '' :
                   $names{$source{'very_long_key_name'}}        ) );

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$dest{name} = (not exists $source{very_long_key_name}) ? '' :
              $names{ $source{very_long_key_name} };

print $dest{name}; # name1