Hi try this with set::Scalar module,

use Set::Scalar;

@a = (1, 2, 3, 4, 5, 6);
@b = ( 3, 4 , 5, 6, 7, 8);

$a = Set::Scalar->new(@a); 
$b = Set::Scalar->new(@b); 
print $b->difference($a);
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o/p: (7 8)

Regards,
Gubendran.L