#!/usr/bin/perl -w
use strict;

my @a = (1,2,3);
my @b = (1,2,3,4,5);

my %a_lookup = map {$_,undef} @a;
my @c = grep {! exists $a_lookup{$_}} @b;

print join(',', @c) . "\n";

# __OUTPUT__
# 4,5
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