#!/usr/bin/perl 
use strict;
use warnings;
use Data::Dumper;
use List::Compare;

my $a = '1,2,3,6,7,9,1,-7,2,6';
my $b = '7,6,7,9,12,-22,-3';
my @a = split ',', $a; 
my @b = split ',', $b; 

my $lc = List::Compare->new( \@a, \@b );

my @intersection = $lc->get_intersection;

print Dumper(@intersection);
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output :

$VAR1 = '6';
$VAR2 = '7';
$VAR3 = '9';
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voilą ;)
PooLPi