use strict;
use warnings;
use Data::Dumper;

my @list1 = qw(a b c);
my @list2 = qw(d e f);

changem(\@list1, \@list2);

print "\n=== After changem ===\n";
printf "%s\n", join q(, ), @list1;
printf "%s\n", join q(, ), @list2;

sub changem {
    my $aref1 = shift or die "no list1";
    my $aref2 = shift or die "no list2";

    $aref1->[1] = 'Camel';
    $aref2->[1] = 'LLama';

    print "list1: " . Dumper($aref1);
    print "list2: " . Dumper($aref2);
}