for my $i(0..$#list1){
   $list1[$i] += $list2[$i];
}

##</code><code>##

my @list2;
push @list2, $some_value, $some_other_value, $this_variable, $that_variable;
for my $i(0..$#list1){
   $list1[$i] += $list2[$i];
}