my $one = 1;
my $two = 2;
my $three = 3;
my @arr = ($one, $two, $three);
$arr[0] += 10;
print "\$one = $one\n"; # still 1
for my $x ($one, $two, $three) {
  $x += 0.5;
}
print "\$one = $one\n"; # changed to 1.5
for my $x (@arr) {
  $x += 0.1;
}
print "\$one = $one\n"; # still 1.5, no link between $arr[0] and $one