# suppose @myvec is an array of integers.
my $sum = 0;
for (my $i = 0; $i < scalar(@myvec); $i++)
{
    $sum += 2 * $myvec[$i];
}

##</code><code>##

my $sum = 0;
foreach my $i (@myvec)
{
    $sum += 2 * $i;
}

##</code><code>##

my $sum = 0;
$sum += 2 * $_ foreach @myvec;

##</code><code>##

$sum = eval join('+', map { 2 * $_ } @myvec);