It has been pointed out to me that I should have used <strike> instead of simply deleting the code I originally posted.

My original solution calculated the sum of the column items in each row rather than the sum of each column. The comment was that even though this didn't answer the OP's question it was nonetheless interesting code that others might like to see.

So, rather than doing any more (possibly confusing) updates to my last post, I've posted my original offering separately here.

#!perl

use 5.12.0;
use warnings;

use List::Util qw{sum};

my $total = 0;

while (<DATA>) {
    $total += sum split;
}

say $total;

__DATA__
1 2 3 4 5 6
1 2 3 4 5 6
[download]

Outputs:

$ row_sum.pl
42
[download]

Enjoy!