Just add a few lines:

my @totals;
foreach my $row ( 1 .. 10 ) {
    my @output;
    foreach my $column ( 1 .. 10 ) {
        push @output , $column;
    }
    $totals [$_] += $output [$_] for 0 .. $#output;
    print join ',' , @output;
}
# print column totals here
print "@totals";
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This will even work if the rows don't all have the same size.

Abigail