my $csv = Text::CSV_XS->new ({ binary => 1, auto_diag => 1, sep_char => $separator});
while (my $row = $csv->getline ($fh)) {
    $row->[-1] =~ m/^\s*([0-9]+)\s*\z/ or
        warn "Last field of row ", $csv->record_number, " is not numeric: '$row->[-1]'\n";
    }