use File::Copy qw(move);
use Text::CSV;

use strict;
use warnings;
use autodie; # no need to catch open/read/write/close errors anymore

my $csv = Text::CSV->new ({ binary => 1, auto_diag => 1, eol => "\n" });

my $oldfile = "old.csv";
my $newfile = $oldfile . ".tmp";

open my $in,  "<", $oldfile;
open my $out, ">", $newfile;

while (my $row = $csv->getline ($in)) {
    splice @$row, 1, 0, "New Col 2";
    $csv->print ($out, $row);
    }

close $in;
close $out;