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

use strict;
use warnings;

my $csv = Text::CSV->new({binary => 1, eol => "\n"})
	or die "Cannot use CSV: ".Text::CSV->error_diag ();

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

open my $in, $oldfile or die "$oldfile: $!";
open my $out, '>', $newfile or die "$newfile: $!";

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

close $in;
close $out;

move($newfile, $oldfile) or die "Can't move: $!";