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: $!";
[download]

I don't know who gave you that advice, but version 0.23 is almost 10 years old and full of bugs (by modern standards). If you want to study the current state of CSV parsing, you should look at Text::CSV_XS and Text::CSV. Both have other maintainers than 10 years ago, and both do now mostly what the community expects it to do and more. The XS version is way faster than the pure-perl version, but it is save to always use Text::CSV, as that will use Text::CSV_XS under the hood if it is installed.

wind's paste is fine. I would make small changes to include the relative new auto_diag to catch all errors:

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;
[download]

I am having a bit of trouble with this because it seems to be putting quotes around some of the column values. Using an example tab limited file with 4 lines, the final column on every row apart from the last one is put in quotes

Also using this code

splice @$row, 1, 0, "New Col 2";
[download]

the new column text is in quotes which I don't want.

thank-you

You obviously did not take the time to read the exhaustive documentation the comes with Text::CSV_XS. By default, fields with spaces are quoted. There is an option (attribute) available to do the opposite:

       quote_space
           By default, a space in a field would trigger quotation. As 
+no rule
           exists this to be forced in CSV, nor any for the opposite, 
+the
           default is true for safety. You can exclude the space from 
+this
           trigger by setting this attribute to 0.
[download]


Enjoy, Have FUN! H.Merijn

Good, because modifying an existing one is simply

1. create a new one
2. rename new one to name of old one