Hi, the most interesting thing you may be missing all data you get from Text::CSV using $row = $csv->getline( $fh ) statement is an array refence and the following statement push @rows, $row; puts this array reference to an array so you end with a data structure called array of array (AoA). You can change the data while it gets parsed as shown in the docs of the Text::CSV or later when it's inside of AoA @rows. Here is a sample script for change data while it's read:

# ..\perl.exe
# perlmonks http://perlmonks.org/index.pl?node_id=951536
# Text::CSV witer

use strict;
use warnings;


use Text::CSV;

my $input_file = "951536_in.csv";
my $output_file = "951536_out.csv";

 my @rows;
 my $csv = Text::CSV->new ( { binary => 1 } )  # should set binary att
+ribute.
                 or die "Cannot use CSV: ".Text::CSV->error_diag ();


#read file 
 open my $fh, "<:encoding(utf8)", $input_file or die "$input_file: $!"
+;
 while ( my $row = $csv->getline( $fh )) {
     $row->[0] =~ s/^(.*)(\d+)$/abc$2/; # replace leading chars
     $row->[1] =~ s/^(.*)(\d+)$/$1asd$2/; # insert between char and di
+git
     $row->[2] =~ s/^(.*)(\d+)$/$1xyz/; # replace digits
     push @rows, $row;
 }
 $csv->eof or $csv->error_diag();
 close $fh;


#write file
$csv->eol ("\n");
open my $fh_out, ">:encoding(utf8)", $output_file or die "$output_file
+: $!";
 $csv->print ($fh_out, $_) for @rows;
 close $fh_out or die "$output_file: $!";


 print "finish!\n";
[download]

you also need this file 951536_in.csv:

a1,a2,a3
b1,b2,b3
c1,c2,c3
[download]

and the output should be like this 951536_out.csv:

abc1,aasd2,axyz
abc1,basd2,bxyz
abc1,casd2,cxyz
[download]