First Column Modified

#!/usr/bin/perl
use strict;
use warnings;
use utf8;
use open ':utf8';
open my $in, 'data.csv' or die;
open my $out, '>', 'data.mem' or die;
my @a;
while (<$in>) {
  chomp;
  my @b = split ',';
  push @a, shift @b;
}
map { chop; print $out '0' . $_ , "\n" } @a;
close $out;
close $in;