You haven't printed out the strings you're trying to compare:

   $_ = "Priority Kirkgate, PC7588\n";
   @fields = split /,/, $_ ;
   print "PC string from NEW list: >>$fields[1]<<";
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This code will have your PC code with a leading space, and the rest of your code won't match that.

Also, it's not really efficient to read through the $old_file for every comparison. I'd read new computers into a hash and then check while stepping through $old_file whether the computer is known or not:

use strict;
my %new_pc;

...

while (<IN1>) {
   chomp;
   $count_in++;
   @fields = split /,/, $_;
   $PC_NO  = $fields[1];
   $PC_NO =~ s/\s*//g;
   $new_pc{ $PC_NO } = 1;
};

...

while (<IN2>) {
   chomp;
   if (/CN=(PC\d+)\.OU/) {
       my $pc = $1;
       if (exists $new_pc{ $pc }) {
           # $pc is old and new, hence has survived
           delete $new_pc{ $pc };
       } else {
           # $pc is old but not new, hence has been removed
       };
   } else {
      warn "Ignoring line >>$_<<";
   };
};

# All PCs in %new are now really new:
for my $pc (keys %new) {
    print "$pc is new\n";
};
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I don't know exactly where your problem is; but if I had to do that, I might write it like this, using a module to parse the CSV:

use IO::File;
my %old =
    map { $_->[1] => $_->[0] }
    map { chomp; [ split /,\s*/ ] }
    IO::File->new("<$file_old")->getlines;

use Tie::Handle::CSV;
my %new =
    map { ( $_->{'CN'} => $_ ) }
    map { { map { /(.*)=(.*)/ } split /\.(?=[A-Z]+=)/, $_->[3] } }
    Tie::Handle::CSV->new($file_new,header=>0)->getlines;

# now %old and %new are keyed by PC ID.
# you can use the standard techniques for finding keys that
# are in one but not the other, e.g.

my @new_PCs = grep { not exists $old{$_} } sort keys %new;
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Cheers,

Brent

Your program has a couple of problems:

First, you are splitting on comma's, then the pc no (the first field) has index 0, index 1 gets you the ip-address.

Next, you are reading the entire second file for each line found in the first file, that will give you some serious I/O for big files.

Perl is not very good at finding out whether something is in a list. If you want to do that, think of a hash in stead. Lists are for processing bulk data element by element. Keeping this in mind, let's rewrite the program.

Assuming you have two files, pcs_old.csv and pcs_new.csv, starting with the opening stuff:

use strict;
use warnings;
open (OLD, "<pcs_old.csv");
open (NEW, "<pcs_new.csv");

my %old; # where pc numbers will get stored...
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while (<OLD>) {
   chomp;
   my @fields = split /,/;
   my $pc = $fields[0];   # get the first field
   $pc =~ s/"//g;         # get rid of the quotes
   $old {$pc} = 1;        # make an entry in the hash
}
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while (<OLD>) {
   chomp;
   my @fields = split /,/;
   my $pc = $fields[0];   # get the first field
   $pc =~ s/"//g;         # get rid of the quotes
   if (! exists $old {$pc}) {
      # the new pc file has a pc which did not exist
      # in the old pc file
      print "new PC found: $pc\n";
   }
}
# and cleanup
close (OLD);
close (NEW);
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