Re: Comparing two files

[lyklev]

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...

Read the old file line by line...

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
}

Now do the same for the new pc file, but instead of storing them, see if an entry exists in the database with old pc's:

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);