Perl script to compare two files and report new entries in file 1

Question

I am looking to compare two files. Incoming file from a vendor with IPs and a local file we have been using that will soon be updated with the vendor copy. I would like it it print only the new data that it finds that is not in our copy.

IPV4-vendorlist.txt

10.0.0.0
192.168.1.1
192.168.2.2
192.168.3.3

IPV4-outgoing.txt

10.0.0.0
192.168.1.1
192.168.2.2

In this example, I would like it to print "The following will be added: 192.168.3.3".

Here is the code I have thus far that runs, it just doesn't produce any output:

use strict;

my $fname = 'IPV4-vendorlist.txt';

open my $vendor, "<", $fname
or die "Couldn't open $fname: $!";

my %urls;

while (my $url = <$vendor>) {
  chomp $url;
  $urls{$url} = undef;
}

close $vendor;
$fname = 'IPV4-outgoing.txt';

open my $ourfile, "<", $fname
or die "Couldn't open $fname: $!";

while (my $url = <$ourfile>) {
  chomp $url;
  next if exists $urls{$url}; 
  print "The following will be added: $url";
}

close $ourfile;

Answer 1

Your script (probably) works. There are no IPs in the "outgoing" list which are not also already on the "vendor" list. (Perhaps you meant the other way around? There are addresses on the "vendor" list which are not on the "outgoing" list.)

For what it's worth, standard Unix tools like diff and cmp and comm already provide basic functionality for comparing lists.