How do I properly find double entries in two files in Perl? - perl

Question

Let's say I have two files with lists of ip-addresses. Lines in the first file are unique. Lines in the second may or may not be the same as in the first one.
What I need is to compare two files, and remove possible doubles from the second file in order to merge it with the base file later.
I've managed to write the following code and it seems to work properly, but I have a solid feeling that this code can be improved or I may be totally missing some important concept.
Are there any ways to solve the task without using complex data structures, i.e. hashrefs?
#!/usr/bin/perl
use strict;
use warnings;
my $base = shift #ARGV;
my $input = shift #ARGV;
my $res = 'result.txt';
open ("BASE","<","$base");
open ("INP","<","$input");
open ("RES", ">", "$res");
my $rhash = {}; # result hash
while (my $line = <BASE>) {chomp($line); $rhash->{$line}{'res'} = 1;} # create uniq table
while (my $line = <INP>) { chomp($line); $rhash->{$line}{'res'}++; $rhash->{$line}{'new'} = 1; } # create compare table marking it's entries as new and incrementing double keys
close BASE;
close INP;
for my $line (sort keys %$rhash) {
next if $line =~ /\#/; # removing comments
printf("%-30s%3s%1s", $line, $rhash->{$line}{'res'}, "\n") if $rhash->{$line}{'res'} > 1; # kinda diagnosti output of doubles
if (($rhash->{$line}{'new'}) and ($rhash->{$line}{'res'} < 2)) {
print RES "$line\n"; # printing new uniq entries to result file
}
}
close RES;

Answer 1

If I understand correctly file1 and file2 each contain ips (unique in each file) And you want to get ips in file2 not in file1. If so, then maybe the following code achieves your goal.
Although it seems your code will do it, this might be clearer.
#!/usr/bin/perl
use strict;
use warnings;
my $base = shift #ARGV;
my $input = shift #ARGV;
my $res = 'result.txt';
open ("BASE","<","$base") or die $!;
open ("INP","<","$input") or die $!;
open ("RES", ">", "$res") or die $!;
my %seen;
while (my $line = <BASE>) {
chomp $line;
$seen{$line}++;
}
close BASE or die $!;
while (my $line = <INP>) {
chomp $line;
print RES "$line\n" unless $seen{$line}; # only in file2 not in file1
}
close INP or die $!;
close RES or die $!;