#!/usr/bin/env perl

use strict;
use warnings;

my $first   = shift;
die "usage: ./script firstfile secondfile" unless $first;
my $second  = shift;
die "usage: ./script firstfile secondfile" unless $second;

my @first   = `cat $first`;
my @second  = `cat $second`;

my %first;
foreach (@first) {
  chomp;
  $first{$_}++;
}
my %second;
foreach (@second) {
  chomp;
  $second{$_}++;
}

# let's run through our list and see which of second is missing
my $missingfromfirst  = 'missingfromfirst.txt';
my $missingfromsecond = 'missingfromsecond.txt';
# ...zeroing out the files frist
system ": > $missingfromfirst";
system ": > $missingfromsecond";

# which items are common to both lists?
my $common  = 'commonentries.txt';
system ": > $common";
my %common;

# if we have an item and it's not in their list, they are we report it as their missing item
system ": > $missingfromsecond";
foreach (@first) {
  chomp;
  system "echo $_ >> $missingfromsecond" unless $second{$_};
  $common{$_}++;
}

system ": > $missingfromfirst";
foreach (@second) {
  chomp;
  system "echo $_ >> $missingfromfirst" unless $first{$_};
  $common{$_}++;
}

foreach (keys %common) {
  system "echo $_ >> $common" if $common{$_} > 1;
}