#!/usr/bin/perl
use strict;
use warnings;
use Array::Diff;

if (@ARGV != 2){
    die "Usage: $0 file_1 file_2";
}

my $diff = Array::Diff->diff(packages($ARGV[0]), packages($ARGV[1]));

print "Packages only in '$ARGV[0]':\n";
print join(" ", @{$diff->deleted}), "\n";

print "Packages only in '$ARGV[1]':\n";
print join(" ", @{$diff->added}), "\n";

sub packages {
    my $fn = shift;
    open my $file, '<', $fn
        or die "Can't open file '$fn' for reading: $!";
    my @packages = 
        map  { $_->[0] } 
        grep { $_->[1] eq 'install' } 
        map  { chomp; [ split m/\s+/, $_, 2 ] }
        <$file>;
    close $file;
    return \@packages;
}