my %index;
foreach my $entry (@file1) {
    if (not exists $index{$entry}) {
        $index{$entry} = 1
    }
}

foreach my $entry (@file2) {
    if (not exists $index{$entry}) {
        $index{$entry} = 2
    }
    else {
        $index{$entry} += 2;
    }
}

foreach my $entry (keys %index) {
    if ($index{$entry} == 1) {
        print "Entry $entry is only in file one\n";
    }
    elsif ($index{$entry} == 2) {
        print "Entry $entry is only in file two\n";
    }
    elsif ($index{$entry} == 3) {
        print "Entry $entry is in both files\n";
    }
    else {
        print "Entry $entry is screwed up!\n";
    }
}