I'll give this a try, this should get you going. How about:

my %count;
my $size = 4;          # minimum size of words to count

while (<>) {
        my @words = split;
        foreach my $word (@words) {
                next if length($word) < $size;

                # Count only "real" words, and words with
                # hyphens and apostrophes, like /foo-bar/
                # and /don't/ and /ma'am/
                $count{$word}++ if $word =~ 
                      m/^[a-z][A-Z]+([-'][a-z][A-Z]+)*$/;
        }
}

my %uniq = keys %count;
unless (%uniq) {
        die "No words in the file\n";
}

foreach my $word (keys %count) {
        $final_count    += $count{$word};
        $final_length   += length($word);
}

# Do some other stuff with your hash
[download]

Update: Fixed a small typo