#!/usr/bin/env perl

use strict;
use warnings;

use Data::Dumper qw( Dumper );

my $string = "Hello World!\n  Oh poor Yorick, his world I knew well ye
+s I did";

# No change up to here
# then just

map ++$_,@count{split /\W+/,uc $string};

# that's it
print "Word count:  ", Dumper(%count);

1;
[download]

Update: forgot the case-insensitiveness and changed the string to upper case