Dr. Manhattan:

While there are a few interesting topics, no-one has mentioned that the easiest way to remove the upper-case characters is not to have any in the first place:

my %H;
while (<>) {
   my @words = map { lc }       # map all words to lower case
               split /\s+/, $_; # break $_ into a list of words
   $H{$_}++ for @words;         # add words to hash
}
[download]

If you needed the upper-case versions at some point, then this may not be useful. But people frequently miss the opportunity to clean up the data before storing it, so I thought I'd mention it, just in case.

...roboticus

When your only tool is a hammer, all problems look like your thumb.