use strict;
use warnings;

my $fileData = <<DATA;
Greetings,
I've been trying to put a word frequency counter together but I keep getting an
unitialised value in pattern match. I'd be grateful if somebody could let me
know what I'm dong wrong.
I added a line to get some repeated words.
DATA

my %seen;

open my $inFile, '<', \$fileData;
for (grep {chomp; length} <$inFile>) {
    $seen{lc $1}++ while /(\w['\w-]*)/g;
}
close ($inFile);

printf "%5d %s\n", $seen{$_}, $_ for sort { $seen{$b} <=> $seen{$a} } keys %seen;