jonesd14:

The first half is pretty good. There are a few quibbles, but nothing bad. For the second half, though, you're doing *far* too much work to get the best key/value from the hash. I'dd suggest something more like this:

my ($bestVal, $bestKey) = (-1);
foreach my $key (@keys) {
    if ($hash{$key} > $bestVal) {
        ($bestVal, $bestKey) = ($hash{$key}, $key);
    }
}
print "The most frequent word in $ARGV[0] is $bestKey, which was seen 
+$bestVal times.\n";
[download]

Now on to a few of the quibbles:

• Your variable names are good except one two: %hash and @arrays.
• chomp $word; is unnecessary, since you just split the string up at non-word characters. Similarly, the regex substitution to remove whitespace is redundant.
• If your file is big, you may run out of memory because you're reading the entire file at once. You might try:

  while (my $line = <FILE>) {
  [download]

  This has the additional advantage of removing the need for the @arrays variable.

I didn't see any real problems, just unnecessary work. Nice work!

Update: Updated first quibble.

...roboticus

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