There are several ways to do this. A rather short one is:

my $text = " THIS is a variable number of words, spaces  and  punctuat
+ion. ";
my @list = split /\W+/,$text;
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So I'm splitting the text whenever I found one or more characters which are not words.

I don't know whether eliminating empty strings at the beginning and the end of the list is relevant, so I'm leaving this as an exercise to the reader (hint: grep $_,@list might not do what you want if you consider numbers as words).