|Perl: the Markov chain saw|
Match a word if it follows itself:
Correct the problem (remove the second word):
\b matches a word break. It is zero bytes long and lifes on both sides of a word. In the words "|sides| |of| |a| |word|", each | shows the position of a \b.
The regex matches a word break (which is also before the first and behind the last word in a string/on a line), followed by a word (\w+) containing one or more of [a-zA-Z0-9_] followed by a non-word-char (\W) (which is everything but the chars listed before).
You know $1, which contains the contents of the first ( ) in the last executed regex? \1 is the same, but it's for the current regex and contains the word we found before by using \w+.
Adding another word-break at the end keeps us from matching /in/information/, because (\w+)\W\1 would match the in (as \w+ in ( ) going to \1), the / as match for \W and "in" of "information" for \1, because \1 contains the "in" from the \w+ match.
The first regex could be used on your whole text, there is no need to split it into lines.
Speaking of texts, some suggestions: