Regular expression - match all words but match unique words only once

Question

Is it possible to use a regular expression to match all words but match unique words only once? I am aware there are other ways of doing this however I\'m interested

Answer 1

Exactly as maček's answer, but with an extra \b before the back-reference, otherwise if you had

glass shoes door window door glasses. window glasses sunglasses

You'd miss out a match for glasses as it finds it in the word sunglasses.

/(\w+\b)(?!.*\b\1\b)/

Answer 2

For search distinct words in multiline text use [\s\S] instead of .

(\b\w+\b)(?![\s\S]*\b\1\b)

Answer 3

Pretty close, just readd the \b in the negative lookahead

/(\w+\b)(?!.*\1\b)/

See it on Rubular