regex steady difference punctuation

what i wish check repetitious difference right unbroken any nonetheless even there punctuation between.

for example:

vivamus vivamus diam, diam, vivamus vivamus diam, diam vivamus

there should 4 graphic hits here.

i can't figure out since isn't working; someone explain since arrangement me repremand formula should be?

thanks.

(\w*(?:[ ,\.])*?)\1

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ps: due difficulty causes, i'm going contend i'm controlling perl engine.