Aside from not showing any attempt at solving the problem, which has already been mentioned, this has something of the odour of homework. With that in mind the references you need are: perlre, perlretut and possibly perlreref.

This matching of words is somewhat tricky, firstly due to managing apostrophes (which often look like single quote marks) and secondly due to the fact that often a word you might wish to match is embedded in another word.