mirod's answer is well explained, and Hofmator and mugwumpjism (what a beaut of a name) have shown how Perl can make something very... um.. concise.

I noticed that you are a novice monk and therefor might not be aware of the great deal of information that is available for you via the Search box at the top of your screen while on PerlMonks. Typing the words "unique elements" in the box returned many articles that contain a great deal of information related to your question.

One of the benefits of using the search would be that you would not have to wait for an answer to your question, it is already there. You might also find out quite a bit more that you had originally asked.

Good luck, welcome, and don't forget the Search box.