using Arduino to control an LED powered from an outside source

Hey guys,
i'm kinda new to the arduino platform and have a question.
i'm a programmer with not a lot of background in electronics so don't make fun of me :smiley:

i have an LED stripe that is connected to a 12V dc power supply.

now, i want to control this LED stripe using my arduino,
i have a momentary switch i want to use to accomplish this for the time being (later i want to move to controlling it using wifi).

i know i can just buy a relay, but i dont have one available right now,
so my question is, how can i achieve this (if at all) using only an arduino and a momentary switch.
i thought maybe i can somehow short circuit the LED, is this possible?

thanks for the help!

you need a relay or switching device of some sort. You can't have 12v going through arduino. imagine the 12v is 120v would you still not use a relay?