How do I make an animation play ONCE when a key is pressed?

So I have a punch animation and I have the character punching but in order for me to do so I have to hold down the button T.T! Can you help me?

var theAnimation : AnimationClip;

function OnTriggerStay () {
    if (Input.GetKeyDown("e")) {
        //Other actions here
        if (audio) {
        audio.loop = false;

or try downloading Dastardly banana's weapons package and use their weapons system because they have a melee weapon so u can set it to play ur punch animation