Audio clip not triggering

i have an enemy, and i want it so that when im a certain distance from the enemy it triggers a given sound file. given what i have so far, how should i go about making the audio trigger then stop once it has already been played? im very new to this so my minds all jumbled up here

var theEnemy : Transform;

var thePlayer : Transform;

public var soundWhenSeen : AudioClip;

private var hasBeenPlayed : boolean = false;

function Start () {

if (Vector3.Distance (theEnemy, thePlayer) <= 3);

 {
 
 (soundWhenSeen)

 }

}

function Update ()

{

if(soundWhenSeen);

 {
 
 (hasBeenPlayed == true);

 }
 

     if(hasBeenPlayed == true);

     {
 
     (soundWhenSeen);
 
     }
     

}