How can i make a raycast in my fps game?

[system]

I want it so there is a ray cast in the middle of the camera. The raycast goes far but not infinite. When i shoot my gun, the bullet goes towards where the raycast hits an object. can any one help me with this? Thanks!

[anon16754120]

    function Update()
        {

 if(Input.GetMouseButton(0))

      {
 var ray = camera.ScreenPointToRay(Input.mousePosition);
 var hit : RaycastHit;

 if(Physics.Raycast(ray,hit))
   {

if(hit.transform == instruction)
   {
   inst = true; 

   }

 if(hit.transform == start)
   {

   Debug.Log("start");  
   }

   }

   }

   }