Debug.DrawLine
static function DrawLine(start: Vector3, end: Vector3, color: Color = Color.white, duration: float = 0.0f, depthTest: bool = true): void;
Parameters

start Point in world space where the line should start.
end Point in world space where the line should end.
color Color of the line.
duration How long the line should be visible for.
depthTest Should the line be obscured by objects closer to the camera?
Description

Draws a line between specified start and end points.

The line will be drawn in the scene view of the editor. If gizmo drawing is enabled in the game view, the line will also be drawn there. The duration is the time (in seconds) for which the line will be visible after it is first displayed. A duration of zero shows the line for just one frame.

Note: This is for debugging playmode only. Editor gizmos should be drawn with Gizmos.Drawline or Handles.DrawLine instead.
	// Frame update example: Draws a red line from the world-space origin to the point (1, 0, 0) for 1 frame.
	function Update () {
		Debug.DrawLine (Vector3.zero, Vector3 (1, 0, 0), Color.red);
	}
	// Event callback example: Debug-draw all contact points and normals for 2 seconds.
	function OnCollisionEnter(collision : Collision) {
		for (var contact : ContactPoint in collision.contacts) {
			Debug.DrawLine(contact.point, contact.point + contact.normal, Color.green, 2, false);
		}
	}