RequireComponentNamespace: UnityEngine

The RequireComponent attribute lets automatically add required component as a dependency.

When you add a script which uses RequireComponent, the required component will automatically be added to the game object. This is useful to avoid setup errors. For example a script might require that a rigid body is always added to the same game object. Using RequireComponent this will be done automatically, thus you can never get the setup wrong.
// Mark the PlayerScript as requiring a rigidbody in the game object.
@script RequireComponent(Rigidbody)

function FixedUpdate() { rigidbody.AddForce(Vector3.up); }
C# Example:
[RequireComponent (typeof (Rigidbody))]
public class PlayerScript : MonoBehaviour {
	void FixedUpdate()  {
RequireComponent Require a single component.