public Transform targot;

public Transform start;

public Transform end;

void Start()

{

}

void Update()

{

Vector3 normal = (end.position - start.position).normalized;

Vector3 pos = start.position + Vector3.Project(targot.position- start.position, normal);

pos.x = Mathf.Clamp(pos.x, Mathf.Min(start.position.x, end.position.x), Mathf.Max(start.position.x, end.position.x));

pos.y = Mathf.Clamp(pos.y, Mathf.Min(start.position.y, end.position.y), Mathf.Max(start.position.y, end.position.y));

pos.z = Mathf.Clamp(pos.z, Mathf.Min(start.position.z, end.position.z), Mathf.Max(start.position.z, end.position.z));

transform.position = pos;

transform.LookAt(targot);

}