Open/Close Door only if player is near the Door

Hi I have an Script in which the "Player" can open and close door but he can do it wherever he is. Also a Text ("Press E to Open Door"/"Press F to close Door" appears wherever the player is. What I need help is how can I do that the Player only can open/close the door when he is near it.(also the text). I have an Empty Gameobject (this one has the Script) which is the Hingle and a cube as the door. using UnityEngine; using System.Collections;

 public class doorOpenandClose : MonoBehaviour {
 
     //Text variables
     public bool T_ActivatedOpen = true;
     public bool T_ActivatedClose = false;
     public bool activateTrigger = false;
 
     public GameObject textO;
     public GameObject textC;
 
     //Animator variables
     Animator animator;
     bool doorOpen;
     //Sound variables
     public GameObject doorOpenSound;
     public GameObject doorCloseSound;
 
 
 
 
 
 
     void Start () { //what happens in the beginning of the game.
         textC.SetActive (false);
         textO.SetActive (false);
         T_ActivatedOpen = true;
         T_ActivatedClose = false;
 
         animator = GetComponent<Animator> ();
         doorOpen = false;
 
 
         doorCloseSound.SetActive (false);
         doorOpenSound.SetActive (false);
 
 
 
     
     }
     
 
     void Update () { //The main function wich controlls how the system will work.
 
         if (T_ActivatedOpen == true)
             T_ActivatedClose = false;
 
         else if (T_ActivatedClose == true)
             T_ActivatedOpen = false;
 
         if (activateTrigger && Input.GetKeyDown (KeyCode.E)) //For some reaseon you can't have both E (open and close).
             {
                 
                 T_ActivatedOpen = false;
                 T_ActivatedClose = true;
                 textO.SetActive (false);
                 textC.SetActive (true);
                 doorOpen = true;
 
                 doorOpenSound.SetActive (true);
                 doorCloseSound.SetActive (false);
 
             if (doorOpen) 
             {
                 doorOpen = true;
                 doorController ("Open");
             }
                 
             }
             else if(T_ActivatedClose && activateTrigger && Input.GetKey (KeyCode.F)) 
             {
                 T_ActivatedOpen = true;
                 T_ActivatedClose = false;
                 textO.SetActive (true);
                 textC.SetActive (false);
 
                 doorCloseSound.SetActive (true);
                 doorOpenSound.SetActive (false);
     
             if (doorOpen) 
             {
                 doorOpen = false;
                 doorController ("Close");
             }
                 
             } 
     }
 
 
                                                         
     void OnTriggerEnter(Collider col) //If you enter the trigger this will happen.
     {
         if(col.gameObject.tag == "Player")
         {
 
                 activateTrigger = true;
             if((T_ActivatedOpen == true))
             textO.SetActive (true);
 
             if((T_ActivatedClose == true))
                 textC.SetActive (true);
         }
         
     }
 
 
     void OnTriggerExit(Collider col) //If you exit the trigger this will happen.
     {
         if(col.gameObject.tag == "Player")
         {
             textO.SetActive (false);
             textC.SetActive (false);
             activateTrigger = false;
         }
 
     }
 
     void doorController(string direction) //Animator function.
     {
         animator.SetTrigger(direction);
     }
         
 }