how to update only once in unity

Hello i have a code which moves my main camera to other game objects positions when i press button like if i press button 1 it will move towards object 1 position same for button 2 and 3. Now in my code i have a boolean named as flag which is true in update function then i have multiple public functions for multiple buttons now when i press any button the boolean becomes true and remains true which causes camera to shake because boolean is continously updating please tell me a way that when my camera reaches it final position the flag boolean becomes false and when again i press another button i will become true again here is my code

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class camMOVE : MonoBehaviour {
 
 
 
 public Transform  handleview;
 public Transform pressureview;
 public Transform wallview;
 public Transform sechandleview;
 public Transform pressuretwoview;
 public Transform switchview;
 
 public GameObject handlebtn;
 public GameObject pressurebtn;
 public GameObject wallbtn;
 public GameObject handletwobtn;
 public GameObject pressuretwobtn;
 public GameObject switchbtn;
 
 public GameObject parentobj;
 Animator anim;
 
 
 
 public float transitionSPEED;
 Transform currentVIEW;
 private bool flag = false;
 Vector3 currentangel;
 public List<GameObject> modelparts;
 
 private void Start(){
     handlebtn.SetActive (true);
     pressurebtn.SetActive (false);
     wallbtn.SetActive (false);
     handletwobtn.SetActive (false);
     pressuretwobtn.SetActive (false);
     switchbtn.SetActive (false);
 
     anim = parentobj.GetComponent<Animator> ();
     anim.SetBool ("start", true);
 
 
     //currentVIEW = handleview;
     foreach (GameObject obj in modelparts) {
 
         obj.GetComponent<BoxCollider> ().enabled = false;
     }
 }
 
 private void Update(){
 
 
     if (flag == true) {
         transform.position = Vector3.Lerp (transform.position, 
 currentVIEW.position, Time.deltaTime * transitionSPEED);
 
 
         currentangel = new Vector3 (Mathf.LerpAngle 
 (transform.rotation.eulerAngles.x, currentVIEW.transform.rotation.eulerAngles.x, Time.deltaTime * transitionSPEED),
             Mathf.LerpAngle (transform.rotation.eulerAngles.y, currentVIEW.transform.rotation.eulerAngles.y, Time.deltaTime * transitionSPEED),
             Mathf.LerpAngle (transform.rotation.eulerAngles.z, currentVIEW.transform.rotation.eulerAngles.z, Time.deltaTime * transitionSPEED));
 
         transform.eulerAngles = currentangel;
 
     }
 
 
 
 }
 
 public void Handleview(){
 
     currentVIEW = handleview;
     handlebtn.SetActive (false);
     flag = true;
 
 
 
 
 
 }
 
 public void Pressureview(){
 
     currentVIEW = pressureview;
     pressurebtn.SetActive (false);
     flag = true;
 
 }
 
 public void Wallview(){
 
     currentVIEW = wallview;
     wallbtn.SetActive (false);
     flag = true;
 
 
 
 }
 
 public void Secondhandleview(){
     currentVIEW = sechandleview;
     handletwobtn.SetActive (false);
     flag = true;
 
 
 
 
 }
 
 public void Pressuretwoview(){
     currentVIEW = pressuretwoview;
     pressuretwobtn.SetActive (false);
     flag = true;
 
 
 
 
 }
 
 public void Switchview(){
     currentVIEW = switchview;
     switchbtn.SetActive (false);
     flag = true;
 
 
 
 
 }