Trigger collider information

I have 1 object with a collider with isTrigger true. How to detect the number of objects inside the collider and assign each object a variable?

What I want to achieve is, if 2 objects are inside the collider, find the nearest object and do action. If only 1 object, just do the action.

you can track and keep the number or count of the objects present in your collider. You can declare a variable count and in your OnTriggerEnter() increment it by 1 and in your OnTriggerExit() decrement it by 1. So now the value of count will tell you the number of objects present inside the collider.

First, non-collider trigger solutions are easier but less accurate for this task. For example, Physics.OverlapSphere(). But there is a way to do it with a trigger.

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

 public class Bug2 : MonoBehaviour {

	private List<Collider> colliders = new List<Collider>();

	void Update () {
		if (colliders.Count == 1) {
			Debug.Log ("Do action based on 1");
		}
		else if (colliders.Count == 2) {
			Debug.Log ("Find the nearest and do action for 2");
		}
	}

	void OnTriggerStay(Collider col) {
		colliders.Add (col);
	}

	void LateUpdate () {
		colliders.Clear ();
	}
}

At each frame, when you reach Update() ‘colliders’ will be a list of all the colliders found in the OnTriggerStay(). You can compare the two (or more) to see which is closest.

I will explain you more what the guys were trying to tell you,
I will use tags.
assign a tag to your objects that will enter the trigger.
Here i have assigned “guest”.

using UnityEngine;
using System.Collections;
 
public class MyClass : MonoBehaviour 
{ 
    private int count = 0;
 
    void Update () 
	{
       if (colliders.Count == 1) 	   
         Debug.Log ("Do action based on 1");
       
       else if (colliders.Count == 2) 
         Debug.Log ("Find the nearest and do action for 2");       
    }
 
    void OnTriggerEnter(Collider col)
	{
       if(col.transform.tag == "guest")
			count++;
    }
 
    void OnTriggerExit(Collider col)
	{
       if(col.transform.tag == "guest")
			count--;
    }
}