unity determines if there is a 'person' field in the external text. If so, it instantiates the prefab

This answer refers to ChatGPT
In Unity, you can use the C# language and Unity API to determine if there is a specific field in the external text. The prefab is instantiated when the conditions are met. Here is a basic example code:

using UnityEngine;
using System.IO;

public class Example : MonoBehaviour
{
    public GameObject prefab;

    void Start()
    {
        // 检查文件是否存在
        if (File.Exists("yourfile.txt"))
        {
            // 读取文本文件的所有行
            string[] lines = File.ReadAllLines("yourfile.txt");
            foreach (string line in lines)
            {
                // 检查行中是否包含 "person" 字段
                if (line.Contains("person"))
                {
                    // 实例化预制体
                    Instantiate(prefab, transform.position, Quaternion.identity);
                    break; // 只需要实例化一次
                }
            }
        }
    }
}

In this example, we first check to see if the external text file exists. If there is, we read all the rows and use a foreach loop to iterate over each row. We then check if each row Contains the "person" field using the Contains() method. If the field is found, we Instantiate the prefab with the Instantiate() method and exit the loop with the break keyword after completion.

Note that this example assumes that you have placed an empty gameobject in the scene and added it as a component of this script. This empty gameobject will be used to instantiate the prefab and place it in its place.

You need to drag and drop the prefab into the public variable prefab in this script in order to properly instantiate the prefab when the conditions are met.