how to make animation work once when enter a trigger in unity code example

Example 1: c# unity animation trigger

//Attach this script to a GameObject with an Animator component attached.
//For this example, create parameters in the Animator and name them “Crouch” and “Jump”.
//Apply these parameters to your transitions between states.

//This script allows you to trigger an Animator parameter and reset the other that could possibly still be active. Press the up and down arrow keys to do this.

using UnityEngine;

public class Example : MonoBehaviour
{
    Animator m_Animator;    
  	
  	void Start()
    {
        //Get the Animator attached to the GameObject you are intending to animate.
        m_Animator = gameObject.GetComponent<Animator>();
    }    
  	
  	void Update()
    {
        //Press the up arrow button to reset the trigger and set another one
        if (Input.GetKey(KeyCode.UpArrow))
        {
            //Reset the "Crouch" trigger
            m_Animator.ResetTrigger("Crouch");      
          
          	//Send the message to the Animator to activate the trigger parameter named "Jump"
            m_Animator.SetTrigger("Jump");
        }       
      	
      	if (Input.GetKey(KeyCode.DownArrow))
        {
            //Reset the "Jump" trigger
            m_Animator.ResetTrigger("Jump");            
          	
          	//Send the message to the Animator to activate the trigger parameter named "Crouch"
            m_Animator.SetTrigger("Crouch");
        }
    }
}

Example 2: how to create and trigger a function unity animation events

// Animation Event example
// Small example that can be called on each specified frame.
// The code is executed once per animation loop.using UnityEngine;
using System.Collections;public class Example : MonoBehaviour
{
    public void PrintEvent()
    {
        Debug.Log("PrintEvent");
    }
}