Mathf.PingPong

Description

PingPongs the value t, so that it is never larger than length and never smaller than 0.

The returned value will move back and forth between 0 and length.

using UnityEngine;

public class Example : MonoBehaviour
{
    void Update()
    {
        // Set the x position to loop between 0 and 3
        transform.position = new Vector3(Mathf.PingPong(Time.time, 3), transform.position.y, transform.position.z);
    }
}