Lerper.cs

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

public class Lerper : MonoBehaviour {

    public Transform startPos, endPos;
    public bool repeatable = false;
    public float speed = 1.0f;
    public float duration = 3.0f;

    float startTime, totalDistance;

	// Use this for initialization
	IEnumerator Start () {
        startTime = Time.time;
        totalDistance = Vector3.Distance(startPos.position, endPos.position);
        while(repeatable) {
            yield return RepeatLerp(startPos.position, endPos.position, duration);
            yield return RepeatLerp(endPos.position, startPos.position, duration);
        }
	}
	
	// Update is called once per frame
	void Update () {
        if(!repeatable) {
            float currentDuration = (Time.time - startTime) * speed;
            float journeyFraction = currentDuration / totalDistance;
            this.transform.position = Vector3.Lerp(startPos.position, endPos.position, journeyFraction);
        }
	}

    public IEnumerator RepeatLerp(Vector3 a, Vector3 b, float time) {
        float i = 0.0f;
        float rate = (1.0f / time) * speed;
        while (i < 1.0f) {
            i += Time.deltaTime * rate;
            this.transform.position = Vector3.Lerp(a, b, i);
            yield return null;
        }
    }
}