Mouse Drag an Object on a single axis

Mouse Drag an Object on a single axis such as x or y or z , so far i only have

 using UnityEngine;
 using System.Collections;
 
 public class example : MonoBehaviour {
     void Update() {
         Vector3 fwd = transform.TransformDirection(Vector3.forward);
         if (Physics.Raycast(transform.position, fwd, 10))
             print("There is something in front of the object!");
         
     }
 }