LayerMask.value  

// Casts a ray using the layer mask,
// which can be modified in the inspector.

var mask : LayerMask = -1;
function Update () {
    if (Physics.Raycast (transform.position, transform.forward, 100, mask.value)) {
        Debug.Log("Hit something");
    }
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public LayerMask mask = -1;
    void Update() {
        if (Physics.Raycast(transform.position, transform.forward, 100, mask.value))
            Debug.Log("Hit something");
        
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public mask as LayerMask = (-1)

    def Update():
        if Physics.Raycast(transform.position, transform.forward, 100, mask.value):
            Debug.Log('Hit something')