How can I tell if my character controller is in contact with a wall?

This is a duplicate question, however you would go attach a script to your character and add the following function:

 // in js:
 function OnCollisionEnter (other : Collision)
 {
    Debug.Log("I collided!");
    if (other.gameObject.name == "Wall") {
       Debug.Log("Collided with wall!");
    }
 }
 
 // in c#:
 void OnCollisionEnter (Collision other)
 {
    Debug.Log("I collided!");
    if (other.gameObject.name == "Wall") {
       Debug.Log("Collided with wall!");
    }
 }

if you need the information every frame use:

 // in C#:
 void OnCollisionStay (Collision other)
 {
     Debug.Log("I'm colliding!");
     if (other.gameObject.name == "Wall") {
        Debug.Log("Colliding with wall!");
     }
 }

hope it helps