Scripting Reference
Physics.Raycast

static function Raycast (origin : Vector3, direction : Vector3, distance : float = Mathf.Infinity, layerMask : int = kDefaultRaycastLayers) : boolean

Parameters

NameDescription
origin The starting point of the ray in world coordinates.
direction The direction of the ray.
distance The length of the ray.
layerMask A Layer mask that is used to selectively ignore colliders when casting a ray.

Returns

boolean - True when the ray intersects any collider, otherwise false.

Description

Casts a ray against all colliders in the scene.

JavaScript 
    function Update () {
        var fwd = transform.TransformDirection (Vector3.forward);
        if (Physics.Raycast (transform.position, fwd, 10)) {
            print ("There is something in front of the object!");
        }
    }
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!");
        
    }
}
import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Update():
        fwd as Vector3 = transform.TransformDirection(Vector3.forward)
        if Physics.Raycast(transform.position, fwd, 10):
            print('There is something in front of the object!')
Notes: This function will return false if you cast a ray from inside a sphere to the outside; this in an intended behaviour. If you move colliders from scripting or by animation, there needs to be at least one FixedUpdate executed so that the physics library can update it's data structures, before a Raycast will hit the collider at it's new position.

static function Raycast (origin : Vector3, direction : Vector3, out hitInfo : RaycastHit, distance : float = Mathf.Infinity, layerMask : int = kDefaultRaycastLayers) : boolean

Parameters

NameDescription
origin The starting point of the ray in world coordinates.
direction The direction of the ray.
distance The length of the ray.
hitInfo If true is returned, hitInfo will contain more information about where the collider was hit (See Also: RaycastHit).
layerMask A Layer mask that is used to selectively ignore colliders when casting a ray.

Returns

boolean - True when the ray intersects any collider, otherwise false.

Description

Casts a ray against all colliders in the scene and returns detailed information on what was hit.

JavaScript 
    function Update () {
        var hit : RaycastHit;
        if (Physics.Raycast (transform.position, -Vector3.up, hit)) {
            var distanceToGround = hit.distance;
        }
    }
using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Update() {
        RaycastHit hit;
        if (Physics.Raycast(transform.position, -Vector3.up, out hit))
            float distanceToGround = hit.distance;
        
    }
}
import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Update():
        hit as RaycastHit
        if Physics.Raycast(transform.position, -Vector3.up, hit):
            distanceToGround as single = hit.distance
Another example:
JavaScript 
    // Raycast up to 100 meters down
    function Update () {
        var hit : RaycastHit;
        if (Physics.Raycast (transform.position, -Vector3.up, hit, 100.0)) {
            var distanceToGround = hit.distance;
        }
    }
using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Update() {
        RaycastHit hit;
        if (Physics.Raycast(transform.position, -Vector3.up, out hit, 100.0F))
            float distanceToGround = hit.distance;
        
    }
}
import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Update():
        hit as RaycastHit
        if Physics.Raycast(transform.position, -Vector3.up, hit, 100.0F):
            distanceToGround as single = hit.distance

static function Raycast (ray : Ray, distance : float = Mathf.Infinity, layerMask : int = kDefaultRaycastLayers) : boolean

Parameters

NameDescription
ray The starting point and direction of the ray.
distance The length of the ray.
layerMask A Layer mask that is used to selectively ignore colliders when casting a ray.

Returns

boolean - True when the ray intersects any collider, otherwise false.

Description

Same as above using ray.origin and ray.direction instead of origin and direction.

JavaScript 
    var ray = Camera.main.ScreenPointToRay (Input.mousePosition);
    if (Physics.Raycast (ray, 100)) {
        print ("Hit something");
    }
using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
    void Example() {
        if (Physics.Raycast(ray, 100))
            print("Hit something");
        
    }
}
import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public ray as Ray = Camera.main.ScreenPointToRay(Input.mousePosition)

    def Example():
        if Physics.Raycast(ray, 100):
            print('Hit something')

static function Raycast (ray : Ray, out hitInfo : RaycastHit, distance : float = Mathf.Infinity, layerMask : int = kDefaultRaycastLayers) : boolean

Parameters

NameDescription
ray The starting point and direction of the ray.
distance The length of the ray.
hitInfo If true is returned, hitInfo will contain more information about where the collider was hit (See Also: RaycastHit).
layerMask A Layer mask that is used to selectively ignore colliders when casting a ray.

Returns

boolean - True when the ray intersects any collider, otherwise false.

Description

Same as above using ray.origin and ray.direction instead of origin and direction.

JavaScript 
    var ray = Camera.main.ScreenPointToRay (Input.mousePosition);
    var hit : RaycastHit;
    if (Physics.Raycast (ray, hit, 100)) {
        Debug.DrawLine (ray.origin, hit.point);
    }
using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
    public RaycastHit hit;
    void Example() {
        if (Physics.Raycast(ray, out hit, 100))
            Debug.DrawLine(ray.origin, hit.point);
        
    }
}
import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public ray as Ray = Camera.main.ScreenPointToRay(Input.mousePosition)

    public hit as RaycastHit

    def Example():
        if Physics.Raycast(ray, hit, 100):
            Debug.DrawLine(ray.origin, hit.point)