RaycastHit2D.distance

Description

The distance from the ray origin to the impact point.

#pragma strict
public var direction;
function Update() {
	//Cast a ray in the direction specified in the inspector.
	var hit = Physics2D.Raycast(this.gameObject.transform.position, direction);
	//If something was hit.
	if (hit.collider != null) {
		//If the object hit is less than or equal to 6 units away from this object.
		if (hit.distance <= 6.0f) {
			Debug.Log("Enemy In Range!");
		}
	}
}

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour
{
	public Vector2 direction;

	void Update()
	{
		//Cast a ray in the direction specified in the inspector.
		RaycastHit2D hit = Physics2D.Raycast(this.gameObject.transform.position,direction);

		//If something was hit.
		if ( hit.collider != null )
		{
			//If the object hit is less than or equal to 6 units away from this object.
			if(hit.distance <= 6.0f)
			{
				Debug.Log("Enemy In Range!");
			}
		}
	}
}