GameObject.CreatePrimitive  

// Create a plane, sphere and cube in the scene.

function Start () {
var plane : GameObject = GameObject.CreatePrimitive(PrimitiveType.Plane);

var cube : GameObject = GameObject.CreatePrimitive(PrimitiveType.Cube);
cube.transform.position = Vector3(0, 0.5, 0);

var sphere : GameObject = GameObject.CreatePrimitive(PrimitiveType.Sphere);
sphere.transform.position = Vector3(0, 1.5, 0);

var capsule : GameObject = GameObject.CreatePrimitive(PrimitiveType.Capsule);
capsule.transform.position = Vector3(2, 1, 0);

var cylinder : GameObject = GameObject.CreatePrimitive(PrimitiveType.Cylinder);
cylinder.transform.position = Vector3(-2, 1, 0);
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
void Start() {
GameObject plane = GameObject.CreatePrimitive(PrimitiveType.Plane);
GameObject cube = GameObject.CreatePrimitive(PrimitiveType.Cube);
cube.transform.position = new Vector3(0, 0.5F, 0);
GameObject sphere = GameObject.CreatePrimitive(PrimitiveType.Sphere);
sphere.transform.position = new Vector3(0, 1.5F, 0);
GameObject capsule = GameObject.CreatePrimitive(PrimitiveType.Capsule);
capsule.transform.position = new Vector3(2, 1, 0);
GameObject cylinder = GameObject.CreatePrimitive(PrimitiveType.Cylinder);
cylinder.transform.position = new Vector3(-2, 1, 0);
}
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

def Start():
plane as GameObject = GameObject.CreatePrimitive(PrimitiveType.Plane)
cube as GameObject = GameObject.CreatePrimitive(PrimitiveType.Cube)
cube.transform.position = Vector3(0, 0.5F, 0)
sphere as GameObject = GameObject.CreatePrimitive(PrimitiveType.Sphere)
sphere.transform.position = Vector3(0, 1.5F, 0)
capsule as GameObject = GameObject.CreatePrimitive(PrimitiveType.Capsule)
capsule.transform.position = Vector3(2, 1, 0)
cylinder as GameObject = GameObject.CreatePrimitive(PrimitiveType.Cylinder)
cylinder.transform.position = Vector3(-2, 1, 0)