// Detects if the control key was pressed
function OnGUI() {
var e : Event = Event.current;
if (e.control) {
Debug.Log("Control was pressed.");
}
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
void OnGUI() {
Event e = Event.current;
if (e.control)
Debug.Log("Control was pressed.");

}
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

def OnGUI():
e as Event = Event.current
if e.control:
Debug.Log('Control was pressed.')