Event.button

Description

Which mouse button was pressed.

0 means left mouse button, 1 means right mouse button, 2 means middle mouse button. Used in EventType.MouseDown and EventType.MouseUp events.

// Detect which mouse button is currently pressed
// and print it.
function OnGUI() {
    var e : Event = Event.current;
    if(e.button == 0 && e.isMouse){
        Debug.Log("Left Click");
    } else if(e.button == 1) {
        Debug.Log("Right Click");
    } else if (e.button == 2) {
        Debug.Log("Middle Click");
    } else if (e.button > 2) {
        Debug.Log("Another button in the mouse clicked");
    }
}

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void OnGUI() {
        Event e = Event.current;
        if (e.button == 0 && e.isMouse)
            Debug.Log("Left Click");
        else
            if (e.button == 1)
                Debug.Log("Right Click");
            else
                if (e.button == 2)
                    Debug.Log("Middle Click");
                else
                    if (e.button > 2)
                        Debug.Log("Another button in the mouse clicked");
                    
    }
}