How to do "nothing" in a frag program?

I'm trying to create a shader. It is the Unity standard specular shader with a grab pass and extra frag program at the end. How do I do nothing in the frag program as if it wasn't even there? Is it possible to do that?

Code (csharp):

1.  
2. Shader "Standard (Specular setup)-FrostedGlass"
3. {
4.     Pass
5.         {
6.             Name "FORWARD"
7.             Tags { "LightMode" = "ForwardBase" }
8.            //...
9.        }
10.  
11.       //..all of these original passes are in the program
12.     //then at the end I have added:
13.  
14.         GrabPass
15.          {
16.               Tags{ "LightMode" = "Always" }
17.           }
18.  
19.           Pass
20.          {
21.               Tags{ "LightMode" = "Always" }
22.                CGPROGRAM
23.                #pragma vertex vert
24.                #pragma fragment frag
25.  
26.                struct appdata_t
27.                {
28.                          float4 vertex : POSITION;
29.                          float2 texcoord: TEXCOORD0;
30.                 };
31.  
32.                struct v2f
33.                {
34.                          float4 vertex : POSITION;
35.                          float4 uvgrab : TEXCOORD0;
36.                  };
37.  
38.                    //...
39.                  fixed4 frag(v2f i) : COLOR      
40.                  {
41.                                //return some value so nothing happens. As if this "Frag" didn't even exist.
42.                  }
43.    }    
44.  

 

there's "discard", but it's expensive on mobile

 

What is the purpose of the shader if it is not meant to display anything? Do you want to use the gpu for processing?

 

Ok. Thanks. That was what I was looking for.

The shader is the standard shader + a frosted glass effect for transparent areas.
Don't do frosted glass effect for areas which have full opacity. (discard)

I got it somewhat usable at this point:

.