Question How to make terrain shader dynamic?

I tried to download the Nature/Terrain/Diffuse Shader and add some custom components to it.
However, I found out that the terrain shader is rendered only when the application is started.
Is there any way to make this shader updated every frame?

 

There's no such thing as a "dynamic" shader, and there's no need to "update a shader" every frame, so I have no idea what you mean. Shaders (being programs that run on the gpu to determine how objects look when rendered) are executed whenever the object that uses them is rendered, which usually means every frame.

Can you describe your problem in more detail?

 

I was trying to modify the vertex position relative to the user position,
and was successful on materials and shaders for regular objects.
However, when I downloaded the terrain shader example and modified it,
I found out that the rendering only occurs at the beginning of the application.
It does not get updated as I update the material variables in the c# script.

 

There's no difference between materials for "regular" objects and terrain. I took a toon terrain surface shader I found online, slapped a vertex shader on it that inflates vertices along their normal direction, and updated the inflation amount every frame at runtime using this simple script:

Code (CSharp):

1.  
2. using UnityEngine;
3.  
4. public class ModifyTerrain : MonoBehaviour
5. {
6.     public float amount = 0;
7.  
8.     MaterialPropertyBlock pb;
9.     Terrain terrain;
10.  
11.     private void Awake()
12.     {
13.         pb = new MaterialPropertyBlock();
14.         terrain = GetComponent<Terrain>();
15.     }
16.  
17.     // Update is called once per frame
18.     void Update()
19.     {
20.         terrain.GetSplatMaterialPropertyBlock(pb);
21.         pb.SetFloat("_Inflation", amount);
22.         terrain.SetSplatMaterialPropertyBlock(pb);
23.     }
24. }
25.  

The material is just a basic terrain material with this bit added as the vertex shader:

Code (CSharp):

1. float _Inflation;
2.  
3. void vert (inout appdata_full v) {
4.     v.vertex.xyz += v.normal * _Inflation;
5. }

Here's the resulting "chubby" terrain: