Inside of a shader how can I convert a world direction relevant to a vertex's local position

Hi, I'm actually starting to learn shader coding myself and I really need grass that colellectively "bows" in wave patterns, like a world space wind blows over it, not that weird stuttering the unity tree creator shaders have.

Would you $$anonymous$$d sharing your work in progress or if not, point me to some tutorials that explain this well? Browsing through the "writing shaders" sections of the unity documentation gives me a headache since the pages link to each other in a weird cancerlike circle and don't actually explain basic commands needed.