A man in a ship lands on a planet with nothing but sharp grass and quadrupeds. He is trying to find out what happened to a colony ship that supposedly landed there. I don't remember why, but he starts eating the grass. Even though it cuts him up as he eats it, he loses control and cannot stop.
He eventually stops and finds he's been turned into one of the quadrupeds. In this new form, he is still able to get back into his ship and fly away with the colony ship's computer. The computer (I think its name was Moses) had created the grass to keep the colonists alive, because the planet was hostile to them.
I read this book in the late 1970s. I don't remember much more than enjoying it immensely; it was the first book I ever read more than once. I hope this is enough to find the book again.