Berries can be harvested either by hand or with an Autonomous User or another block that emulates right clicks.

In a pack with no tech mods, there's no way to automatically pick berries. I suggest the ability to automatically collect berries with a piston.

When a berry bush is pushed with a piston, the bush block will be moved. It won't break. However, if the berries were ripe, the berries would fall off and drop as an item.