This is generally good advice, but redo tries to do something else: it actually tests all your shells, and picks the one that supports the features we're expect

This is generally good advice, but redo tries to do something else: it actually tests all your shells, and picks the one that supports the features we're expecting. That way we can set a minimum baseline. All the features in the article are tested by redo, so at least in your redo scripts, you can assume those features are available. Maybe someone can generalize the "redo-sh" feature somehow.