GNU cp already has the --one-file-system option.

Possibly mv might also benefit from this option to error out on EXDEV?

Feel free to discuss these things on coreutils@gnu.org

We try to be accomodating, and your suggestions here definitely have merit and are worth further discussion.

Thanks, also for your comments on the other one. I wish I could make a qualified analysis of the code snippet, but I'm not up to it.

Adding -x / --one-file-system is all constructive suggestions I have regarding the command.

Presumably mv would benefit even more. At least with cp a copy was explicitly asked for.