I'm not the parent commenter and I'm not on a Mac, but I assume it's the bash glob for a single character match (much like * matches multiple characters, ? matches a single character).
Which means the actual file path should be something like `/dev/rdisk0`.
Edit: oh, I guess you meant the ? in `bs=?M`, in which case I don't know. Probably damurdock's way of not committing to a particular value in their post.
Edit: oh, I guess you meant the ? in `bs=?M`, in which case I don't know. Probably damurdock's way of not committing to a particular value in their post.