It may be obvious if you start from the command, but from the other side, I realize that I would also be clueless.

This is an old command, with a lot of better alternatives, that made it fall in shadow. I doubt I will ever see a script using it haha.

Let's turn this into a tiny scavenger hunt instead: "%u %d %s" is what you need to grep for, and Google will not be very useful with "%u %d %s".

Anyway, getting the POSIX man page locally is always a good idea.