[casey2]

This is why I dislike sites like stackoverflow. If I needed a quick lookup the v7 manpage explains it better, the v6 doesn't have it, but that's because unix didn't have bourne shell til V7

https://man.cat-v.org/unix_7th/1/sh#:~:text=%3C%26digit%0A%2...

Seriously when it comes to unix RTFM RTFM RTFM and you'll get the top comment on SO and HN rolled into one.