> There likely happens to be a 'join' program installed on your computer and like any program it can be invoked from your shell. 'join' is a Linux coreutil, so

> There likely happens to be a 'join' program installed on your computer and like any program it can be invoked from your shell. 'join' is a Linux coreutil, so though it might not always be there for strictly UNIX, it will be for Linux. Calling a coreutil part of the shell does make sense in some contexts, and I'd suggest when talking about what you can do with a cli, this is one of those times.