id, Not $USER and $UIDRecently I was reminded that $USER is often not defined, of that it
can be redefined any time. This is not only less secure than id it’s a
pain in the ass because you never can rely on it being there. Just don’t
use it, like ever. Here are the equivalent that are always there:
$USER -> id -nu
$UID -> id -u
$GROUP -> id -ng
$GID -> id -g
The id command is on everything including BusyBox containers. Go get
on one right now and see if it has $USER. I’ll give you a hint: it
doesn’t.