macOS:
HOME
LOGNAME
OLDPWD
PATH
PWD
SHELL
SHLVL
SSH_CLIENT
SSH_CONNECTION
SSH_TTY
TERM
TMPDIR
USER
_
e.g.
HOME=/Users/bts
LOGNAME=bts
OLDPWD=/Users/bts
PATH=/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin
PWD=/Users/bts
SHELL=/bin/zsh
SHLVL=1
SSH_CLIENT=192.168.2.99 39690 22
SSH_CONNECTION=192.168.2.99 39690 192.168.2.148 22
SSH_TTY=/dev/ttys000
TERM=xterm-256color
TMPDIR=/var/folders/qv/bm6dlyd94x5fs6qpkfpj0jsr0000gq/T/
USER=bts
_=/usr/bin/env