linux environment variables
There are a lot of environment variables and I won't be able to cover them all... you can check the currently set environment variables with the command "env" or you can check the specific value of a variable with the command echo (e.g : echo $HOME)
HOME - path to home directory
PATH - directory paths to search for executable files.
PS1 - prompt string (e.g : user@box)
SHELL - path of the binary of your current shell (e.g : /bin/bash)
USER - the current username
EDITOR - default editor (e.g : vim)
PWD - present working directory
SSH_AUTH_SOCK - Path to socket for ssh-agent (pubkey authentication)
DISPLAY - variable used by X11 to identify your display ( e.g : primary monitor is :0, ssh remote will be localhost:10.0 which will send their output and receive their input on port tcp 6010 )