To display all of the environment variables, in alphabetical order, that are already set for your shell, type the following:
$ set | less
BASH=/bin/bash
COLORS=/etc/DIR_COLORS.xterm
COLUMNS=118
DISPLAY=:0.0
HOME=/home/fcaen
HOSTNAME=einstein
Also, you can concatenate a string to an existing variable:
$ export PATH=$PATH:/home/fcaen
To list your bash’s environment variables:
$ env