Common Environment Variables
BASH The location of the bash executable file
SHELL The user's login shell.
CPU The type of CPU.
DISPLAY Location where X Windows output goes.
ENV The location of the configuration file for the current shell.
EUID The ID number of the current user.
HISTFILE The filename where past commands are stored.
HISTSIZE The number of past commands that HISTFILE stores for the current session.
HISTFILESIZE The number of past commands that HISTFILE stores for the multiple sessions.
HOME The absolute path of the user's home directory.
HOST The name of the computer.
HOSTNAME HOSTNAME is identical to HOST, but used on certain distributions.
INFODIR The path to the computer's information pages.
LOGNAME The user name of the current user.
MAIL The path to the current user's mailbox file.
MANPATH The path to the computer's man pages.
OLDPWD The path of the directory the user was in prior to the current path.
OSTYPE The type of operating system. Usually this is Linux.
PATH The directory prefixes used to search for programs and files.
Use a colon to separate entries in the PATH variable.
Do not include a period (.) in the PATH variable. A period indicates that the working directory is in the path, and this poses a security risk.
PS1 The characters the shell uses to indicate normal user ($), root user (#) and similar items.
PWD The path of the current working directory.
LANG The language the operating system uses.
PAGER Used by the man command to specify the program in which to display man pages.