PATH - Display lists directories the shell searches, for the commands.
HOME - User's home directory to store files.
TERM - Set terminal emulator being used by UNIX.
PS1 - Display shell prompt in the Bourne shell and variants.
MAIL - Path to user's mailbox.
TEMP - Path to where processes can store temporary files.
JAVA_HOME - Sun (now Oracle) JDK path.
ORACLE_HOME - Oracle database installation path.
TZ - Timezone settings
PWD - Path to the current directory.
HISTFILE - The name of the file in which command history is saved
HISTFILESIZE -The maximum number of lines contained in the history file
HOSTNAME -The system's host name
LD_LIBRARY_PATH -It is a colon-separated set of directories where libraries should be searched for.
USER -Current logged in user's name.
DISPLAY -Network name of the X11 display to connect to, if available.
SHELL -The current shell.
TERMCAP - Database entry of the terminal escape codes to perform various terminal functions.
OSTYPE - Type of operating system.
MACHTYPE - The CPU architecture that the system is running on.
EDITOR - The user's preferred text editor.
PAGER - The user's preferred text pager.
MANPATH - Colon separated list of directories to search for manual pages.