HOME Set automatically by login(1) from the user's login
directory in the password file (passwd(4)). This
environment variable also functions as the default
argument for the cd builtin.
PATH The default search path for executables. See the above
section Path Search.
CDPATH The search path used with the cd builtin.
MAIL The name of a mail file, that will be checked for the
arrival of new mail. Overridden by MAILPATH.
MAILCHECK The frequency in seconds that the shell checks for the
arrival of mail in the files specified by the MAILPATH
or the MAIL file. If set to 0, the check will occur at
each prompt.
MAILPATH A colon ':' separated list of file names, for the shell
to check for incoming mail. This environment setting
overrides the MAIL setting. There is a maximum of 10
mailboxes that can be monitored at once.
PS1 The primary prompt string, which defaults to '$ ',
unless you are the superuser, in which case it defaults
to '# '.
PS2 The secondary prompt string, which defaults to '> '.
PS4 Output before each line when execution trace (set -x) is
enabled, defaults to '+ '.
IFS Input Field Separators. This is normally set to
⟨space⟩, ⟨tab⟩, and ⟨newline⟩. See the White Space
Splitting section for more details.
TERM The default terminal setting for the shell. This is
inherited by children of the shell, and is used in the
history editing modes.
HISTSIZE The number of lines in the history buffer for the shell.
PWD The logical value of the current working directory.
This is set by the cd command.
OLDPWD The previous logical value of the current working
directory. This is set by the cd command.
PPID The process ID of the parent process of the shell.
