Here is an alphabetical list of environment variables that have special meanings in Emacs. Most of these variables are also used by some other programs. Emacs does not require any of these environment variables to be set, but it uses their values if they are set.

CDPATH

Used by the cd command to search for the directory you specify, when you specify a relative directory.

COLORTERM

If this variable is set to the value truecolor, it tells Emacs to use 24-bit true color on text-mode displays even if the terminfo database is not installed. Emacs will use built-in commands to request true color by RGB values instead of the missing terminfo information.

DBUS_SESSION_BUS_ADDRESS

Used by D-Bus when Emacs is compiled with it. Usually, there is no need to change it. Setting it to a dummy address, like unix:path=/dev/null, suppresses connections to the D-Bus session bus as well as autolaunching the D-Bus session bus if not running yet.

EMACSDATA

Directory for the architecture-independent files that come with Emacs. This is used to initialize the variable data-directory.

EMACSDOC

Directory for the documentation string file, which is used to initialize the Lisp variable doc-directory.

EMACSLOADPATH

A colon-separated list of directories(Here and below) to search for Emacs Lisp files. If set, it modifies the usual initial value of the load-path variable (Lisp Libraries). An empty element stands for the default value of load-path; e.g., using EMACSLOADPATH"/tmp:"= adds /tmp to the front of the default load-path. To specify an empty element in the middle of the list, use 2 colons in a row, as in EMACSLOADPATH"/tmp::/foo"=.

EMACSPATH

A colon-separated list of directories to search for executable files. If set, Emacs uses this in addition to PATH (see below) when initializing the variable exec-path (Shell).

EMAIL

Your email address; used to initialize the Lisp variable user-mail-address, which the Emacs mail interface puts into the From header of outgoing messages (Mail Headers).

ESHELL

Used for shell-mode to override the SHELL environment variable (Interactive Shell).

HISTFILE

The name of the file that shell commands are saved in between logins. This variable defaults to ~/.bash_history if you use Bash, to ~/.sh_history if you use ksh, and to ~/.history otherwise.

HOME

The location of your files in the directory tree; used for expansion of file names starting with a tilde (~). If set, it should be set to an absolute file name. (If set to a relative file name, Emacs interprets it relative to the directory where Emacs was started, but we don't recommend to use this feature.) If unset, HOME normally defaults to the home directory of the user given by LOGNAME, USER or your user ID, or to / if all else fails. On MS-DOS, it defaults to the directory from which Emacs was started, with /bin removed from the end if it was present. On Windows, the default value of HOME is the Application Data subdirectory of the user profile directory (normally, this is C:/Documents and Settings//username//Application Data, where username is your user name), though for backwards compatibility C:/ will be used instead if a .emacs file is found there.

HOSTNAME

The name of the machine that Emacs is running on.

INFOPATH

A colon-separated list of directories in which to search for Info files.

LC_ALL, LC_COLLATE, LC_CTYPE, LC_MESSAGES, LC_MONETARY, LC_NUMERIC, LC_TIME, LANG

The user's preferred locale. The locale has six categories, specified by the environment variables LC_COLLATE for sorting, LC_CTYPE for character encoding, LC_MESSAGES for system messages, LC_MONETARY for monetary formats, LC_NUMERIC for numbers, and LC_TIME for dates and times. If one of these variables is not set, the category defaults to the value of the LANG environment variable, or to the default C locale if LANG is not set. But if LC_ALL is specified, it overrides the settings of all the other locale environment variables. On MS-Windows and macOS, if LANG is not already set in the environment, Emacs sets it based on the system-wide default. You can set this in the ``Regional Settings'' Control Panel on some versions of MS-Windows, and in the ``Language and Region'' System Preference on macOS. When running a GUI session on Android, LANG is set to a fixed value, but the language and locale environment is derived from the system's ``Languages & Input'' preferences. Android Environment. The value of the LC_CTYPE category is matched against entries in locale-language-names, locale-charset-language-names, and locale-preferred-coding-systems, to select a default language environment and coding system. Language Environments.

LOGNAME

The user's login name. See also USER.

MAIL

The name of your system mail inbox.

MH

Name of setup file for the mh system. MH-E.

NAME

Your real-world name. This is used to initialize the variable user-full-name (Mail Headers).

NNTPSERVER

The name of the news server. Used by the mh and Gnus packages.

ORGANIZATION

The name of the organization to which you belong. Used for setting the Organization: header in your posts from the Gnus package.

PATH

A colon-separated list of directories containing executable files. This is used to initialize the variable exec-path (Shell).

PWD

If set, this should be the default directory when Emacs was started.

REPLYTO

If set, this specifies an initial value for the variable mail-default-reply-to (Mail Headers).

SAVEDIR

The name of a directory in which news articles are saved by default. Used by the Gnus package.

SHELL

The name of an interpreter used to parse and execute programs run from inside Emacs. This is used to initialize the variable shell-file-name (Single Shell).

SMTPSERVER

The name of the outgoing mail server. This is used to initialize the variable smtpmail-smtp-server (Mail Sending).

TERM

The type of the terminal that Emacs is using. This variable must be set unless Emacs is run in batch mode. On MS-DOS, it defaults to internal, which specifies a built-in terminal emulation that handles the machine's own display.

TERMCAP

The name of the termcap library file describing how to program the terminal specified by TERM. This defaults to /etc/termcap.

TMPDIR, TMP, TEMP

These environment variables are used to initialize the variable temporary-file-directory, which specifies a directory in which to put temporary files (Backup). Emacs tries to use TMPDIR first. If that is unset, Emacs normally falls back on /tmp, but on MS-Windows and MS-DOS it instead falls back on TMP, then TEMP, and finally c:/temp.

TZ

This specifies the default time zone and possibly also daylight saving time information. Time Zone Rules. On MS-DOS, if TZ is not set in the environment when Emacs starts, Emacs defines a default value as appropriate for the country code returned by DOS. On MS-Windows, Emacs does not use TZ at all.

USER

The user's login name. See also LOGNAME. On MS-DOS, this defaults to root.

VERSION_CONTROL

Used to initialize the version-control variable (Backup Names).