A crude, simple means of InterProcessCommunication, often used for trivial configuration needs.

AddToMe: inherited by child processes, cannot be changed at runtime from outside process, etc.

Invoke printenv(1) to print a list of the current values of all the EnvironmentVariables in the invoking process.

Since make(1) often uses EnvironmentVariables named after commands to store the path to command in question, such names should be avoided for other purposes. Examples include CC, BISON, YACC, LEX, FLEX, F77, LD etc. It also uses the FLAGS suffix for default flags to pass a command, eg: CFLAGS, LDFLAGS, etc.

A list of environment variables consulted by commonly used programs, libraries etc

No claims as to comprehensiveness or correctness made.

APT_CONFIG

see apt.conf(5)

ASPELL_CONF

Configuration file for aspell, see aspell(1)

BROWSER

The user's prefered browser (see The BROWSER project)

BZCAT

Command line arguments for bzcat

BZIP2

Command line arguments for BZIP2

COLUMNS

Number of columns on the screen

DEAD

used by Mail(1) apparently.

DISPLAY

Current X(1) display

EDITOR

Users prefered program to edit text files

ftp_proxy

ftp proxy server, used by various programs (eg see apt.conf(5), lynx(1), wget(1), ...)

HOME

Home directory

HOSTALIASES

Path to host aliases file, see hostname(7).

HOSTFILE

Path to /etc/hosts

http_proxy

http proxy server, used by various programs (eg see apt.conf(5), lynx(1), wget(1), ...)

HZ

Kernel timer mechanism

IFS

Internal Field Seperator, used for word splitting in shells, see bash(1)

INPUTRC

Path to .inputrc file. see bash(1)

LANG

The name of the locale to use for locale categories. See locale(5)

LC_ADDRESS

Locale settings, see locale(1)

LC_ALL

Locale settings, see locale(1)

LC_COLLATE

Locale settings, see locale(1)

LC_CTYPE

Locale settings, see locale(1)

LC_IDENTIFICATION

Locale settings, see locale(1)

LC_MEASUREMENT

Locale settings, see locale(1)

LC_MESSAGES

Locale settings, see locale(1)

LC_MONETARY

Locale settings, see locale(1)

LC_NAME

Locale settings, see locale(1)

LC_NUMERIC

Locale settings, see locale(1)

LC_PAPER

Locale Paper size, see locale(1)

LC_TELEPHONE

Locale settings, see locale(1)

LD_AOUT_LIBRARY_PATH

LD_LIBRARY_PATH for a.out binaries

LD_AOUT_PRELOAD

LD_PRELOAD for a.out binaries

LD_ASSUME_KERNEL

used to control the choice of threading implementation by pthreads(7)?, and other things as well.

LD_BIND_NOW

Disable lazy linking, see ld.so(8)

LD_KEEPDIR

Don't ignore directory names of a.out libraries. see ld.so(8)

LD_LIBRARY_PATH

Path to search for libraries, see ld.so(8)

LD_NOWARN

Suppress warnings of a.out minor version differences, see ld.so(8)

LD_PRELOAD

Libraries to load before all others, see ld.so(8)

LD_TRACE_LOADED_OBJECTS

Give ldd output instead of running, see ld.so(8)

LESSANSIENDCHARS

see less(1)

LESSBINFMT

see less(1)

LESSCHARDEF

Charset definition for less(1)

LESSCHARSET

Charset used by less(1) to display.

LESSCLOSE

see less(1)

LESSECHO

see less(1)

LESSEDIT

Editor used by less(1)

LESSGLOBALTAGS

see less(1)

LESSKEY

Name of the lesskey(1) file

LESSKEY_SYSTEM

Name of the system wide lesskey(1) file

LESSMETAESCAPE

see less(1)

LESSOPEN

less(1) preprocessor

LESS

options passed to less(1) automatically

LESSSECURE

Put less(1) into secure mode.

LESSSEPERATOR

used by less(1)

LINES

Number of lines on the screen

LISTER

Used by Mail(1), obsolete version of PAGER?

LOCALDOMAIN

Local domain, see hostname(7)

LOGNAME

The name of the logged in user

LPDEST

Default printer

MAILCHECK

How often to check for mail (in seconds), see bash(1)

MAIL

File for the shell to check for mail, see bash(1)

MAILPATH

Files for the shell to check for mail, see bash(1)

MALLOC_CHECK_

Change the implementation of malloc(3) to catch more bugs.

MANPATH

Path to search for man pages

MBOX

Path to mbox file? see Mail(1)

NGPRNTER

Default printer, see lpr(1)

NPRINTER

Default printer, see lpr(1)

PAGER

The user's prefered pager program

PATH

Path to search for programs

POSIXLY_CORRECT

Makes programs/libraries adhere to strict POSIX requirements.

PRINTER

Default printer

PROMPT_COMMAND

Command for the shell to run every time it displays a prompt, see bash(1)

PS1

Shell prompt; see bash(1), particularly the PROMPTING section for info on how to change the shell prompt.
PS1='\e[31m\A\e[0m \u@\h:\w>' looks quite nice :)

PS2

Secondary Shell prompt, displayed when a previous line continues; see bash(1). (You will see this prompt if you forget to close a quote.)

PS3

Shell prompt, see bash(1)

PS4

Shell prompt, see bash(1)

PWD

Process Working Directory (set by some shells)

REPLYTO

Used by Mail(1), reply to address?

RESOLV_ADD_TRIM_DOMAINS

Adds to Trim Domains, see resolv+(8)

RESOLV_HOST_CONF

Filename of /etc/host.conf. see resolv+(8), host.conf(5)

RESOLV_MULTI

Overrides "multi" keyword from /etc/host.conf, see resolv+(8)

RESOLV_OVERRIDE_TRIM_DOMAINS

Overrides Tirm Domains from /etc/host.conf, see resolv+(8)

RESOLV_REORDER

Overrides the "reorder" keyword from /etc/host.conf, see resolv+(8)

RESOLV_SERV_ORDER

Overrides "order" keyword in /etc/host.conf, see resolv+(8)

RESOLV_SPOOF_CHECK

Sets Spoof Checking see resolv+(8)

SHELL

The user's shell

SSH_ASKPASS

Used by ssh(1)

SSH_AUTH_SOCK

Used by ssh(1)

SSH_CLIENT

Used by ssh(1)

SSH_ORIGINAL_COMMAND

Used by ssh(1)

SSH_TTY

Used by ssh(1)

SYSTEM

Operating System, used by apropos(1)

TERMCAP

Terminal type capabilities file

TERM

The terminal type

TIMEFORMAT

format of the time(1) command, see time(1) and bash(1)

TMOUT

Timeout for shells to log you out, see bash(1)

TMPDIR

Directory for temp files, see tempnam(3), sort(1) etc See PerUserTempDirs

TZDIR

Set TimeZone information

TZ

Set TimeZone information, tzset(1)?

USER

The currently logged in user

VISUAL

The user's prefered visual editor