environ — user environment
extern char **environ;
environ points to an array of
pointers to strings called the "environment". The last
pointer in this array has the value NULL. (This variable must
be declared in the user program, but is declared in the
_GNU_SOURCE feature test
macro is defined.) This array of strings is made available to
the process by the exec(3) call that started
the process. When a child process is created via fork(2), it inherits a
copy of its
By convention the strings in
environ have the form
value". Common examples
The name of the logged-in user (used by some BSD-derived programs).
The name of the logged-in user (used by some System-V derived programs).
The name of a locale to use for locale categories
when not overridden by
LC_ALL or more specific environment
variables such as
LC_TIME (see locale(7) for further
details of the
The sequence of directory prefixes that sh(1) and many other
programs apply in searching for a file known by an
incomplete pathname. The prefixes are separated by
:'. (Similarly one has
CDPATH used by some
shells to find the target of a change directory
MANPATH used by
man(1) to find manual
pages, and so on)
The current working directory. Set by some shells.
The pathname of the user's login shell.
The terminal type for which output is to be prepared.
The user's preferred utility to display text files.
The user's preferred utility to edit text files.
Names may be placed in the shell's environment by the
export command in
sh(1), or by the setenv command if you use
The initial environment of the shell is populated in
various ways, such as definitions from
/etc/environment that are processed by
pam_env(8) for all users at
login time (on systems that employ pam(8)). In addition,
various shell initialization scripts, such as the system-wide
/etc/profile script and
per-user initializations script may include commands that add
variables to the shell's environment; see the manual page of
your preferred shell for details.
Bourne-style shells support the syntax
to create an environment variable definition only in the
scope of the process that executes
command. Multiple variable
definitions, separated by white space, may precede
Note that the behavior of many programs and library routines is influenced by the presence or value of certain environment variables. A random collection:
LD_PRELOAD and other LD_*
variables influence the behavior of the dynamic
certain programs and library routines follow the
prescriptions of POSIX.
The behavior of malloc(3) is influenced by
gives the name of a file containing aliases to be used with
TERMCAP gives information on
how to address a given terminal (or gives the name of a file
containing such information).
LINES tell applications about the window
size, possibly overriding the actual size.
LPDEST may specify the desired printer to
use. See lpr(1).
Clearly there is a security risk here. Many a system
command has been tricked into mischief by a user who
specified unusual values for
There is also the risk of name space pollution. Programs
overriding of default utility names from the environment with
similarly named variables in all caps. Thus one uses
CC to select the desired C
compiler (and similarly
YACC, etc.). However, in some
traditional uses such an environment variable gives options
for the program instead of a pathname. Thus, one has
GZIP. Such usage is considered mistaken,
and to be avoided in new programs. The authors of
gzip should consider renaming
their option to
This page is part of release 4.07 of the Linux
man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
Copyright (c) 1993 Michael Haardt (michaelmoria.de),
Fri Apr 2 11:32:09 MET DST 1993
and Andries Brouwer (aebcwi.nl), Fri Feb 14 21:47:50 1997.
This is free documentation; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of
the License, or (at your option) any later version.
The GNU General Public License's references to "object code"
and "executables" are to be interpreted as the output of any
document formatting or typesetting system, including
intermediate and printed output.
This manual is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public
License along with this manual; if not, see
Modified Sun Jul 25 10:45:30 1993 by Rik Faith (faithcs.unc.edu)
Modified Sun Jul 21 21:25:26 1996 by Andries Brouwer (aebcwi.nl)
Modified Mon Oct 21 17:47:19 1996 by Eric S. Raymond (esrthyrsus.com)
Modified Wed Aug 27 20:28:58 1997 by Nicolás Lichtmaier (nickdebian.org)
Modified Mon Sep 21 00:00:26 1998 by Andries Brouwer (aebcwi.nl)
Modified Wed Jan 24 06:37:24 2001 by Eric S. Raymond (esrthyrsus.com)
Modified Thu Dec 13 23:53:27 2001 by Martin Schulze <joeyinfodrom.org>