Section (7) environ
Name
environ — user environment
Synopsis
extern char **environ;
DESCRIPTION
The variable 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
header file <
unistd.h
>
if 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
parent_zsingle_quotesz_s environment.
By convention the strings in environ
have the form
name
=
value
. Common examples
are:
USER
-
The name of the logged-in user (used by some BSD-derived programs).
LOGNAME
-
The name of the logged-in user (used by some System-V derived programs).
HOME
-
A user_zsingle_quotesz_s login directory, set by login(1) from the password file passwd(5).
LANG
-
The name of a locale to use for locale categories when not overridden by
LC_ALL
or more specific environment variables such asLC_COLLATE
,LC_CTYPE
,LC_MESSAGES
,LC_MONETARY
,LC_NUMERIC
, andLC_TIME
(see locale(7) for further details of theLC_*
environment variables). PATH
-
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 _zsingle_quotesz_
:
_zsingle_quotesz_. (Similarly one hasCDPATH
used by some shells to find the target of a change directory command,MANPATH
used by man(1) to find manual pages, and so on) PWD
-
The current working directory. Set by some shells.
SHELL
-
The pathname of the user_zsingle_quotesz_s login shell.
TERM
-
The terminal type for which output is to be prepared.
PAGER
-
The user_zsingle_quotesz_s preferred utility to display text files.
EDITOR
/VISUAL
-
The user_zsingle_quotesz_s preferred utility to edit text files.
Names may be placed in the shell_zsingle_quotesz_s environment by the
export
command in
sh(1), or by the setenv command if you use
csh(1).
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_zsingle_quotesz_s environment; see the manual page of
your preferred shell for details.
Bourne-style shells support the syntax
NAME=value command
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 command
.
Arguments may also be placed in the environment at the point of an exec(3). A C program can manipulate its environment using the functions getenv(3), putenv(3), setenv(3), and unsetenv(3).
Note that the behavior of many programs and library routines is influenced by the presence or value of certain environment variables. Examples include the following:
-
The variables
LANG
,LANGUAGE
,NLSPATH
,LOCPATH
,LC_ALL
,LC_MESSAGES
, and so on influence locale handling; see catopen(3), gettext(3), and locale(7). -
TMPDIR
influences the path prefix of names created by tempnam(3) and other routines, and the temporary directory used by sort(1) and other programs. -
LD_LIBRARY_PATH
,LD_PRELOAD
, and otherLD_*
variables influence the behavior of the dynamic loader/linker. -
POSIXLY_CORRECT
makes certain programs and library routines follow the prescriptions of POSIX. -
The behavior of malloc(3) is influenced by
MALLOC_*
variables. -
The variable
HOSTALIASES
gives the name of a file containing aliases to be used with gethostbyname(3). -
TZ
andTZDIR
give timezone information used by tzset(3) and through that by functions like ctime(3), localtime(3), mktime(3), strftime(3). See also tzselect(8). -
TERMCAP
gives information on how to address a given terminal (or gives the name of a file containing such information). -
COLUMNS
andLINES
tell applications about the window size, possibly overriding the actual size. -
PRINTER
orLPDEST
may specify the desired printer to use. See lpr(1).
NOTES
The prctl(2) PR_SET_MM_ENV_START
and PR_SET_MM_ENV_END
operations can be used to
control the location of the process_zsingle_quotesz_s environment.
BUGS
Clearly there is a security risk here. Many a system
command has been tricked into mischief by a user who
specified unusual values for IFS
or LD_LIBRARY_PATH
.
There is also the risk of name space pollution. Programs
like make
and
autoconf
allow
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 MAKE
,
AR
, AS
, FC
,
LD
, LEX
, RM
,
YACC
, etc.). However, in some
traditional uses such an environment variable gives options
for the program instead of a pathname. Thus, one has
MORE
, LESS
, and GZIP
. Such usage is considered mistaken,
and to be avoided in new programs. The authors of gzip
should consider renaming
their option to GZIP_OPT
.
SEE ALSO
bash(1), csh(1), env(1), login(1), printenv(1), sh(1), tcsh(1), execve(2), clearenv(3), exec(3), getenv(3), putenv(3), setenv(3), unsetenv(3), locale(7), ld.so(8), pam_env(8)
COLOPHON
This page is part of release 4.16 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
https://www.kernel.org/doc/man−pages/.
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. %%%LICENSE_START(GPLv2+_DOC_FULL) 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_zsingle_quotesz_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 <http://www.gnu.org/licenses/>. %%%LICENSE_END 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> |