1 .\" Copyright (c) 1993 Michael Haardt (michael@moria.de),
2 .\" Fri Apr 2 11:32:09 MET DST 1993
3 .\" and Andries Brouwer (aeb@cwi.nl), Fri Feb 14 21:47:50 1997.
5 .\" %%%LICENSE_START(GPLv2+_DOC_FULL)
6 .\" This is free documentation; you can redistribute it and/or
7 .\" modify it under the terms of the GNU General Public License as
8 .\" published by the Free Software Foundation; either version 2 of
9 .\" the License, or (at your option) any later version.
11 .\" The GNU General Public License's references to "object code"
12 .\" and "executables" are to be interpreted as the output of any
13 .\" document formatting or typesetting system, including
14 .\" intermediate and printed output.
16 .\" This manual is distributed in the hope that it will be useful,
17 .\" but WITHOUT ANY WARRANTY; without even the implied warranty of
18 .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 .\" GNU General Public License for more details.
21 .\" You should have received a copy of the GNU General Public
22 .\" License along with this manual; if not, see
23 .\" <http://www.gnu.org/licenses/>.
26 .\" Modified Sun Jul 25 10:45:30 1993 by Rik Faith (faith@cs.unc.edu)
27 .\" Modified Sun Jul 21 21:25:26 1996 by Andries Brouwer (aeb@cwi.nl)
28 .\" Modified Mon Oct 21 17:47:19 1996 by Eric S. Raymond (esr@thyrsus.com)
29 .\" Modified Wed Aug 27 20:28:58 1997 by Nicolás Lichtmaier (nick@debian.org)
30 .\" Modified Mon Sep 21 00:00:26 1998 by Andries Brouwer (aeb@cwi.nl)
31 .\" Modified Wed Jan 24 06:37:24 2001 by Eric S. Raymond (esr@thyrsus.com)
32 .\" Modified Thu Dec 13 23:53:27 2001 by Martin Schulze <joey@infodrom.org>
34 .TH ENVIRON 7 2014-08-19 "Linux" "Linux Programmer's Manual"
36 environ \- user environment
39 .BI "extern char **" environ ;
45 points to an array of pointers to strings called the "environment".
46 The last pointer in this array has the value NULL.
47 (This variable must be declared in the user program,
48 but is declared in the header file
52 feature test macro is defined.)
53 This array of strings is made available to the process by the
55 call that started the process.
57 By convention the strings in
59 have the form "\fIname\fP\fB=\fP\fIvalue\fP".
63 The name of the logged-in user (used by some BSD-derived programs).
66 The name of the logged-in user (used by some System-V derived programs).
69 A user's login directory, set by
71 from the password file
75 The name of a locale to use for locale categories when not overridden
78 or more specific environment variables such as
88 for further details of the
90 environment variables).
93 The sequence of directory prefixes that
96 programs apply in searching for a file known by an incomplete pathname.
97 The prefixes are separated by \(aq\fB:\fP\(aq.
100 used by some shells to find the target
101 of a change directory command,
105 to find manual pages, and so on)
108 The current working directory.
112 The pathname of the user's login shell.
115 The terminal type for which output is to be prepared.
118 The user's preferred utility to display text files.
121 The user's preferred utility to edit text files.
124 .\" The user's preferred utility to browse URLs. Sequence of colon-separated
125 .\" browser commands. See http://www.catb.org/~esr/BROWSER/ .
127 Further names may be placed in the environment by the
129 command and "name=value" in
135 Arguments may also be placed in the
136 environment at the point of an
138 A C program can manipulate its environment using the functions
145 Note that the behavior of many programs and library routines is
146 influenced by the presence or value of certain environment variables.
150 .BR LANG ", " LANGUAGE ", " NLSPATH ", " LOCPATH ", "
151 .BR LC_ALL ", " LC_MESSAGES ", "
152 and so on influence locale handling; see
159 influences the path prefix of names created by
161 and other routines, and the temporary directory used by
165 .BR LD_LIBRARY_PATH ", " LD_PRELOAD
166 and other LD_* variables influence
167 the behavior of the dynamic loader/linker.
170 makes certain programs and library routines follow
171 the prescriptions of POSIX.
181 gives the name of a file containing aliases
183 .BR gethostbyname (3).
186 give timezone information used by
188 and through that by functions like
197 gives information on how to address a given terminal
198 (or gives the name of a file containing such information).
200 .BR COLUMNS " and " LINES
201 tell applications about the window size, possibly overriding the actual size.
203 .BR PRINTER " or " LPDEST
204 may specify the desired printer to use.
210 Clearly there is a security risk here.
211 Many a system command has been
212 tricked into mischief by a user who specified unusual values for
213 .BR IFS " or " LD_LIBRARY_PATH .
215 There is also the risk of name space pollution.
220 allow overriding of default utility names from the
221 environment with similarly named variables in all caps.
224 to select the desired C compiler (and similarly
234 However, in some traditional uses such an environment variable
235 gives options for the program instead of a pathname.
241 Such usage is considered mistaken, and to be avoided in new
245 should consider renaming their option to