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 .\" This is free documentation; you can redistribute it and/or
6 .\" modify it under the terms of the GNU General Public License as
7 .\" published by the Free Software Foundation; either version 2 of
8 .\" the License, or (at your option) any later version.
10 .\" The GNU General Public License's references to "object code"
11 .\" and "executables" are to be interpreted as the output of any
12 .\" document formatting or typesetting system, including
13 .\" intermediate and printed output.
15 .\" This manual is distributed in the hope that it will be useful,
16 .\" but WITHOUT ANY WARRANTY; without even the implied warranty of
17 .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
18 .\" GNU General Public License for more details.
20 .\" You should have received a copy of the GNU General Public
21 .\" License along with this manual; if not, write to the Free
22 .\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
25 .\" Modified Sun Jul 25 10:45:30 1993 by Rik Faith (faith@cs.unc.edu)
26 .\" Modified Sun Jul 21 21:25:26 1996 by Andries Brouwer (aeb@cwi.nl)
27 .\" Modified Mon Oct 21 17:47:19 1996 by Eric S. Raymond (esr@thyrsus.com)
28 .\" Modified Wed Aug 27 20:28:58 1997 by Nicolás Lichtmaier (nick@debian.org)
29 .\" Modified Mon Sep 21 00:00:26 1998 by Andries Brouwer (aeb@cwi.nl)
30 .\" Modified Wed Jan 24 06:37:24 2001 by Eric S. Raymond (esr@thyrsus.com)
31 .\" Modified Thu Dec 13 23:53:27 2001 by Martin Schulze <joey@infodrom.org>
33 .TH ENVIRON 7 2009-07-25 "Linux" "Linux Programmer's Manual"
35 environ \- user environment
38 .BI "extern char **" environ ;
44 points to an array of pointers to strings called the "environment".
45 The last pointer in this array has the value NULL.
46 (This variable must be declared in the user program,
47 but is declared in the header file
49 in case the header files came from libc4 or libc5, and
50 in case they came from glibc and
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
76 by \fBLC_ALL\fP or more specific environment variables like
77 \fBLC_COLLATE\fP, \fBLC_CTYPE\fP, \fBLC_MESSAGES\fP, \fBLC_MONETARY\fP,
78 \fBLC_NUMERIC\fP, \fBLC_TIME\fP, cf.
82 The sequence of directory prefixes that
85 programs apply in searching for a file known by an incomplete pathname.
86 The prefixes are separated by \(aq\fB:\fP\(aq.
87 (Similarly one has \fBCDPATH\fP used by some shells to find the target
88 of a change directory command, \fBMANPATH\fP used by
91 find manual pages, etc.)
94 The current working directory.
98 The pathname of the user's login shell.
101 The terminal type for which output is to be prepared.
104 The user's preferred utility to display text files.
107 The user's preferred utility to edit text files.
110 .\" The user's preferred utility to browse URLs. Sequence of colon-separated
111 .\" browser commands. See http://www.catb.org/~esr/BROWSER/ .
113 Further names may be placed in the environment by the \fIexport\fP
114 command and "name=value" in
116 or by the \fIsetenv\fP command if you use
118 Arguments may also be placed in the
119 environment at the point of an
121 A C program can manipulate its environment using the functions
128 Note that the behavior of many programs and library routines is
129 influenced by the presence or value of certain environment variables.
133 .BR LANG ", " LANGUAGE ", " NLSPATH ", " LOCPATH ", "
134 .BR LC_ALL ", " LC_MESSAGES ", "
135 etc. influence locale handling, cf.
139 influences the path prefix of names created by
141 and other routines, the temporary directory used by
143 and other programs, etc.
145 .BR LD_LIBRARY_PATH ", " LD_PRELOAD
146 and other LD_* variables influence
147 the behavior of the dynamic loader/linker.
150 makes certain programs and library routines follow
151 the prescriptions of POSIX.
161 gives the name of a file containing aliases
163 .BR gethostbyname (3).
166 give timezone information used by
168 and through that by functions like
177 gives information on how to address a given terminal
178 (or gives the name of a file containing such information).
180 .BR COLUMNS " and " LINES
181 tell applications about the window size, possibly overriding the actual size.
183 .BR PRINTER " or " LPDEST
184 may specify the desired printer to use.
190 Clearly there is a security risk here.
191 Many a system command has been
192 tricked into mischief by a user who specified unusual values for
193 .BR IFS " or " LD_LIBRARY_PATH .
195 There is also the risk of name space pollution.
200 allow overriding of default utility names from the
201 environment with similarly named variables in all caps.
204 to select the desired C compiler (and similarly
214 However, in some traditional uses such an environment variable
215 gives options for the program instead of a pathname.
221 Such usage is considered mistaken, and to be avoided in new
225 should consider renaming their option to