environ(7)

1ENVIRON(7)                 Linux Programmer's Manual                ENVIRON(7)
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NAME

6       environ - user environment
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SYNOPSIS

9       extern char **environ;
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DESCRIPTION

12       The  variable  environ points to an array of pointers to strings called
13       the "environment".  The last pointer in this array has the value  NULL.
14       (This variable must be declared in the user program, but is declared in
15       the header file <unistd.h> in case the header files came from libc4  or
16       libc5,  and  in case they came from glibc and _GNU_SOURCE was defined.)
17       This array of strings is made available to the process by  the  exec(3)
18       call that started the process.
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20       By  convention the strings in environ have the form "name=value".  Com‐
21       mon examples are:
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23       USER   The name of the logged-in user (used by  some  BSD-derived  pro‐
24              grams).
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26       LOGNAME
27              The  name  of  the logged-in user (used by some System-V derived
28              programs).
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30       HOME   A user's login directory, set by login(1) from the password file
31              passwd(5).
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33       LANG   The name of a locale to use for locale categories when not over‐
34              ridden by LC_ALL or more  specific  environment  variables  like
35              LC_COLLATE,   LC_CTYPE,  LC_MESSAGES,  LC_MONETARY,  LC_NUMERIC,
36              LC_TIME, cf.  locale(5).
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38       PATH   The sequence of directory prefixes that  sh(1)  and  many  other
39              programs  apply  in  searching for a file known by an incomplete
40              pathname.  The prefixes are separated by  ':'.   (Similarly  one
41              has  CDPATH  used  by some shells to find the target of a change
42              directory command, MANPATH used by man(1) to find manual  pages,
43              etc.)
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45       PWD    The current working directory.  Set by some shells.
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47       SHELL  The pathname of the user's login shell.
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49       TERM   The terminal type for which output is to be prepared.
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51       PAGER  The user's preferred utility to display text files.
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53       EDITOR/VISUAL
54              The user's preferred utility to edit text files.
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56       Further  names  may  be placed in the environment by the export command
57       and "name=value" in sh(1), or by the setenv command if you use  csh(1).
58       Arguments  may  also  be  placed  in the environment at the point of an
59       exec(3).  A C program can manipulate its environment  using  the  func‐
60       tions getenv(3), putenv(3), setenv(3), and unsetenv(3).
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62       Note  that the behavior of many programs and library routines is influ‐
63       enced by the presence or value of  certain  environment  variables.   A
64       random collection:
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66       The  variables  LANG,  LANGUAGE, NLSPATH, LOCPATH, LC_ALL, LC_MESSAGES,
67       etc. influence locale handling, cf.  locale(5).
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69       TMPDIR influences the path prefix of names  created  by  tmpnam(3)  and
70       other  routines, the temporary directory used by sort(1) and other pro‐
71       grams, etc.
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73       LD_LIBRARY_PATH, LD_PRELOAD and  other  LD_*  variables  influence  the
74       behavior of the dynamic loader/linker.
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76       POSIXLY_CORRECT  makes certain programs and library routines follow the
77       prescriptions of POSIX.
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79       The behavior of malloc(3) is influenced by MALLOC_* variables.
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81       The variable HOSTALIASES gives the name of a file containing aliases to
82       be used with gethostbyname(3).
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84       TZ  and  TZDIR  give  timezone information used by tzset(3) and through
85       that by functions like ctime(3), localtime(3), mktime(3),  strftime(3).
86       See also tzselect(8).
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88       TERMCAP  gives information on how to address a given terminal (or gives
89       the name of a file containing such information).
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91       COLUMNS and LINES tell applications about  the  window  size,  possibly
92       overriding the actual size.
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94       PRINTER or LPDEST may specify the desired printer to use.  See lpr(1).
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96       Etc.
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BUGS

99       Clearly  there is a security risk here.  Many a system command has been
100       tricked into mischief by a user who specified unusual values for IFS or
101       LD_LIBRARY_PATH.
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103       There is also the risk of name space pollution.  Programs like make and
104       autoconf allow overriding of default utility names from the environment
105       with similarly named variables in all caps.  Thus one uses CC to select
106       the desired C compiler (and similarly MAKE, AR, AS, FC,  LD,  LEX,  RM,
107       YACC,  etc.).   However,  in  some traditional uses such an environment
108       variable gives options for the program instead of  a  pathname.   Thus,
109       one  has  MORE, LESS, and GZIP.  Such usage is considered mistaken, and
110       to be avoided in new programs.  The authors  of  gzip  should  consider
111       renaming their option to GZIP_OPT.
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COLOPHON

118       This page is part of release 3.25 of the Linux  man-pages  project.   A
119       description  of  the project, and information about reporting bugs, can
120       be found at http://www.kernel.org/doc/man-pages/.
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124Linux                             2009-07-25                        ENVIRON(7)

NAME

SYNOPSIS

DESCRIPTION

BUGS

SEE ALSO

COLOPHON