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

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

SYNOPSIS

DESCRIPTION

BUGS

SEE ALSO