environ(7)

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'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'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
          as  LC_COLLATE,  LC_CTYPE, LC_MESSAGES, LC_MONETARY, LC_NUMERIC,
          and LC_TIME (see locale(7)  for  further  details  of  the  LC_*
          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 ':'.  (Similarly one
          has CDPATH 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's login shell.

   TERM   The terminal type for which output is to be prepared.

   PAGER  The user's preferred utility to display text files.

   EDITOR/VISUAL
          The user's preferred utility to edit text files.

   Names may be placed in the shell'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'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.
   A random collection:

   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 tmpnam(3) and
   other routines, and the temporary directory used by sort(1)  and  other
   programs.

   LD_LIBRARY_PATH,  LD_PRELOAD  and  other  LD_*  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 and TZDIR 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  and  LINES  tell  applications about the window size, possibly
   overriding the actual size.

   PRINTER or LPDEST may specify the desired printer to use.  See lpr(1).

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 4.09 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/.

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