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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> in case the header files came from libc4  or
       libc5,  and  in case they came from glibc and _GNU_SOURCE was defined.)
       This array of strings is made available to the process by  the  exec(3)
       call that started the process.

       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.

       Further names may be placed in the environment by  the  export  command
       and  "name=value" in sh(1), or by the setenv command if you use csh(1).
       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).

       Etc.

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),  login(1),  sh(1),  tcsh(1),  execve(2), clearenv(3),
       exec(3), getenv(3), putenv(3), setenv(3), unsetenv(3), locale(7)

COLOPHON

       This page is part of release 3.65 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.



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