• NAME
  
  environ - user environment
• SYNOPSIS
  

  
   extern char ** environ ;
  
   
  
  

• DESCRIPTION
  
  The variable
  environ
  points to an array of strings called the "environment".
  (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 these strings
  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 like
  LC_COLLATE, LC_CTYPE, LC_MESSAGES, LC_MONETARY,
  LC_NUMERIC, LC_TIME, cf.
  locale(5) .
  

  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 (aq:(aq.
  (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, etc.)
  

  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 ", "
  etc. influence locale handling, cf.
  locale(5) .
  
  TMPDIR influences the path prefix of names created by
  tmpnam(3)
  and other routines, the temporary directory used by
  sort(1)
  and other programs, etc.
  
  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(5)
  
• COLOPHON
  
  This page is part of release 3.19 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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