Provided by: manpages_5.05-1_all bug


       environ - user environment


       extern char **environ;


       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).

              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.

              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

       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

       Note that the behavior of many programs and library routines is influenced by the presence
       or value of certain environment variables.  Examples include the following:

       *  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 tempnam(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

       *  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

       *  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).


       The  prctl(2)  PR_SET_MM_ENV_START and PR_SET_MM_ENV_END operations can be used to control
       the location of the process's environment.


       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.


       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),, pam_env(8)


       This page is part of release 5.05 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