Provided by: manpages_6.03-1_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  array  of  strings  is  made
       available  to  the  process  by  the execve(2) call when a new program is started.  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".   The  name  is  case-
       sensitive  and  may  not contain the character "=".  The value can be anything that can be
       represented as a string.  The name and the value may not contain  an  embedded  null  byte
       ('\0'), since this is assumed to terminate the string.

       Environment  variables  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

       What  follows is a list of environment variables typically seen on a system.  This list is
       incomplete and includes only common variables seen by average users  in  their  day-to-day
       routine.   Environment  variables specific to a particular program or library function are
       documented in the ENVIRONMENT section of the appropriate manual page.

       USER   The name of the logged-in user (used by some BSD-derived programs).  Set  at  login
              time, see section NOTES below.

              The  name  of  the logged-in user (used by some System-V derived programs).  Set at
              login time, see section NOTES below.

       HOME   A user's login directory.  Set at login time, see section NOTES below.

       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 employ when
              searching for an executable file that is specified as a simple  filename  (i.a.,  a
              pathname that contains no slashes).  The prefixes are separated by colons (:).  The
              list of prefixes is searched from beginning to end, by checking the pathname formed
              by  concatenating  a  prefix,  a slash, and the filename, until a file with execute
              permission is found.

              As a legacy feature, a zero-length prefix (specified as two adjacent colons, or  an
              initial or terminating colon) is interpreted to mean the current working directory.
              However, use of this feature is deprecated,  and  POSIX  notes  that  a  conforming
              application  shall  use  an  explicit  pathname  (e.g.,  .)  to specify the current
              working directory.

              Analogously to PATH, 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    Absolute  path to the current working directory; required to be partially canonical
              (no . or .. components).

       SHELL  The absolute pathname of the user's login shell.  Set at login  time,  see  section
              NOTES below.

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

       PAGER  The  user's  preferred  utility  to display text files.  Any string acceptable as a
              command-string operand to the sh -c command shall be valid.  If PAGER is null or is
              not  set,  then  applications that launch a pager will default to a program such as
              less(1) or more(1).

              The user's preferred utility to edit  text  files.   Any  string  acceptable  as  a
              command_string operand to the sh -c command shall be valid.

       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.  See also

       •  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).


       Historically and by standard, environ must be declared in the user program.  However, as a
       (nonstandard) programmer convenience, environ is declared in the header file <unistd.h> if
       the _GNU_SOURCE feature test macro is defined (see feature_test_macros(7)).

       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.

       The  HOME,  LOGNAME,  SHELL,  and  USER  variables  are set when the user is changed via a
       session management interface, typically by a program such as login(1) from a user database
       (such  as  passwd(5)).   (Switching  to  the  root  user using su(1) may result in a mixed
       environment where LOGNAME and USER are retained from old user; see the su(1) manual page.)


       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 and
       LESS.  Such usage is considered mistaken, and to be avoided in new programs.


       bash(1),  csh(1),  env(1),  login(1),  printenv(1),  sh(1),  su(1),  tcsh(1),   execve(2),
       clearenv(3),  exec(3),  getenv(3), putenv(3), setenv(3), unsetenv(3), locale(7),,