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ENVIRON Section: Linux Programmer's Manual (5) Updated: October 21, 2025 Index   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 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 LANG The name of a locale to use for locale categories when not overridden by LC_ALL or more specific environment variables. PATH programs apply in searching for a file known by an incomplete path name. The prefixes are separated by `:'. (Similarly one has CDPATH used by some shells to find the target find manual pages, etc.) PWD The current working directory. Set by some shells. SHELL The file name of the user's login shell. TERM The terminal type for which output is to be prepared. Further names may be placed in the environment by the export A C program can manipulate its environment using the functions getenv(), putenv(), setenv() and unsetenv(). Note that the behaviour 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. TMPDIR influences the path prefix of names created by tmpnam() and other routines, the temporary directory used by LD_LIBRARY_PATH, LD_PRELOAD and other LD_* variables influence the behaviour of the dynamic loader/linker. POSIXLY_CORRECT makes certain programs and library routines follow the prescriptions of POSIX. The behaviour of malloc() is influenced by MALLOC_* variables. The variable HOSTALIASES gives the name of a file containing aliases to be used with gethostbyname(). TZ and TZDIR give time zone information. TERMCAP gives information on how to address a given terminal (or gives the name of a file containing such information). Etc. etc. 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.   SEE ALSO   Index NAME SYNOPSIS DESCRIPTION SEE ALSO This document was created by using the manual pages. Time: 12:12:24 GMT, March 24, 2025

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