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ENVIRON(7) | Linux Programmer's Manual | ENVIRON(7) |
NAME¶
environ - user environmentSYNOPSIS¶
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> 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. 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).
- 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.
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¶
env(1), bash(1), csh(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), ld.so(8)COLOPHON¶
This page is part of release 3.74 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 http://www.kernel.org/doc/man-pages/.2014-08-19 | Linux |