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ENVIRON(7) Miscellaneous Information Manual ENVIRON(7)

environ — user environment

extern char **environ;

An array of strings called the environment is made available by execve(2) when a process begins. By convention these strings have the form “name=value”. The following names are used by various commands:

The size of the block units used by several commands, most notably df(1), du(1) and ls(1). This variable is processed by the getbsize(3) function.
The user's preferred width in column positions for the terminal. Utilities such as ls(1) and who(1) use this to format output into columns. If unset or empty, utilities will use an ioctl(2) call to ask the terminal driver for the width.
Default editor name.
A startup list of commands read by ex(1) and vi(1).
A user's login directory, set by login(1) from the password file passwd(5).
This variable configures all programs which use setlocale(3) to use the specified locale unless the LC_* variables are set.
Overrides the values of LC_COLLATE, LC_CTYPE, LC_MESSAGES, LC_MONETARY, LC_NUMERIC, LC_TIME and LANG.
Locale to be used for ordering of strings.
Locale to be used for character classification (letter, space, digit, etc.) and for interpreting byte sequences as multibyte characters.
Locale to be used for diagnostic messages.
Locale to be used for interpreting monetary input and formatting output.
Locale to be used for interpreting numeric input and formatting output.
Locale to be used for interpreting dates input and for formatting output.
The location of the user's mailbox instead of the default in /var/mail, used by mail(1), sh(1), and many other mail clients.
List of directories to be searched for the message catalog referred to by LC_MESSAGES. See catopen(3).
Default paginator program. The program specified by this variable is used by mail(1), man(1), ftp(1), etc, to display information which is longer than the current display.
The sequence of directories, separated by colons, searched by csh(1), sh(1), system(3), execvp(3), etc, when looking for an executable file. PATH is set to ``/usr/bin:/bin'' initially by login(1).
The name of the default printer to be used by lpr(1), lpq(1), and lprm(1).
The current directory pathname.
The full pathname of the user's login shell.
The kind of terminal for which output is to be prepared. This information is used by commands, such as nroff(1) or plot(1) which may exploit special terminal capabilities. See /usr/share/misc/termcap (termcap(5)) for a list of terminal types.
The string describing the terminal in TERM, or, if it begins with a '/', the name of the termcap file. See TERMPATH below, and termcap(5).
A sequence of pathnames of termcap files, separated by colons or spaces, which are searched for terminal descriptions in the order listed. Having no TERMPATH is equivalent to a TERMPATH of “$HOME/.termcap:/etc/termcap”. TERMPATH is ignored if TERMCAP contains a full pathname.
The directory in which to store temporary files. Most applications use either “/tmp” or “/var/tmp”. Setting this variable will make them use another directory.
The timezone to use when displaying dates. The normal format is a pathname relative to “/usr/share/zoneinfo”. For example, the command “env TZ=America/Los_Angeles date” displays the current time in California. See tzset(3) for more information.
The login name of the user.

Further names may be placed in the environment by the export command and name=value arguments in sh(1), or by the setenv command if you use csh(1). It is unwise to change certain sh(1) variables that are frequently exported by .profile files, such as MAIL, PS1, PS2, and IFS, unless you know what you are doing.

The current environment variables can be printed with env(1), set(1) or printenv(1) in sh(1) and env(1), printenv(1) or the printenv built-in command in csh(1).

Programs can query and modify the environment, using the environment routines getenv(3), putenv(3), setenv(3) and unsetenv(3). Direct access can be made through the global variable environ, though it is recommended that changes to the enviroment still be made through the environment routines.

Shared libraries and bundles don't have direct access to environ, which is only available to the loader ld(1) when a complete program is being linked. The environment routines can still be used, but if direct access to environ is needed, the () routine, defined in <crt_externs.h>, can be used to retrieve the address of environ at runtime.

cd(1), csh(1), env(1), ex(1), login(1), printenv(1), sh(1), execve(2), execle(3), getenv(3), putenv(3), setenv(3), unsetenv(3), setlocale(3), system(3), termcap(3), termcap(5)

The environ manual page appeared in 4.2BSD.

April 12, 2003 macOS