4.3BSD-Tahoe/usr/src/man/man7/environ.7

.\" Copyright (c) 1983 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
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.\"	@(#)environ.7	6.4 (Berkeley) 10/14/87
.\"
.TH ENVIRON 7 "October 14, 1987"
.UC 5
.SH NAME
environ \- user environment
.SH SYNOPSIS
.B extern char **environ;
.SH DESCRIPTION
An array of strings called the
.I environment
is made available by
.IR execve (2)
when a process begins.  By convention these strings have the form
``\fIname=value\fP''.  The following names are used by various commands:
.TP "\w'TERMPATH 'u"
EXINIT
A startup list of commands read by
.IR ex (1),
.IR edit (1),
and
.IR vi (1).
.TP
HOME
A user's login directory, set by
.IR login (1)
from the password file
.IR passwd (5).
.TP
PATH
The sequence of directories, separated by colons, searched by
.IR csh (1),
.IR sh (1),
.IR system (3),
.IR execvp (3),
etc, when looking for an executable file.
PATH is set to ``:/usr/ucb:/bin:/usr/bin'' initially by
.IR login (1).
.TP
PRINTER
The name of the default printer to be used by
.IR lpr (1),
.IR lpq (1),
and
.IR lprm (1).
.TP
SHELL
The full pathname of the user's login shell.
.TP
TERM
The kind of terminal for which output is to be prepared.
This information is used by commands, such as
.IR nroff (1)
or
.IR plot (1G),
which may exploit special terminal capabilities.  See
.I /etc/termcap
.RI ( termcap (5))
for a list of terminal types.
.TP
TERMCAP
The string describing the terminal in TERM, or, if
it begins with a '/', the name of the termcap file.
See TERMPATH below, 
.IR termcap (5),
and
.IR termcap (3X).
.TP
TERMPATH
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.
.TP
USER
The login name of the user.
.PP
Further names may be placed in the environment by the
.I export
command and
.IR name = value
arguments in
.IR sh (1),
or by the
.I setenv
command if you use
.IR csh (1).
It is unwise to change certain 
.IR sh (1)
variables that are frequently exported by
.I .profile
files, such as MAIL, PS1, PS2, and IFS,
unless you know what you are doing.
.SH SEE ALSO
csh(1), ex(1), login(1), sh(1), execve(2), execle(3),
system(3), termcap(3), termcap(5)