.TH ENVIRON 5
.UC
.SH NAME
environ \- user environment
.SH SYNOPSIS
.B extern char **environ;
.SH DESCRIPTION
An array of strings called the `environment' is made available by
.IR execve (2)
when a process begins.  By convention these strings have the form
.RI ` name = value '.
The following names are used by various commands:
.TP "\w'TERMCAP 'u"
PATH
The sequence of directory prefixes that
.I sh, time,
.IR nice (1),
etc., apply in searching for a file known by an incomplete path name.
The prefixes are separated by `:'.
.IR Login (1)
sets PATH=:/bin:/usr/ucb:/usr/bin.
.TP
HOME
A user's login directory, set by
.IR login (1)
from the password file
.IR passwd (5).
.TP
SHELL
The name of the user's login shell, set by
.IR login (1)
from the password file
.IR passwd (5).
.TP
TERM
The kind of terminal for which output is to be prepared.
This information is used by commands, such as
.I nroff
or
.IR plot (1),
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 the name of the termcap file, see
.IR termcap (3X), termcap (5).
.TP
EXINIT
A startup list of commands read by
.IR ex (1),
.IR edit (1),
and
.IR vi (1).
.TP
USER
The login name of the user.
.PP
Further names may be placed in the environment by the
.I export
command and `name=value' arguments in
.IR sh (1),
or by the
.I setenv
command if you use
.IR csh (1).
Arguments may also be placed in the environment at the point of an
.IR execve (2).
It is unwise to conflict with certain 
.IR sh (1)
variables that are frequently exported by `.profile' files:
MAIL, PS1, PS2, IFS.
.SH SEE ALSO
csh(1), ex(1), login(1), sh(1), execve(2), exec(3), system(3S),
termcap(3X), termcap(5)