V8/usr/man/man5/environ.5

.TH ENVIRON 5
.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 exec (2)
when a process begins.
By convention these strings have either the form
.RI ` name = value ',
defining a variable, or
.RI ` name ()\|{ value }\|',
defining a function (see
.IR sh (1)).
The following variables 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/bin.
.TP
HOME
A user's login directory, set by
.IR login (8)
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
for a list of terminal types.
.TP
SHELL
The name of the login shell.
.PP
The environment may be queried by
.IR getenv (3)
or by the
.I set
or
.I whatis
commands of 
.IR sh (1).
Names may be placed in the environment by
the
.I export
command by and `name=value' arguments in
.IR sh (1).
Names may also be placed in the environment at the point of an
.IR exec (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
sh(1), exec(2), getenv(3), term(7)