.\"	$NetBSD: getenv.3,v 1.19 2005/09/26 10:56:54 wiz Exp $
.\"
.\" Copyright (c) 1988, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the American National Standards Committee X3, on Information
.\" Processing Systems.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     from: @(#)getenv.3	8.2 (Berkeley) 12/11/93
.\"
.Dd September 25, 2005
.Dt GETENV 3
.Os
.Sh NAME
.Nm getenv ,
.Nm getenv_r ,
.Nm putenv ,
.Nm setenv ,
.Nm unsetenv
.Nd environment variable functions
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft char *
.Fn getenv "const char *name"
.Ft int
.Fn getenv_r "const char *name" "char *buf" "size_t len"
.Ft int
.Fn setenv "const char *name" "const char *value" "int overwrite"
.Ft int
.Fn putenv "const char *string"
.Ft int
.Fn unsetenv "const char *name"
.Sh DESCRIPTION
These functions set, unset and fetch environment variables from the
host
.Em environment list .
For compatibility with differing environment conventions,
the given arguments
.Ar name
and
.Ar value
may be appended and prepended,
respectively,
with an equal sign
.Dq Li \&= ,
except for
.Fn unsetenv .
.Pp
The
.Fn getenv
function obtains the current value of the environment variable
.Ar name .
If the variable
.Ar name
is not in the current environment, a
.Dv NULL
pointer is returned.
.Pp
The
.Fn getenv_r
function obtains the current value of the environment variable
.Fa name
and copies it to
.Fa buf .
If
.Fa name
is not in the current environment, or the string length of the value of
.Fa name
is longer than
.Fa len
characters, then \-1 is returned and
.Va errno
is set to indicate the error.
.Pp
The
.Fn setenv
function inserts or resets the environment variable
.Ar name
in the current environment list.
If the variable
.Ar name
does not exist in the list,
it is inserted with the given
.Ar value .
If the variable does exist, the argument
.Ar overwrite
is tested; if
.Ar overwrite is
zero, the
variable is not reset, otherwise it is reset
to the given
.Ar value .
.Pp
The
.Fn putenv
function takes an argument of the form ``name=value'' and is
equivalent to:
.Bd -literal -offset indent
setenv(name, value, 1);
.Ed
.Pp
The
.Fn unsetenv
function
deletes all instances of the variable name pointed to by
.Fa name
from the list.
.Sh RETURN VALUES
The functions
.Fn getenv_r ,
.Fn setenv ,
.Fn putenv ,
and
.Fn unsetenv
return zero if successful; otherwise the global variable
.Va errno
is set to indicate the error and a
\-1 is returned.
.Pp
If
.Fn getenv
is successful, the string returned should be considered read-only.
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa name
argument to
.Fn unsetenv
is a null pointer, points to an empty string, or points to a string
containing an
.Dq Li \&=
character.
.It Bq Er ENOMEM
The function
.Fn setenv
or
.Fn putenv
failed because they were unable to allocate memory for the environment.
.El
The function
.Fn getenv_r
can return the following errors:
.Bl -tag -width Er
.It Bq Er ENOENT
The variable
.Fa name
was not found in the environment.
.It Bq Er ERANGE
The value of the named variable is too long to fit in the supplied buffer.
.El
.Sh SEE ALSO
.Xr csh 1 ,
.Xr sh 1 ,
.Xr execve 2 ,
.Xr environ 7
.Sh STANDARDS
The
.Fn getenv
function conforms to
.St -ansiC .
The
.Fn putenv
function conforms to
.St -xpg4 .
The
.Fn unsetenv
function conforms to
.St -p1003.1-2001 .
.Sh HISTORY
The functions
.Fn setenv
and
.Fn unsetenv
appeared in
.At v7 .
The
.Fn putenv
function appeared in
.Bx 4.3 Reno .