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	1	.\" Copyright (c) 1988, 1991, 1993
	2	.\" The Regents of the University of California. All rights reserved.
	3	.\"
	4	.\" This code is derived from software contributed to Berkeley by
	5	.\" the American National Standards Committee X3, on Information
	6	.\" Processing Systems.
	7	.\"
	8	.\" Redistribution and use in source and binary forms, with or without
	9	.\" modification, are permitted provided that the following conditions
	10	.\" are met:
	11	.\" 1. Redistributions of source code must retain the above copyright
	12	.\" notice, this list of conditions and the following disclaimer.
	13	.\" 2. Redistributions in binary form must reproduce the above copyright
	14	.\" notice, this list of conditions and the following disclaimer in the
	15	.\" documentation and/or other materials provided with the distribution.
	16	.\" 3. All advertising materials mentioning features or use of this software
	17	.\" must display the following acknowledgement:
	18	.\" This product includes software developed by the University of
	19	.\" California, Berkeley and its contributors.
	20	.\" 4. Neither the name of the University nor the names of its contributors
	21	.\" may be used to endorse or promote products derived from this software
	22	.\" without specific prior written permission.
	23	.\"
	24	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	25	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	26	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	27	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	28	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	29	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	30	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	31	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	32	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	33	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	34	.\" SUCH DAMAGE.
	35	.\"
	36	.\" @(#)getenv.3 8.2 (Berkeley) 12/11/93
	37	.\" $FreeBSD: src/lib/libc/stdlib/getenv.3,v 1.16 2004/07/07 19:57:13 ru Exp $
	38	.\"
	39	.Dd December 11, 1993
	40	.Dt GETENV 3
	41	.Os
	42	.Sh NAME
	43	.Nm getenv ,
	44	.Nm putenv ,
	45	.Nm setenv ,
	46	.Nm unsetenv
	47	.Nd environment variable functions
	48	.Sh LIBRARY
	49	.Lb libc
	50	.Sh SYNOPSIS
	51	.In stdlib.h
	52	.Ft char *
	53	.Fn getenv "const char *name"
	54	.Ft int
	55	.Fn setenv "const char name" "const char value" "int overwrite"
	56	.Ft int
	57	.Fn putenv "const char *string"
	58	.Ft void
	59	.Fn unsetenv "const char *name"
	60	.Sh DESCRIPTION
	61	These functions set, unset and fetch environment variables from the
	62	host
	63	.Em environment list .
	64	For compatibility with differing environment conventions,
	65	the given arguments
	66	.Fa name
	67	and
	68	.Fa value
	69	may be appended and prepended,
	70	respectively,
	71	with an equal sign
	72	.Dq Li \&= .
	73	.Pp
	74	The
	75	.Fn getenv
	76	function obtains the current value of the environment variable,
	77	.Fa name .
	78	.Pp
	79	The
	80	.Fn setenv
	81	function inserts or resets the environment variable
	82	.Fa name
	83	in the current environment list.
	84	If the variable
	85	.Fa name
	86	does not exist in the list,
	87	it is inserted with the given
	88	.Fa value .
	89	If the variable does exist, the argument
	90	.Fa overwrite
	91	is tested; if
	92	.Fa overwrite
	93	is
	94	zero, the
	95	variable is not reset, otherwise it is reset
	96	to the given
	97	.Fa value .
	98	.Pp
	99	The
	100	.Fn putenv
	101	function takes an argument of the form ``name=value'' and is
	102	equivalent to:
	103	.Bd -literal -offset indent
	104	setenv(name, value, 1);
	105	.Ed
	106	.Pp
	107	The
	108	.Fn unsetenv
	109	function
	110	deletes all instances of the variable name pointed to by
	111	.Fa name
	112	from the list.
	113	.Sh RETURN VALUES
	114	The
	115	.Fn getenv
	116	function returns the value of the environment variable as a
	117	.Dv NUL Ns
	118	-terminated string.
	119	If the variable
	120	.Fa name
	121	is not in the current environment,
	122	.Dv NULL
	123	is returned.
	124	.Pp
	125	.Rv -std setenv putenv
	126	.Sh ERRORS
	127	.Bl -tag -width Er
	128	.It Bq Er ENOMEM
	129	The function
	130	.Fn setenv
	131	or
	132	.Fn putenv
	133	failed because they were unable to allocate memory for the environment.
	134	.El
	135	.Sh SEE ALSO
	136	.Xr csh 1 ,
	137	.Xr sh 1 ,
	138	.Xr execve 2 ,
	139	.Xr environ 7
	140	.Sh STANDARDS
	141	The
	142	.Fn getenv
	143	function conforms to
	144	.St -isoC .
	145	.Sh BUGS
	146	Successive calls to
	147	.Fn setenv
	148	or
	149	.Fn putenv
	150	assigning a differently sized
	151	.Fa value
	152	to the same
	153	.Fa name
	154	will result in a memory leak.
	155	The
	156	.Fx
	157	semantics for these functions
	158	(namely, that the contents of
	159	.Fa value
	160	are copied and that old values remain accessible indefinitely) make this
	161	bug unavoidable.
	162	Future versions may eliminate one or both of these
	163	semantic guarantees in order to fix the bug.
	164	.Sh HISTORY
	165	The functions
	166	.Fn setenv
	167	and
	168	.Fn unsetenv
	169	appeared in
	170	.At v7 .
	171	The
	172	.Fn putenv
	173	function appeared in
	174	.Bx 4.3 Reno .