[apple/libc.git] / stdlib / FreeBSD / getenv.3

.\" 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. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. 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.
.\"
.\"     @(#)getenv.3	8.2 (Berkeley) 12/11/93
.\" $FreeBSD: src/lib/libc/stdlib/getenv.3,v 1.13 2002/12/18 13:33:03 ru Exp $
.\"
.Dd December 11, 1993
.Dt GETENV 3
.Os
.Sh NAME
.Nm getenv ,
.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 setenv "const char *name" "const char *value" "int overwrite"
.Ft int
.Fn putenv "const char *string"
.Ft void
.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
.Fa name
and
.Fa value
may be appended and prepended,
respectively,
with an equal sign
.Dq Li \&= .
.Pp
The
.Fn getenv
function obtains the current value of the environment variable,
.Fa name .
If the variable
.Fa name
is not in the current environment,
a null pointer is returned.
.Pp
The
.Fn setenv
function inserts or resets the environment variable
.Fa name
in the current environment list.
If the variable
.Fa name
does not exist in the list,
it is inserted with the given
.Fa value .
If the variable does exist, the argument
.Fa overwrite
is tested; if
.Fa overwrite
is
zero, the
variable is not reset, otherwise it is reset
to the given
.Fa 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
.Rv -std setenv putenv
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er ENOMEM
The function
.Fn setenv
or
.Fn putenv
failed because they were unable to allocate memory for the environment.
.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 -isoC .
.Sh BUGS
Successive calls to
.Fn setenv
or
.Fn putenv
assigning a differently sized
.Fa value
to the same
.Fa name
will result in a memory leak.  The
.Fx
semantics for these functions
(namely, that the contents of
.Fa value
are copied and that old values remain accessible indefinitely) make this
bug unavoidable.  Future versions may eliminate one or both of these
semantic guarantees in order to fix the bug.
.Sh HISTORY
The functions
.Fn setenv
and
.Fn unsetenv
appeared in
.At v7 .
The
.Fn putenv
function appeared in
.Bx 4.3 Reno .
Commit	Line	Data
5b2abdfb A	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
9385eb3d	37	.\" $FreeBSD: src/lib/libc/stdlib/getenv.3,v 1.13 2002/12/18 13:33:03 ru Exp $
5b2abdfb A	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
9385eb3d	66	.Fa name
5b2abdfb	67	and
9385eb3d	68	.Fa value
5b2abdfb A	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,
9385eb3d	77	.Fa name .
5b2abdfb	78	If the variable
9385eb3d	79	.Fa name
5b2abdfb A	80	is not in the current environment,
	81	a null pointer is returned.
	82	.Pp
	83	The
	84	.Fn setenv
	85	function inserts or resets the environment variable
9385eb3d	86	.Fa name
5b2abdfb A	87	in the current environment list.
5b2abdfb A	88	If the variable
9385eb3d	89	.Fa name
5b2abdfb A	90	does not exist in the list,
5b2abdfb A	91	it is inserted with the given
9385eb3d	92	.Fa value .
5b2abdfb	93	If the variable does exist, the argument
9385eb3d	94	.Fa overwrite
5b2abdfb	95	is tested; if
9385eb3d A	96	.Fa overwrite
9385eb3d A	97	is
5b2abdfb A	98	zero, the
	99	variable is not reset, otherwise it is reset
	100	to the given
9385eb3d	101	.Fa value .
5b2abdfb A	102	.Pp
	103	The
	104	.Fn putenv
	105	function takes an argument of the form ``name=value'' and is
	106	equivalent to:
	107	.Bd -literal -offset indent
	108	setenv(name, value, 1);
	109	.Ed
	110	.Pp
	111	The
	112	.Fn unsetenv
	113	function
	114	deletes all instances of the variable name pointed to by
	115	.Fa name
	116	from the list.
	117	.Sh RETURN VALUES
	118	.Rv -std setenv putenv
	119	.Sh ERRORS
	120	.Bl -tag -width Er
	121	.It Bq Er ENOMEM
	122	The function
	123	.Fn setenv
	124	or
	125	.Fn putenv
	126	failed because they were unable to allocate memory for the environment.
	127	.El
	128	.Sh SEE ALSO
	129	.Xr csh 1 ,
	130	.Xr sh 1 ,
	131	.Xr execve 2 ,
	132	.Xr environ 7
	133	.Sh STANDARDS
	134	The
	135	.Fn getenv
	136	function conforms to
	137	.St -isoC .
	138	.Sh BUGS
	139	Successive calls to
	140	.Fn setenv
	141	or
	142	.Fn putenv
	143	assigning a differently sized
9385eb3d	144	.Fa value
5b2abdfb	145	to the same
9385eb3d	146	.Fa name
5b2abdfb A	147	will result in a memory leak. The
	148	.Fx
	149	semantics for these functions
	150	(namely, that the contents of
9385eb3d	151	.Fa value
5b2abdfb A	152	are copied and that old values remain accessible indefinitely) make this
	153	bug unavoidable. Future versions may eliminate one or both of these
	154	semantic guarantees in order to fix the bug.
	155	.Sh HISTORY
	156	The functions
	157	.Fn setenv
	158	and
	159	.Fn unsetenv
	160	appeared in
	161	.At v7 .
	162	The
	163	.Fn putenv
	164	function appeared in
	165	.Bx 4.3 Reno .