[apple/libc.git] / stdlib / 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 1.12 2001/09/07 14:46:35 asmodai 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
.Ar name
and
.Ar 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,
.Ar name .
If the variable
.Ar name
is not in the current environment,
a null pointer is returned.
.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
.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
.Ar value
to the same
.Ar name
will result in a memory leak.  The
.Fx
semantics for these functions
(namely, that the contents of
.Ar 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
	37	.\" $FreeBSD: src/lib/libc/stdlib/getenv.3,v 1.12 2001/09/07 14:46:35 asmodai 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	.Ar name
67	and
68	.Ar 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	.Ar name .
78	If the variable
79	.Ar name
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
86	.Ar name
87	in the current environment list.
88	If the variable
89	.Ar name
90	does not exist in the list,
91	it is inserted with the given
92	.Ar value .
93	If the variable does exist, the argument
94	.Ar overwrite
95	is tested; if
96	.Ar overwrite is
97	zero, the
98	variable is not reset, otherwise it is reset
99	to the given
100	.Ar value .
101	.Pp
102	The
103	.Fn putenv
104	function takes an argument of the form ``name=value'' and is
105	equivalent to:
106	.Bd -literal -offset indent
107	setenv(name, value, 1);
108	.Ed
109	.Pp
110	The
111	.Fn unsetenv
112	function
113	deletes all instances of the variable name pointed to by
114	.Fa name
115	from the list.
116	.Sh RETURN VALUES
117	.Rv -std setenv putenv
118	.Sh ERRORS
119	.Bl -tag -width Er
120	.It Bq Er ENOMEM
121	The function
122	.Fn setenv
123	or
124	.Fn putenv
125	failed because they were unable to allocate memory for the environment.
126	.El
127	.Sh SEE ALSO
128	.Xr csh 1 ,
129	.Xr sh 1 ,
130	.Xr execve 2 ,
131	.Xr environ 7
132	.Sh STANDARDS
133	The
134	.Fn getenv
135	function conforms to
136	.St -isoC .
137	.Sh BUGS
138	Successive calls to
139	.Fn setenv
140	or
141	.Fn putenv
142	assigning a differently sized
143	.Ar value
144	to the same
145	.Ar name
146	will result in a memory leak. The
147	.Fx
148	semantics for these functions
149	(namely, that the contents of
150	.Ar value
151	are copied and that old values remain accessible indefinitely) make this
152	bug unavoidable. Future versions may eliminate one or both of these
153	semantic guarantees in order to fix the bug.
154	.Sh HISTORY
155	The functions
156	.Fn setenv
157	and
158	.Fn unsetenv
159	appeared in
160	.At v7 .
161	The
162	.Fn putenv
163	function appeared in
164	.Bx 4.3 Reno .