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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.\" $OpenBSD: getenv.3,v 1.7 2000/04/20 13:50:02 aaron Exp $
37.\"
38.Dd December 11, 1993
39.Dt GETENV 3
40.Os
41.Sh NAME
42.Nm getenv ,
43.Nm putenv ,
44.Nm setenv ,
45.Nm unsetenv
46.Nd environment variable functions
47.Sh SYNOPSIS
48.Fd #include <stdlib.h>
49.Ft char *
50.Fn getenv "const char *name"
51.Ft int
52.Fn setenv "const char *name" "const char *value" "int overwrite"
53.Ft int
54.Fn putenv "const char *string"
55.Ft void
56.Fn unsetenv "const char *name"
57.Sh DESCRIPTION
58These functions set, unset, and fetch environment variables from the host
59.Em environment list .
60For compatibility with differing environment conventions, the given arguments
61.Fa name
62and
63.Fa value
64may be appended and prepended, respectively, with an equal sign
65.Dq Li \&= .
66.Pp
67The
68.Fn getenv
69function obtains the current value of the environment variable,
70.Fa name .
71If the variable
72.Fa name
73is not in the current environment, a null pointer is returned.
74.Pp
75The
76.Fn setenv
77function inserts or resets the environment variable
78.Fa name
79in the current environment list.
80If the variable
81.Fa name
82does not exist in the list, it is inserted with the given
83.Fa value .
84If the variable does exist, the argument
85.Fa overwrite
86is tested; if
87.Fa overwrite
88is zero, the variable is not reset, otherwise it is reset to the given
89.Fa value .
90.Pp
91The
92.Fn putenv
93function takes an argument of the form
94.Ar name Ns No = Ns Ar value
95and is equivalent to:
96.Bd -literal -offset indent
97setenv(name, value, 1);
98.Ed
99.Pp
100The
101.Fn unsetenv
102function deletes all instances of the variable name pointed to by
103.Fa name
104from the list.
105.Sh RETURN VALUES
106The functions
107.Fn setenv
108and
109.Fn putenv
110return zero if successful; otherwise the global variable
111.Va errno
112is set to indicate the error and \-1 is returned.
113.Pp
114If
115.Fn getenv
116is successful, the string returned should be considered read-only.
117.Sh ERRORS
118.Bl -tag -width [ENOMEM]
119.It Bq Er ENOMEM
120The function
121.Fn setenv
122or
123.Fn putenv
124failed because they were unable to allocate memory for the environment.
125.El
126.Sh SEE ALSO
127.Xr csh 1 ,
128.Xr sh 1 ,
129.Xr execve 2 ,
130.Xr environ 7
131.Sh STANDARDS
132The
133.Fn getenv
134function conforms to
135.St -ansiC .
136.Sh HISTORY
137The functions
138.Fn setenv
139and
140.Fn unsetenv
141appeared in
142.At v7 .
143The
144.Fn putenv
145function appeared in
146.Bx 4.3 Reno .