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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. Neither the name of the University nor the names of its contributors
17.\" may be used to endorse or promote products derived from this software
18.\" without specific prior written permission.
19.\"
20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30.\" SUCH DAMAGE.
31.\"
32.\" $OpenBSD: getenv.3,v 1.8 2003/06/02 20:18:37 millert Exp $
33.\"
34.Dd December 11, 1993
35.Dt GETENV 3
36.Os
37.Sh NAME
38.Nm getenv ,
39.Nm putenv ,
40.Nm setenv ,
41.Nm unsetenv
42.Nd environment variable functions
43.Sh SYNOPSIS
44.Fd #include <stdlib.h>
45.Ft char *
46.Fn getenv "const char *name"
47.Ft int
48.Fn setenv "const char *name" "const char *value" "int overwrite"
49.Ft int
50.Fn putenv "const char *string"
51.Ft void
52.Fn unsetenv "const char *name"
53.Sh DESCRIPTION
54These functions set, unset, and fetch environment variables from the host
55.Em environment list .
56For compatibility with differing environment conventions, the given arguments
57.Fa name
58and
59.Fa value
60may be appended and prepended, respectively, with an equal sign
61.Dq Li \&= .
62.Pp
63The
64.Fn getenv
65function obtains the current value of the environment variable,
66.Fa name .
67If the variable
68.Fa name
69is not in the current environment, a null pointer is returned.
70.Pp
71The
72.Fn setenv
73function inserts or resets the environment variable
74.Fa name
75in the current environment list.
76If the variable
77.Fa name
78does not exist in the list, it is inserted with the given
79.Fa value .
80If the variable does exist, the argument
81.Fa overwrite
82is tested; if
83.Fa overwrite
84is zero, the variable is not reset, otherwise it is reset to the given
85.Fa value .
86.Pp
87The
88.Fn putenv
89function takes an argument of the form
90.Ar name Ns No = Ns Ar value
91and is equivalent to:
92.Bd -literal -offset indent
93setenv(name, value, 1);
94.Ed
95.Pp
96The
97.Fn unsetenv
98function deletes all instances of the variable name pointed to by
99.Fa name
100from the list.
101.Sh RETURN VALUES
102The functions
103.Fn setenv
104and
105.Fn putenv
106return zero if successful; otherwise the global variable
107.Va errno
108is set to indicate the error and \-1 is returned.
109.Pp
110If
111.Fn getenv
112is successful, the string returned should be considered read-only.
113.Sh ERRORS
114.Bl -tag -width [ENOMEM]
115.It Bq Er ENOMEM
116The function
117.Fn setenv
118or
119.Fn putenv
120failed because they were unable to allocate memory for the environment.
121.El
122.Sh SEE ALSO
123.Xr csh 1 ,
124.Xr sh 1 ,
125.Xr execve 2 ,
126.Xr environ 7
127.Sh STANDARDS
128The
129.Fn getenv
130function conforms to
131.St -ansiC .
132.Sh HISTORY
133The functions
134.Fn setenv
135and
136.Fn unsetenv
137appeared in
138.At v7 .
139The
140.Fn putenv
141function appeared in
142.Bx 4.3 Reno .