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[dragonfly.git] / lib / libc / stdlib / getenv.3
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1.\" Copyright (c) 1988, 1991, 1993
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36.\" @(#)getenv.3 8.2 (Berkeley) 12/11/93
37.\" $FreeBSD: src/lib/libc/stdlib/getenv.3,v 1.4.2.7 2001/12/14 18:33:58 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
61These functions set, unset and fetch environment variables from the
62host
63.Em environment list .
64For compatibility with differing environment conventions,
65the given arguments
66.Ar name
67and
68.Ar value
69may be appended and prepended,
70respectively,
71with an equal sign
72.Dq Li \&= .
73.Pp
74The
75.Fn getenv
76function obtains the current value of the environment variable,
77.Ar name .
78If the variable
79.Ar name
80is not in the current environment,
81a null pointer is returned.
82.Pp
83The
84.Fn setenv
85function inserts or resets the environment variable
86.Ar name
87in the current environment list.
88If the variable
89.Ar name
90does not exist in the list,
91it is inserted with the given
92.Ar value .
93If the variable does exist, the argument
94.Ar overwrite
95is tested; if
96.Ar overwrite is
97zero, the
98variable is not reset, otherwise it is reset
99to the given
100.Ar value .
101.Pp
102The
103.Fn putenv
104function takes an argument of the form ``name=value'' and is
105equivalent to:
106.Bd -literal -offset indent
107setenv(name, value, 1);
108.Ed
109.Pp
110The
111.Fn unsetenv
112function
113deletes all instances of the variable name pointed to by
114.Fa name
115from the list.
116.Sh RETURN VALUES
117.Rv -std setenv putenv
118.Sh ERRORS
119.Bl -tag -width Er
120.It Bq Er ENOMEM
121The function
122.Fn setenv
123or
124.Fn putenv
125failed 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
133The
134.Fn getenv
135function conforms to
136.St -isoC .
137.Sh BUGS
138Successive calls to
139.Fn setenv
140or
141.Fn putenv
142assigning a differently sized
143.Ar value
144to the same
145.Ar name
146will result in a memory leak. The
147.Fx
148semantics for these functions
149(namely, that the contents of
150.Ar value
151are copied and that old values remain accessible indefinitely) make this
152bug unavoidable. Future versions may eliminate one or both of these
153semantic guarantees in order to fix the bug.
154.Sh HISTORY
155The functions
156.Fn setenv
157and
158.Fn unsetenv
159appeared in
160.At v7 .
161The
162.Fn putenv
163function appeared in
164.Bx 4.3 Reno .