1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
3 .\" %%%LICENSE_START(VERBATIM)
4 .\" Permission is granted to make and distribute verbatim copies of this
5 .\" manual provided the copyright notice and this permission notice are
6 .\" preserved on all copies.
8 .\" Permission is granted to copy and distribute modified versions of this
9 .\" manual under the conditions for verbatim copying, provided that the
10 .\" entire resulting derived work is distributed under the terms of a
11 .\" permission notice identical to this one.
13 .\" Since the Linux kernel and libraries are constantly changing, this
14 .\" manual page may be incorrect or out-of-date. The author(s) assume no
15 .\" responsibility for errors or omissions, or for damages resulting from
16 .\" the use of the information contained herein. The author(s) may not
17 .\" have taken the same level of care in the production of this manual,
18 .\" which is licensed free of charge, as they might when working
21 .\" Formatted or processed versions of this manual, if unaccompanied by
22 .\" the source, must acknowledge the copyright and authors of this work.
25 .\" References consulted:
26 .\" Linux libc source code
27 .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
29 .\" Single UNIX Specification, Version 2
30 .\" Modified Thu Apr 8 15:00:12 1993, David Metcalfe
31 .\" Modified Sat Jul 24 18:44:45 1993, Rik Faith (faith@cs.unc.edu)
32 .\" Modified Fri Feb 14 21:47:50 1997 by Andries Brouwer (aeb@cwi.nl)
33 .\" Modified Mon Oct 11 11:11:11 1999 by Andries Brouwer (aeb@cwi.nl)
34 .\" Modified Wed Nov 10 00:02:26 1999 by Andries Brouwer (aeb@cwi.nl)
35 .\" Modified Sun May 20 22:17:20 2001 by Andries Brouwer (aeb@cwi.nl)
36 .TH PUTENV 3 2019-03-06 "GNU" "Linux Programmer's Manual"
38 putenv \- change or add an environment variable
41 .B #include <stdlib.h>
43 .BI "int putenv(char *" string );
48 Feature Test Macro Requirements for glibc (see
49 .BR feature_test_macros (7)):
54 || /* Glibc since 2.19: */ _DEFAULT_SOURCE
55 || /* Glibc versions <= 2.19: */ _SVID_SOURCE
59 function adds or changes the value of environment
61 The argument \fIstring\fP is of the form \fIname\fP=\fIvalue\fP.
62 If \fIname\fP does not already exist in the environment, then
63 \fIstring\fP is added to the environment.
64 If \fIname\fP does exist,
65 then the value of \fIname\fP in the environment is changed to
67 The string pointed to by \fIstring\fP becomes part of the environment,
68 so altering the string changes the environment.
72 function returns zero on success,
73 or nonzero if an error occurs.
74 In the event of an error,
76 is set to indicate the cause.
80 Insufficient space to allocate new environment.
82 For an explanation of the terms used in this section, see
88 Interface Attribute Value
91 T} Thread safety MT-Unsafe const:env
94 POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
98 function is not required to be reentrant, and the
99 one in glibc 2.0 is not, but the glibc 2.1 version is.
101 .\" Description for libc4, libc5, glibc:
102 .\" If the argument \fIstring\fP is of the form \fIname\fP,
103 .\" and does not contain an \(aq=\(aq character, then the variable \fIname\fP
104 .\" is removed from the environment.
107 .\" has to allocate a new array \fIenviron\fP,
108 .\" and the previous array was also allocated by
110 .\" then it will be freed.
111 .\" In no case will the old storage associated
112 .\" to the environment variable itself be freed.
114 Since version 2.1.2, the glibc implementation conforms to SUSv2:
115 the pointer \fIstring\fP given to
118 In particular, this string becomes part of the environment;
119 changing it later will change the environment.
120 (Thus, it is an error to call
122 with an automatic variable
123 as the argument, then return from the calling function while \fIstring\fP
124 is still part of the environment.)
125 However, glibc versions 2.0 to 2.1.1 differ: a copy of the string is used.
126 On the one hand this causes a memory leak, and on the other hand
129 The 4.4BSD version, like glibc 2.0, uses a copy.
131 SUSv2 removes the \fIconst\fP from the prototype, and so does glibc 2.1.3.
133 The GNU C library implementation provides a nonstandard extension.
136 does not include an equal sign:
144 then the named variable is removed from the caller's environment.