PUTENV
Section: Linux Programmer's Manual (3)
Updated: 2016-03-15
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NAME
putenv - change or add an environment variable
SYNOPSIS
#include <stdlib.h>
int putenv(char *string);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
putenv():
_XOPEN_SOURCE
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _SVID_SOURCE
DESCRIPTION
The
putenv()
function adds or changes the value of environment
variables.
The argument
string is of the form
name=
value.
If
name does not already exist in the environment, then
string is added to the environment.
If
name does exist,
then the value of
name in the environment is changed to
value.
The string pointed to by
string becomes part of the environment,
so altering the string changes the environment.
RETURN VALUE
The
putenv()
function returns zero on success,
or nonzero if an error occurs.
In the event of an error,
errno
is set to indicate the cause.
ERRORS
- ENOMEM
-
Insufficient space to allocate new environment.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
putenv()
| Thread safety | MT-Unsafe const:env
|
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
NOTES
The
putenv()
function is not required to be reentrant, and the
one in glibc 2.0 is not, but the glibc 2.1 version is.
Since version 2.1.2, the glibc implementation conforms to SUSv2:
the pointer string given to
putenv()
is used.
In particular, this string becomes part of the environment;
changing it later will change the environment.
(Thus, it is an error is to call
putenv()
with an automatic variable
as the argument, then return from the calling function while string
is still part of the environment.)
However, glibc versions 2.0 to 2.1.1 differ: a copy of the string is used.
On the one hand this causes a memory leak, and on the other hand
it violates SUSv2.
The 4.4BSD version, like glibc 2.0, uses a copy.
SUSv2 removes the const from the prototype, and so does glibc 2.1.3.
SEE ALSO
clearenv(3),
getenv(3),
setenv(3),
unsetenv(3),
environ(7)
COLOPHON
This page is part of release 4.13 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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