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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
PUTENV(3) Linux Programmer's Manual PUTENV(3)
putenv - change or add an environment variable
#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
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.
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.
ENOMEM Insufficient space to allocate new environment.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────┬───────────────┬─────────────────────┐
│Interface │ Attribute │ Value │
├──────────┼───────────────┼─────────────────────┤
│putenv() │ Thread safety │ MT-Unsafe const:env │
└──────────┴───────────────┴─────────────────────┘
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
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.
clearenv(3), getenv(3), setenv(3), unsetenv(3), environ(7)
This page is part of release 4.12 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/.
GNU 2016-03-15 PUTENV(3)
Pages that refer to this page: clearenv(3), getenv(3), pam_putenv(3), pmgetconfig(3), setenv(3), proc(5), environ(7)