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.
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 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.
The GNU C library implementation provides a nonstandard extension. If
string
does not include an equal sign:
putenv("NAME");
then the named variable is removed from the caller's environment.
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