PUTENV(3) Linux Programmer's Manual PUTENV(3)
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 vari-
ables. The argument string is of the form name=value. If name does
not already exist in the environment, then string is added to the envi-
ronment. 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 at-
tributes(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 en-
vironment. (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.
SEE ALSO
clearenv(3), getenv(3), setenv(3), unsetenv(3), environ(7)
COLOPHON
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GNU 2019-03-06 PUTENV(3)