putenv
Section: C Library Functions (3)
Updated: 2023-02-05
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NAME
putenv - change or add an environment variable
LIBRARY
Standard C library
(libc, -lc)
SYNOPSIS
#include <stdlib.h>
int putenv(char *string);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
putenv():
_XOPEN_SOURCE
|| /* glibc >= 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 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.
On failure, it returns a nonzero value, and
errno
is set to indicate the error.
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
|
STANDARDS
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 glibc 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, from glibc 2.0 to glibc 2.1.1, it differs:r
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)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- ATTRIBUTES
-
- STANDARDS
-
- NOTES
-
- SEE ALSO
-
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