setenv
Section: C Library Functions (3)
Updated: 2023-02-05
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NAME
setenv - change or add an environment variable
LIBRARY
Standard C library
(libc, -lc)
SYNOPSIS
#include <stdlib.h>
int setenv(const char *name, const char *value, int overwrite);
int unsetenv(const char *name);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
setenv(),
unsetenv():
_POSIX_C_SOURCE >= 200112L
|| /* glibc <= 2.19: */ _BSD_SOURCE
DESCRIPTION
The
setenv()
function adds the variable
name
to the
environment with the value
value,
if
name
does not
already exist.
If
name
does exist in the environment, then
its value is changed to
value
if
overwrite
is nonzero;
if
overwrite
is zero, then the value of
name
is not changed (and
setenv()
returns a success status).
This function makes copies of the strings pointed to by
name
and
value
(by contrast with
putenv(3)).
The
unsetenv()
function deletes the variable
name
from
the environment.
If
name
does not exist in the environment,
then the function succeeds, and the environment is unchanged.
RETURN VALUE
setenv()
and
unsetenv()
functions return zero on success,
or -1 on error, with
errno
set to indicate the error.
ERRORS
- EINVAL
-
name
is NULL, points to a string of length 0,
or contains an '=' character.
- ENOMEM
-
Insufficient memory to add a new variable to the environment.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
setenv(),
unsetenv()
| Thread safety | MT-Unsafe const:env
|
STANDARDS
POSIX.1-2001, POSIX.1-2008, 4.3BSD.
NOTES
POSIX.1 does not require
setenv()
or
unsetenv()
to be reentrant.
Prior to glibc 2.2.2,
unsetenv()
was prototyped
as returning
void;
more recent glibc versions follow the
POSIX.1-compliant prototype shown in the SYNOPSIS.
BUGS
POSIX.1 specifies that if
name
contains an '=' character, then
setenv()
should fail with the error
EINVAL;
however, versions of glibc before glibc 2.3.4 allowed an '=' sign in
name.
SEE ALSO
clearenv(3),
getenv(3),
putenv(3),
environ(7)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- ATTRIBUTES
-
- STANDARDS
-
- NOTES
-
- BUGS
-
- SEE ALSO
-
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