setenv - change or add an environment variable
#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 versions <= 2.19: */ _BSD_SOURCE
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.
The
setenv() function returns zero on success, or -1 on error, with
errno set to indicate the cause of the error.
The
unsetenv() function returns zero on success, or -1 on error, with
errno set to indicate the cause of the error.
- 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.
For an explanation of the terms used in this section, see
attributes(7).
| Interface |
Attribute |
Value |
| setenv (), unsetenv () |
Thread safety |
MT-Unsafe const:env |
POSIX.1-2001, POSIX.1-2008, 4.3BSD.
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.
POSIX.1 specifies that if
name contains an '=' character, then
setenv() should fail with the error
EINVAL; however, versions of
glibc before 2.3.4 allowed an '=' sign in
name.
clearenv(3),
getenv(3),
putenv(3),
environ(7)