setenv(3) Library Functions Manual setenv(3)
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 er-
ror, 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.1-2008.
HISTORY
POSIX.1-2001, 4.3BSD.
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.
CAVEATS
POSIX.1 does not require setenv() or unsetenv() to be reentrant.
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)
Linux man-pages 6.9.1 2024-05-02 setenv(3)
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