setenv(3) — Linux manual page
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 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.1-2008.
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)
COLOPHON
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Linux man-pages 6.9.1 2024-05-02 setenv(3)
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