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)