setenv - change or add an environment variable

       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  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.

       POSIX.1 does not require setenv() or unsetenv() to be reentrant.

       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.

EINVALname is NULL, points to a string of length 0, or contains an '=' character.

       ENOMEM Insufficient memory to add a new variable to the environment.

       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.

       Standard C library (libc, -lc)

       setenv - change or add an environment variable

setenv()  and unsetenv() functions return zero on success, or -1 on error, with errno set to indicate the
       error.

clearenv(3), getenv(3), putenv(3), environ(7)

Linux man-pages 6.9.1                              2024-05-02                                          setenv(3)

       POSIX.1-2008.

#include<stdlib.h>intsetenv(constchar*name,constchar*value,intoverwrite);intunsetenv(constchar*name);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       setenv(), unsetenv():
           _POSIX_C_SOURCE >= 200112L
               || /* glibc <= 2.19: */ _BSD_SOURCE