clearenv - clear the environment

       For an explanation of the terms used in this section, see attributes(7).
       ┌─────────────────────────────────────────────────────────────────┬───────────────┬─────────────────────┐
       │ Interface                                                       │ Attribute     │ Value               │
       ├─────────────────────────────────────────────────────────────────┼───────────────┼─────────────────────┤
       │ clearenv()                                                      │ Thread safety │ MT-Unsafe const:env │
       └─────────────────────────────────────────────────────────────────┴───────────────┴─────────────────────┘

       The clearenv() function clears the environment of all name-value pairs and sets the value of the external
       variable environ to NULL.  After this call, new variables can be added to the environment using putenv(3)
       and setenv(3).

putenv()
              glibc 2.0.  POSIX.1-2001.

       clearenv()
              glibc 2.0.

       Various  UNIX variants (DG/UX, HP-UX, QNX, ...).  POSIX.9 (bindings for FORTRAN77).  POSIX.1-1996 did not
       accept clearenv() and putenv(3), but changed its mind and scheduled these functions for some later  issue
       of this standard (see §B.4.6.1).  However, POSIX.1-2001 adds only putenv(3), and rejected clearenv().

       Standard C library (libc, -lc)

       clearenv - clear the environment

       On systems where clearenv() is unavailable, the assignment

           environ = NULL;

       will probably do.

       The  clearenv()  function may be useful in security-conscious applications that want to precisely control
       the environment that is passed to programs executed using exec(3).  The  application  would  do  this  by
       first clearing the environment and then adding select environment variables.

       Note  that  the main effect of clearenv() is to adjust the value of the pointer environ(7); this function
       does not erase the contents of the buffers containing the environment definitions.

       The DG/UX and Tru64 man pages write: If environ has been modified by anything other than  the  putenv(3),
       getenv(3), or clearenv() functions, then clearenv() will return an error and the process environment will
       remain unchanged.

       The clearenv() function returns zero on success, and a nonzero value on failure.

getenv(3), putenv(3), setenv(3), unsetenv(3), environ(7)

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

putenv()
              POSIX.1-2008.

       clearenv()
              None.

#include<stdlib.h>intclearenv(void);

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

       clearenv():
           /* glibc >= 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE