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CLEARENV(3)                                                             Linux Programmer's Manual                                                            CLEARENV(3)

NAME
       clearenv - clear the environment

SYNOPSIS
       #include <stdlib.h>

       int clearenv(void);

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

       clearenv():
           /* Glibc since 2.19: */ _DEFAULT_SOURCE
               || /* Glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE

DESCRIPTION
       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 vari‐
       ables can be added to the environment using putenv(3) and setenv(3).

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

VERSIONS
       Available since glibc 2.0.

ATTRIBUTES
       For an explanation of the terms used in this section, see attributes(7).

       ┌──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────────────────┐
       │Interface                                                                                                                 │ Attribute     │ Value               │
       ├──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────────────────┤
       │clearenv()                                                                                                                │ Thread safety │ MT-Unsafe const:env │
       └──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────────────────┘

CONFORMING TO
       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().

NOTES
       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.

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

Linux                                                                          2021-03-22                                                                    CLEARENV(3)