Section: Linux Programmer's Manual (3)
clearenv - clear the environment
Feature Test Macro Requirements for glibc (see
/* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
function clears the environment of all name-value
pairs and sets the value of the external variable
After this call, new variables can be added to the environment using
function returns zero on success, and a nonzero
value on failure.
Available since glibc 2.0.
For an explanation of the terms used in this section, see
||Thread safety||MT-Unsafe const:env|
Various UNIX variants (DG/UX, HP-UX, QNX, ...).
POSIX.9 (bindings for FORTRAN77).
POSIX.1-1996 did not accept
but changed its mind and scheduled these functions for some
later issue of this standard (see §B.4.6.1).
On systems where
is unavailable, the assignment
environ = NULL;
will probably do.
function may be useful in security-conscious applications that want to
precisely control the environment that is passed to programs
The application would do this by first clearing the environment
and then adding select environment variables.
Note that the main effect of
is to adjust the value of the pointer
this function does not erase the contents of the buffers
containing the environment definitions.
The DG/UX and Tru64 man pages write: If
has been modified by anything other than the
will return an error and the process environment will remain unchanged.
This page is part of release 5.07 of the Linux
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at