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 versions <= 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 variables 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 at-
tributes(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 <section>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 applica-
tions 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 vari-
ables.
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)
COLOPHON
This page is part of release 5.07 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2017-09-15 CLEARENV(3)