|
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
CLEARENV(3) Linux Programmer's Manual CLEARENV(3)
clearenv - clear the environment
#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
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).
The clearenv() 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
attributes(7).
┌───────────┬───────────────┬─────────────────────┐
│Interface │ Attribute │ Value │
├───────────┼───────────────┼─────────────────────┤
│clearenv() │ 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 clearenv() and
putenv(3), but changed its mind and scheduled these functions for
some later issue of this standard (cf. B.4.6.1). However,
POSIX.1-2001 adds only putenv(3), and rejected clearenv().
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.
getenv(3), putenv(3), setenv(3), unsetenv(3), environ(7)
This page is part of release 4.12 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 2016-03-15 CLEARENV(3)
Pages that refer to this page: getenv(3), putenv(3), setenv(3), environ(7)