CLEARENV
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
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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
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 (cf. 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)
COLOPHON
This page is part of release 4.13 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- VERSIONS
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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