clearenv(3) - Linux manual page (original) (raw)
clearenv(3) Library Functions Manual clearenv(3)
NAME top
clearenv - clear the environmentLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <stdlib.h>**
**int clearenv(void);**Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
**clearenv**():
/* glibc >= 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCEDESCRIPTION top
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)](../man3/putenv.3.html) and [setenv(3)](../man3/setenv.3.html).RETURN VALUE top
The **clearenv**() function returns zero on success, and a nonzero
value on failure.ATTRIBUTES top
For an explanation of the terms used in this section, see
[attributes(7)](../man7/attributes.7.html).
┌──────────────────────────┬───────────────┬─────────────────────┐
│ **Interface** │ **Attribute** │ **Value** │
├──────────────────────────┼───────────────┼─────────────────────┤
│ **clearenv**() │ Thread safety │ MT-Unsafe const:env │
└──────────────────────────┴───────────────┴─────────────────────┘STANDARDS top
**putenv**()
POSIX.1-2008.
**clearenv**()
None.HISTORY top
**putenv**()
glibc 2.0. POSIX.1-2001.
**clearenv**()
glibc 2.0.
Various UNIX variants (DG/UX, HP-UX, QNX, ...). POSIX.9 (bindings
for FORTRAN77). POSIX.1-1996 did not accept **clearenv**() and
[putenv(3)](../man3/putenv.3.html), 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)](../man3/putenv.3.html), and rejected **clearenv**().NOTES top
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)](../man3/exec.3.html). 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)](../man7/environ.7.html); 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)](../man3/putenv.3.html), [getenv(3)](../man3/getenv.3.html), or **clearenv**()
functions, then **clearenv**() will return an error and the process
environment will remain unchanged.SEE ALSO top
[getenv(3)](../man3/getenv.3.html), [putenv(3)](../man3/putenv.3.html), [setenv(3)](../man3/setenv.3.html), [unsetenv(3)](../man3/unsetenv.3.html), [environ(7)](../man7/environ.7.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 clearenv(3)
Pages that refer to this page:getenv(3), putenv(3), setenv(3), environ(7)