Section (3) clearenv
clearenv — clear the environment
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).
For an explanation of the terms used in this section, see attributes(7).
||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 (see [sc]B.4.6.1). However, POSIX.1-2001 adds
only putenv(3), and rejected
On systems where
is unavailable, the assignment
environ = NULL;
will probably do.
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
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.
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and the latest version of this page, can be found at
Copyright 2001 John Levon <mozcompsoc.man.ac.uk>
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