The unsetenv() function shall remove an environment variable from the
environment of the calling process. The name argument points to a
string, which is the name of the variable to be removed. The named argument
shall not contain an '=' character. If the named variable does not
exist in the current environment, the environment shall be unchanged and the
function is considered to have completed successfully.
If the application modifies environ or the pointers to which it points,
the behavior of unsetenv() is undefined. The unsetenv() function
shall update the list of pointers to which environ points.
The unsetenv() function need not be reentrant. A function that is not
required to be reentrant is not required to be thread-safe.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html