UNSETENV(P) POSIX Programmer's Manual UNSETENV(P)
unsetenv - remove an environment variable
int unsetenv(const char *name);
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 vari-
able 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 reen-
trant is not required to be thread-safe.
Upon successful completion, zero shall be returned. Otherwise, -1 shall be returned, errno
set to indicate the error, and the environment shall be unchanged.
The unsetenv() function shall fail if:
EINVAL The name argument is a null pointer, points to an empty string, or points to a
string containing an '=' character.
The following sections are informative.
Refer to the RATIONALE section in setenv() .
getenv() , setenv() , the Base Definitions volume of IEEE Std 1003.1-2001, <stdlib.h>,
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 UNSETENV(P)