@code{setenv} adds @var{name} to the environment with value
@var{value}. If the name was already present in the environment,
-the new value will be stored only if @var{overwrite} is non-zero.
+the new value will be stored only if @var{overwrite} is nonzero.
The companion @code{unsetenv} function removes @var{name} from the
environment. This implementation is not safe for multithreaded code.