hash.c:1445
static VALUE
env_clear()
{
    volatile VALUE keys;
    long i;
    
    rb_secure(4);
    keys = env_keys();

    for (i=0; i<RARRAY(keys)->len; i++) {
	VALUE val = rb_f_getenv(Qnil, RARRAY(keys)->ptr[i]);
	if (!NIL_P(val)) {
	    env_delete(Qnil, RARRAY(keys)->ptr[i]);
	}
    }
    return envtbl;
}
