ENV.clone

static VALUE
env_clone(int argc, VALUE *argv, VALUE obj)
{
    if (argc) {
        VALUE opt;
        if (rb_scan_args(argc, argv, "0:", &opt) < argc) {
            rb_get_freeze_opt(1, &opt);
        }
    }

    rb_raise(rb_eTypeError, "Cannot clone ENV, use ENV.to_h to get a copy of ENV as a hash");
}