hash.c:1722
static int
env_update_i(key, val)
    VALUE key, val;
{
    if (key != Qundef) {
	if (rb_block_given_p()) {
	    val = rb_yield_values(3, key, rb_f_getenv(Qnil, key), val);
	}
	env_aset(Qnil, key, val);
    }
    return ST_CONTINUE;
}
