The writ is either alternative or peremptory. The alternative writ must state, concisely, the fact showing the obligation of the defendant to perform the act, and his omission to perform it, and command him that immediately upon the receipt of the writ, or at some other specified time, he do the act required to be performed or show cause before the court whence the writ issued, at a specified time and place, why he has not done so; and that he then and there return the writ with his certificate of having done as he is commanded. The peremptory writ must be in a similar form, except that the words requiring the defendant to show cause why he has not done as commanded, must be omitted.