請問『You'll have to take a bus 』

你所舉的例子都是正確，只是各有不同的意思。

You will have to take a bus. 你會搭巴士。
You shall have to take a bus. 你需要搭巴士 （我想你搭巴士）。

You shall have it back next week. 下星期一定還你。 （我答應下星期還你）
He shall stay in bed. 他必須躺在床上。

本來第一身，I， we， 才要用 shall，但現代英語連第一身都改用 will.
Shall 很多時會在古老文章出現，且多和 THOU（古老的 YOU）， YOU， 一起用，聖經常見，是命令式， 如 THOU SHALT NOT KILL。現代英文這個 SHALL 則是用 SHOULD。 另一用法是承諾， PROMISE，如還錢給你 You shall your money back .

the traditional rules. The traditional rules state that you use shall to show what happens in the future only when I or we is the subject: I shall (not will) call you tomorrow. We shall (not will) be sure to keep in touch. Will, on the other hand, is used with subjects in the second and third persons: The comet will (not shall) return in 87 years. You will (not shall) probably encounter some heavy seas when you round the point. However, you can use will with a subject in the first person and shall with a subject in the second or third person to express determination, promise, obligation, or permission, depending on the context. Thus I will leave tomorrow indicates that the speaker is determined to leave. You shall leave tomorrow has the ring of a command. The sentence You shall have your money expresses a promise (“I will see that you get your money”), whereas You will have your money makes a simple prediction.

講是一套，做又是一套。現實生活中則是英美不同，怕只有英國人及重文法的人才用 SHALL，美國人怕用 SHALL， 怕被人說扮野，多數用 WILL。所以，你有天讀完書畢業後，可以只用 WILL，到時你見人用得 WILL 多便明。

這個課題我曾在外國的論壇解釋過，有不少 NATIVE SPEAKERS 也十分贊同。

the reality. The English and some sticklers about usage are probably the only people who follow these rules, and then not with perfect consistency. In America, people who try to adhere to them run the risk of sounding pretentious or haughty. Americans normally use will to express most of the senses reserved for shall in British usage. Americans use shall chiefly in first person invitations and questions that request an opinion or agreement, such as Shall we go?, and in certain fixed expressions, such as We shall overcome. In formal style, Americans use shall to express an explicit obligation, such as Applicants shall provide a proof of residence, though must or should works just as well here. In speech you can get the distinctions in meaning delineated in the traditional rules by putting stress on the auxiliary verb, as in I will leave tomorrow (“I intend to leave”). You can also choose another auxiliary verb, such as must or have to, that is less open to misinterpretation, or you can make your meaning clear by adding an adverb such as certainly.

http://www.bartleby.com/64/C001/056.html

1/ You will have to take a bus
2/ You shall have to take a bus
Both are correct! But....
1/ will .....is a more definite future tense 較肯定的語詞 (你需乘搭該巴士)
2/ shall ...is indefinite ...(你可以乘搭該巴士)

I agree that both of them are correct although people don't ususlly use shall with he, she, you, they, and it. However, it is not wrong to do that. We can also use shall to make suggestions, e.g. Shall we go?, and to imply rules, e.g. You shouldn't talk to your neighbours during lessons.

both sentences are correct. It is just that people seldom use the second sentence.

and may i say, all
I, we, they, he, she, it
can use shall.

2006-10-16 09:32:48 補充：
I am sorry, I would have to disagree with the point that [YOU] and [SHALL] will never be used together.I know people don't usually would not say it this way, but nonetheless, below is an example using both:You shall be free tomorrow night? Am I right?

Both sentences are correct.

The first one is correct.
Both (I) and (we) can use (shall), but (you), (they), (he), (she) and (it) can use (will) only.