If you really want to match an equavalent English translation to “师傅 shīfu “, “Sir” is all right, they are still not the same in a formal way in terms of their social context. However, “Sir 先生 (xiansheng) /Madam 女士(nvshi) /Miss 小姐 (xiaojie)” is a borrowed term from English and French to formally and politely address a person who is somewhat from upper class. We often call a stranger at a meeting or other public gatherings “Sir 先生(xiansheng) /Madam女士(nvshi) /Miss 小姐(xiaojie)” to start a conversation, just because you know eaxactly they are not workers.
For the staff in a restaurant, we call a waiter or waitress “服务员” (wufu yuan), which means a staff to serve (fuwu). At a hotel, we also call a roomkeeper “服务员” (wufu yuan) . Alternatively, you may call the female staff “小姐” (xiaojie, Miss) all the time for a polite manner. But we still call the taxi-drivers, doormen and the bellmen 师傅 (shifu) most of the time.
Examples for comparion:
— (To a taxi driver) 师傅, 请送我去机场.
Shifu, qing song wo chu jichang.
Sir, please drive me to the airport.
— (At a banquet to ask a person sitting beside)
先生, 请问您在哪个部门工作?
Xiansheng, qingwen nin zai nage bumen gongzuo?
Sir, which department do you work, please?
— (At a hotel) 服务员, 帮我开一下门。 我忘记带钥匙了。
Fuwu yuan, bang wo kai yixia men. Wo wangji dai yaoshi le.
Miss, open the door for me please. I left the key in the room.
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Also, 师傅 shīfu can be used as 师父 shīfu (师shī – teacher, 父 fu – like a father) for a common address to a monk or nun, and a martial arts instructor. In the classic novel “Xi You Ji” (西游记,Journey to the West), you may find that Money King always called the monk Tang-Seng “师父 shīfu”. Chinese people traditionally respect their teachers as equally as their own parents, that is the reason why 师 shī is for a teacher, and 父 fu is like a father. Both “师傅” and “师父” are read “shifu”. Although in modern Chinese, lots of people mix them, they are still not the same in a formal way in terms of their social context.
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More examples:
1.—(In a shop) Shīfu, zhèige lǐngdài duōshao qián?
师傅,这个领带多少钱?Excuse me, sir. How much is this tie?
2.— (On a strreet) Shīfù, qǐngwèn fùjìn yǒu yínháng ma ?
师傅,请问附近有银行吗 ? Sir, is there a bank nearby ?
— Qiánmian jiùshì Zhōngguó Yínháng.
前面就是中国银行。To the front is Bank of China.
3. — (At a repair shop) Shīfù, wǒde shǒubiǎo huài le. Kěyǐ xiū ma ?
师傅,我的手表坏了。可以修吗?Sir, my watch doesn’t work. Can you have it fixed ?
— Ràng wǒ kànkan.
让我看看。Let me have a look.