為什麼鍵盤上有下劃線「_」這個符號？它的起源是什麼？

01-07

簡單回答，現在所用的計算機鍵盤，緣自打字機時代的拉丁字母鍵盤。

在打字機時代，下劃線的作用就是用於輸入需要手工填寫的那部分的橫線，

您知道填空題吧？對的，就是它。

在富文本時代，一般的編輯器都能生成下劃線，用不著用字元來表示，

但是在這之前，這一功能是沒有的，所以「下劃線」這個字元是必須的。

不單只有下劃線，那個時候連表格都是使用製表符來拼湊的。

所以計算機編碼保留了這些字元，相應的，在鍵盤上也保留了下劃線的鍵位。

以下轉自維基百科

The symbol underscore [ _ ] (also called underline, underbar,low line, or low dash) is a character that originally appeared on the typewriter and was primarily used to underline words. To produce an underlined word, the word was typed, the typewriter carriage was moved back to the beginning of the word, and the word was overtyped with the underscore character.

最早出現在打字機上，用來給輸入好的內容加下劃線。

This character is sometimes used to create visual spacing within a sequence of characters, where a whitespace characteris not permitted (e.g., in computer filenames, email addresses, and in Internet URLs). Some computer applications will automatically underline text surrounded by underscores: _underlined_ will render underlined. It is often used in plain text-only media (IRC, instant messaging, classical Email) for this purpose. When the underscore is used for emphasis in this fashion, it is usually interpreted as indicating that the enclosed text is underlined (as opposed to being italicized or bold, which is indicated by /slashes/ or *asterisks*, respectively).

後來的用途是當不讓輸入空格時，作為空格的替補，比如郵箱地址、網址之類的。

The underscore is not the same character as the dash character, although one convention for text news wires is to use an underscore when an em-dash or en-dash is desired, or when other non-standard characters such as bullets would be appropriate. A series of underscores [like ___-______ ] may be used to create a blank to be filled in on a form, although the resulting blank may have tiny gaps between each individual underscore. It is also sometimes used to create a horizontal line; other symbols with similar graphemes, such as hyphens and dashes, are also used for this purpose.

或者，其他用途，比如製作填空。

為了跟減號（-）區分

計算機程序中，bill_gates是一個變數明，而bill-gates是兩個變數相減。

個人感覺，是為了跟空格區分

在命令行操作系統中，空格是天然的欄位分隔符，但是，同一個欄位中有可能包含多個word，那麼就用一個跟空格類似的符號來表示吧

下劃線的起源不知道，但是一直伴隨著文本處理，很重要的感覺！

引用：http://wapbaike.baidu.com/view/547703.htm?ssid=0from=1099buid=C5AA1AAE9AAA821FAEAC39DEF43BD445pu=usm%401%2Csz%401320_2001%2Cta%40iphone_1_7.0_3_537bd_page_type=1baiduid=729C3B380EB38821A9C0ADAABB604789tj=Xk_2_0_10_title