When we speak of the command line, we are really referring to the shell. The shell is a program that takes keyboard commands and passes them to the operating system to carry out. Almost all Linux distributions supply a shell program from the GNU Project called bash. The name “bash” is an acronym for “Bourne Again SHell”, a reference to the fact bash is an enhanced replacement for sh, the original Unix shell program written by Steve Bourne.
一說到命令列，我們真正指的是 shell。shell 就是一個程式，它接受從鍵盤輸入的命令， 然後把命令傳遞給作業系統去執行。幾乎所有的 Linux 發行版都提供一個名為 bash 的 來自 GNU 專案的 shell 程式。“bash” 是 “Bourne Again SHell” 的首字母縮寫， 所指的是這樣一個事實，bash 是最初 Unix 上由 Steve Bourne 寫成 shell 程式 sh 的增強版。
When using a graphical user interface, we need another program called a terminal emulator to interact with the shell. If we look through our desktop menus, we will probably find one. KDE uses konsole and GNOME uses gnome-terminal, though it’s likely called simply “terminal” on our menu. There are a number of other terminal emulators available for Linux, but they all basically do the same thing; give us access to the shell. You will probably develop a preference for one or another based on the number of bells and whistles it has.
當使用圖形使用者介面時，我們需要另一個和 shell 互動的叫做終端模擬器的程式。 如果我們瀏覽一下桌面選單，可能會找到一個。雖然在選單裡它可能都 被簡單地稱為 “terminal”，但是 KDE 用的是 konsole , 而 GNOME 則使用 gnome-terminal。 還有其他一些終端模擬器可供 Linux 使用，但基本上，它們都完成同樣的事情， 讓我們能訪問 shell。也許，你可能會因為附加的一系列花俏功能而喜歡上某個終端。
So Let's get started. Launch the terminal emulator! Once it comes up, we should see somehing like this:
好，開始吧。啟動終端模擬器！一旦它執行起來，我們應該看到一行像這樣的文字：
[me@linuxbox ~]$
This is called a shell prompt and it will appear whenever the shell is ready to accept input. While it may vary in appearance somewhat depending on the distribution, it will usually include your username@machinename, followed by the current working directory (more about that in a little bit) and a dollar sign.
這叫做 shell 提示符，無論何時當 shell 準備好了去接受輸入時，它就會出現。然而， 它可能會以各種各樣的面孔顯示，這則取決於不同的 Linux 發行版， 它通常包括你的使用者名稱@主機名，緊接著當前工作目錄（稍後會有更多介紹）和一個美元符號。
If the last character of the prompt is a pound sign (“#”) rather than a dollar sign, the terminal session has superuser privileges. This means either we are logged in as the root user or we selected a terminal emulator that provides superuser (administrative) privileges.
如果提示符的最後一個字元是“#”, 而不是“$”, 那麼這個終端會話就有超級使用者許可權。 這意味著，我們或者是以 root 使用者的身份登入，或者是我們選擇的終端模擬器提供超級使用者（管理員）許可權。
Assuming that things are good so far, Let's try some typing. Type some gibberish at the prompt like so:
假定到目前為止，所有事情都進行順利，那我們試著鍵入字元吧。在提示符下敲入 一些像下面一樣的亂七八糟的字元：
[me@linuxbox ~]$ kaekfjaeifj
Since this command makes no sense, the shell will tell us so and give us another chance:
因為這個命令沒有任何意義，所以 shell 會提示錯誤資訊，並讓我們再試一下：
bash: kaekfjaeifj: command not found
[me@linuxbox ~]$
If we press the up-arrow key, we will see that the previous command “kaekfjaeifj” reappears after the prompt. This is called command history. Most Linux distributions remember the last five hundred commands by default. Press the down-arrow key and the previous command disappears.
如果按下上箭頭按鍵，我們會看到剛才輸入的命令“kaekfjaeifj”重新出現在提示符之後。 這就叫做命令歷史。許多 Linux 發行版預設儲存最後輸入的500個命令。 按下下箭頭按鍵，先前輸入的命令就消失了。
Recall the previous command with the up-arrow key again. Now try the left and right-arrow keys. See how we can position the cursor anywhere on the command line? This makes editing commands easy.
可藉助上箭頭按鍵，來獲得上次輸入的命令。現在試著使用左右箭頭按鍵。 看一下怎樣把游標定位到命令列的任意位置？透過使用箭頭按鍵，使編輯命令變得輕鬆些。
While the shell is all about the keyboard, you can also use a mouse with your terminal emulator. There is a mechanism built into the X Window System (the underlying engine that makes the GUI go) that supports a quick copy and paste technique. If you highlight some text by holding down the left mouse button and dragging the mouse over it (or double clicking on a word), it is copied into a buffer maintained by X. Pressing the middle mouse button will cause the text to be pasted at the cursor location. Try it.
雖然，shell 是和鍵盤打交道的，但你也可以在終端模擬器裡使用滑鼠。X 視窗系統 （使 GUI 工作的底層引擎）內建了一種機制，支援快速拷貝和貼上技巧。 如果你按下滑鼠左鍵，沿著文字拖動滑鼠（或者雙擊一個單詞）高亮了一些文字， 那麼這些高亮的文字就被拷貝到了一個由 X 管理的緩衝區裡面。然後按下滑鼠中鍵， 這些文字就被貼上到游標所在的位置。試試看。
Note: Don’t be tempted to use Ctrl-c and Ctrl-v to perform copy and paste inside a terminal window. They don’t work. These control codes have different meanings to the shell and were assigned many years before Microsoft Windows.
注意： 不要在一個終端窗口裡使用 Ctrl-c 和 Ctrl-v 快捷鍵來執行拷貝和貼上操作。 它們不起作用。對於 shell 來說，這兩個控制程式碼有著不同的含義，它們在早於 Microsoft Windows （定義複製貼上的含義）許多年之前就賦予了不同的意義。
Your graphical desktop environment (most likely KDE or GNOME), in an effort to behave like Windows, probably has its focus policy set to “click to focus.” This means for a window to get focus (become active) you need to click on it. This is contrary to the traditional X behavior of “focus follows mouse” which means that a window gets focus by just passing the mouse over it. The window will not come to the foreground until you click on it but it will be able to receive input. Setting the focus policy to “focus follows mouse” will make the copy and paste technique even more useful. Give it a try. I think if you give it a chance you will prefer it. You will find this setting in the configuration program for your window manager.
你的圖形桌面環境（像 KDE 或 GNOME），努力想和 Windows 一樣，可能會把它的聚焦策略 設定成“單擊聚焦”。這意味著，為了讓視窗聚焦（變成活動視窗）你需要單擊它。 這與“聚焦跟隨著滑鼠”的傳統 X 行為不同，傳統 X 行為是指只要把滑鼠移動到一個視窗的上方。 它能接受輸入， 但是直到你單擊視窗之前它都不會成為前端視窗。 設定聚焦策略為“聚焦跟隨著滑鼠”，可以使拷貝和貼上更方便易用。嘗試一下。 我想如果你試了一下你會喜歡上它的。你能在視窗管理器的配置程式中找到這個設定。
Now that we have learned to type, Let's try a few simple commands. The first one is date. This command displays the current time and date.
現在，我們學習了怎樣輸入命令，那我們執行一些簡單的命令吧。第一個命令是 date。 這個命令顯示系統當前時間和日期。
[me@linuxbox ~]$ date
Thu Oct 25 13:51:54 EDT 2007
A related command is cal which, by default, displays a calendar of the current month.
一個相關聯的命令，cal，它預設顯示當前月份的日曆。
[me@linuxbox ~]$ cal
October 2007
Su Mo Tu We Th Fr Sa
1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30 31
To see the current amount of free space on your disk drives, type df:
檢視磁碟剩餘空間的數量，輸入 df:
[me@linuxbox ~]$ df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda2 15115452 5012392 9949716 34% /
/dev/sda5 59631908 26545424 30008432 47% /home
/dev/sda1 147764 17370 122765 13% /boot
tmpfs 256856 0 256856 0% /dev/shm
Likewise, to display the amount of free memory, type the free command.
同樣地，顯示空閒記憶體的數量，輸入命令 free。
[me@linuxbox ~]$ free
total used free shared buffers cached
Mem: 2059676 846456 1213220 0
44028 360568
-/+ buffers/cache: 441860 1617816
Swap: 1042428 0 1042428
We can end a terminal session by either closing the terminal emulator window, or by entering the exit command at the shell prompt:
我們可以透過關閉終端模擬器視窗，或者是在 shell 提示符下輸入 exit 命令來終止一個終端會話：
[me@linuxbox ~]$ exit
Even if we have no terminal emulator running, several terminal sessions continue to run behind the graphical desktop. Called virtual terminals or virtual consoles, these sessions can be accessed on most Linux distributions by pressing Ctrl- Alt-F1 through Ctrl-Alt-F6 on most systems. When a session is accessed, it presents a login prompt into which we can enter our user name and password. To switch from one virtual console to another, press Alt and F1-F6. To return to the graphical desktop, press Alt-F7.
即使終端模擬器沒有執行，在後臺仍然有幾個終端會話執行著。它們叫做虛擬終端 或者是虛擬控制檯。在大多數 Linux 發行版中，這些終端會話都可以透過按下 Ctrl-Alt-F1 到 Ctrl-Alt-F6 訪問。當一個會話被訪問的時候， 它會顯示登入提示框，我們需要輸入使用者名稱和密碼。要從一個虛擬控制檯轉換到另一個， 按下 Alt 和 F1-F6(中的一個)。返回圖形桌面，按下 Alt-F7。
To learn more about Steve Bourne, father of the Bourne Shell, see this Wikipedia article:
想了解更多關於 Steve Bourne 的故事，Bourne Shell 之父，讀一下這篇文章：
Here is an article about the concept of shells in computing:
這是一篇關於在計算機領域裡，shells 概念的文章：