Paths, case sensitivity, quoting, history and tab completion

Most beginner errors in the terminal come from four small things: being in a different folder than you thought, a wrong capital letter, a space in a name, or a typing slip in a long name. This lesson gives you a clear picture of each and three keyboard habits that remove most typing mistakes. It builds on the file-path ideas you met in the folders lesson.

The terminal is always somewhere

A graphical file manager shows you one folder at a time. The terminal works the same way, but it does not draw the folder. Instead, the shell remembers a current directory, also called the Working directory. When you give a command a name such as report.txt, the shell looks for it in the working directory unless you say otherwise. The prompt shows the working directory: ~ means your home folder, and ~/practice means a folder called practice inside it.

Imagine standing in a room of a house. If you say 'pass me the lamp', people assume you mean the lamp in this room. To mean a lamp in another room you must say which room. A command works the same way.

Absolute and relative paths

An Absolute path gives the complete route from the very top of the file system, which is written / and called the root. It always starts with a slash and works from anywhere, like a full postal address. A Relative path starts from where you are now, like saying 'next door, second house'. It does not start with a slash and only works from the right starting place.

Paths are used by every command that touches files. Compare the two commands below. Both do the same thing when you stand in /home/amina, but only the second works from every other folder. ls lists the contents of a folder.

ls practice
ls /home/amina/practice

Capital letters count

Linux is case sensitive: it treats Documents, documents and DOCUMENTS as three different names. The commands themselves are lower case. This surprises people used to Windows, which usually ignores capitals. If the folder is really called Documents and you type documents, the shell does not guess.

Spaces and quotes

The shell uses spaces to separate parts of a command. So if a folder is called My Notes, the command ls My Notes is read as two arguments: a folder My and a folder Notes. Neither exists, so you get two errors. To keep the name in one piece, wrap it in quotes. Quoting tells the shell: treat everything between the marks as a single item.

echo Hello      world
echo "Hello      world"

The first command prints Hello world with a single space, because the shell throws the extra spaces away when splitting the command into parts. The second keeps all the spaces because the quotes made one part. You can use straight double quotes "like this" or single quotes 'like this'. Use the plain quote keys on the keyboard, not curly quotes copied from a web page.

Three habits that save typing and mistakes

History. The shell remembers what you typed. Press the Up arrow to bring back the previous command, again for the one before, and Down arrow to go forward. Press Enter to run it, or edit it first with the left and right arrows. The command history prints the numbered list of earlier commands. Pressing Ctrl+R then typing a few letters searches backwards through that Command history.

Tab completion. Type the first few letters of a file or folder name and press Tab. If only one name starts with those letters, the shell completes it for you. If several do, press Tab twice to see the choices, type one more letter and press Tab again. This is Tab completion. It saves typing, and it also proves the name exists: if Tab adds nothing, you probably misspelt it or are in the wrong folder.

Ctrl+C. If a command is taking too long, producing endless output, or you started something by mistake, hold Ctrl and press C. This sends a request to stop the running command and returns you to the prompt. It does not copy text: inside a terminal, copy and paste use Ctrl+Shift+C and Ctrl+Shift+V. The command sleep 30 simply waits for 30 seconds, which makes it a harmless way to practise.