The terminal

Linux runs most of the world's servers, phones (Android is built on it) and a lot of laptops. You can use it with a mouse, but the real power is in the command line: a window where you type commands and the computer answers in text.

The window is the terminal. The program inside it that reads what you type is the shell; on most systems it's Bash, and macOS uses a close cousin, zsh. Everything in this course works in both.

The shell shows a prompt when it's ready, something like sam@laptop:~$. That's your user name, the computer's name, the folder you're in (~ means your home folder) and a $ that means "type here". In the examples, the $ is the prompt: type what comes after it, then press Enter.

$ whoami
sam
$ echo Hello, duck
Hello, duck

A command is a program name, then options, then arguments, separated by spaces. In ls -l Documents, ls is the program (list files), -l is an option that changes how it works (the long, detailed list) and Documents is the argument it works on. Short options are a dash and a letter, and you can bunch them: ls -l -a is the same as ls -la. Long options use two dashes, like --help.

Commands are case-sensitive: ls works, LS doesn't. Most commands print nothing when they succeed, so silence usually means it worked.