The shell

Ordering food at a restaurant, you can point at pictures on the menu (clicking around a screen), or you can tell the waiter exactly what you want: “a large margherita, extra basil, no olives.” Pointing is easy to start with. Talking is faster, more precise, and lets you ask for things that aren’t on the pictures.

The shell is talking to your computer. Instead of double-clicking folders, you type short commands. It looks old-fashioned, but almost every professional programmer uses it every day, because it’s fast, precise, and you can automate anything you can type.

Don’t worry: everything in this lesson happens in a pretend computer inside the page. You can’t break anything, so explore freely.

The real words

• A shell (terminal) is a program that reads commands you type and runs them. The window it runs in is called the terminal. Common shells: bash (Linux, older Macs), zsh (modern Macs), PowerShell (Windows).
• The prompt (like you@crayon:~$) shows who you are and which folder you’re in, and waits for a command.
• Command anatomy: ls -l notes: the command (ls), options or flags that change how it behaves (-l for “long”), and arguments (notes, what to act on).
• pwd, ls, cd:
  • pwd (print working directory): the folder you’re in right now.
  • ls (list): what’s in this folder. ls -l shows details; ls -a also shows hidden files (names starting with .).
  • cd path (change directory): move to another folder.
• A path is an address for a file or folder:
  • Absolute paths start at the very top, /: /home/you/notes/todo.txt.
  • Relative paths start from where you are: notes/todo.txt.
  • Shortcuts: ~ = your home folder, . = this folder, .. = the folder above.
• Help: man ls (the manual) or ls --help on a real computer. In our pretend shell, type help.
• Time savers: press Tab to auto-complete names, and the ↑ arrow to bring back earlier commands.