Course 02 — The command line

The terminal,without the fear.

Every engineer lives in a terminal eventually. Here you learn it on a file system you can see: folders grow as you make them, files fly when you move them, and data visibly flows through a pipeline.

Start lesson one Open the sandbox

15 lessons · 6 chapters · free

Command line — building a project, then searching it
  1. 01 · Read

    Each lesson is one idea, explained in a few short paragraphs — no walls of theory.

  2. 02 · Do

    Type into a live environment and watch it react. Tab completes, ↑ recalls, undo takes back any step.

  3. 03 · Match

    Reach the goal any way you like — you're judged on the result, not the keystrokes. Par is the shortest route.

01

Finding your way

Where you are, what's here, and how to get somewhere else.

  1. 01 Look around Where am I, what's here, and how do I go somewhere else?
  2. 02 Paths: absolute, relative and .. Getting anywhere in one command.
  3. 03 Hidden files Files that start with a dot don't show up — until you ask.
02

Making things

Create, copy, move and delete files and folders.

  1. 04 Make folders and files mkdir, mkdir -p, and touch.
  2. 05 Copy and move cp duplicates, mv relocates — and renames.
  3. 06 Delete — carefully rm, rm -r, and why there's no undo.
03

Reading files

Look inside files without opening an editor.

  1. 07 Peek inside files cat, head and tail — without opening an editor.
  2. 08 Count lines, words and bytes wc, the quickest answer to "how big is this?"
04

Pipes & redirection

Send one command's output into another, or into a file.

  1. 09 Write output to a file > replaces, >> appends.
  2. 10 Pipes: one command into the next The idea the whole Unix toolbox is built on.
  3. 11 A real pipeline: top visitors cut, sort and uniq — counting things like a data engineer.
05

Searching

Find files by name and lines by content.

  1. 12 Search inside files grep -r: every match, everywhere.
  2. 13 Find files by name find, and acting on what it finds.
06

Permissions

Who can read, write and run what.

  1. 14 Run a script Permission denied, chmod +x, and ./
  2. 15 Lock a file down Octal permissions: 600, 644, 755.

The shell is simulated — a faithful subset of bash and the standard Unix tools, on an in-memory file system. Nothing touches your computer, so rm -rf is perfectly safe to try.