A safety guard that teaches: Arc Academy Terminal 1.1

The command line is one of the most durable skills in computing and one of the worst taught. Documentation assumes you already know it. Tutorials send you into a real shell, where a mistyped rm has real consequences. So most people learn just enough to copy commands they do not understand, and stop there.

Arc Academy Terminal is our answer: an open-source terminal application that teaches the shell by letting you actually use it. Version 1.1 makes practicing on real files safe by putting two different jobs in two different places.

Two ways to practice

Some learners want zero risk. For them there is a simulated shell. Arc Academy acts out every command itself inside its own practice folder, so nothing runs on the rest of the computer. It still handles quotes, variables, wildcards, pipes, redirection and scripts.

But a simulation only goes so far. Real files have real permissions, real paths and real output, and learning on them is what makes the skill stick. So Arc Academy also offers real-files lessons: each one runs in its own folder of starter files, and you work on it with a real shell.

Enforcement belongs where commands run

A program that reads a command before it runs can only guess what the command will do. Scripts, wildcards and variables decide that at the moment the shell runs them. So in Arc Academy the line that keeps a learner's commands inside their folder is not drawn by Arc Academy. It is drawn by the operating system.

Every real-files command runs inside the operating system's own sandbox: sandbox-exec on macOS, bubblewrap on Linux. Inside it, a command can change only its practice folder and a private temporary folder. It cannot use the network, and it cannot read the usual places keys and credentials are kept, such as SSH and GPG keys, cloud and developer logins, and the macOS keychain. The only settings it inherits from the learner's session are basics such as PATH and HOME, so API keys kept in environment variables stay out too. Before offering a real-files lesson, Arc Academy checks that the sandbox actually holds on that machine. Where it does not, real-files lessons are not offered.

Explanation belongs where the learner is

The sandbox makes the playground safe. It does not teach anything. A command that fails with "operation not permitted" tells a beginner only that the tool seems broken.

So Arc Academy keeps a guard in front of the shell as well, and its job is to explain. Commands that would wipe a disk or delete everything are refused, and the refusal says plainly what the command would have done. Type rm -rf / and you are told that it would delete everything from the root of the filesystem, with no confirmation and no undo. Then you carry on: the next command works, the lesson moves forward, and the file-management lesson teaches the habit that replaces it, rm -i, which asks before each deletion.

That loop (try, get stopped, understand why, do it properly) is how people learn to use dangerous tools in every other field. We wanted the command line to work the same way.

What else is in 1.1

• Forty lessons in two tracks. Explorer is ten story lessons for younger learners, from pwd to a first script. Operator is thirty lessons, from navigation and permissions through pipelines, find, sed, scripts and their arguments, SSH keys and Git.
• A live explanation of every command you run, and an optional AI helper that is off unless you choose it and works with the model provider you pick, including local models.
• Streaks, badges, mastery for each track, and a printable certificate when a track is finished.
• Lessons written as plain TOML files, so a teacher can add their own material.
• Progress is stored on your machine.

Try it

curl -fsSL https://arcacademy.sh/install.sh | sh

The installer downloads a prebuilt build for macOS or Linux and checks it against its published SHA-256 sum. The source is on GitHub under GPL-2.0, and the project site is arcacademy.sh.