LinuxLingo
LinuxLingo is a command-line application for learning Linux commands through an interactive shell simulator and a built-in quiz system. It is designed for Computer Science students who want to build confidence with the Linux command line by typing real commands, seeing real output, and testing their knowledge — all within a safe, in-memory virtual file system (VFS) that never touches real files.
See the GitHub repo for full source code, documentation, and releases.
Architecture
The application is organized into five main components:
| Component | Responsibility |
|---|---|
| CLI | Handles user I/O (Ui) and top-level command dispatch (MainParser) |
| Shell | Parses and executes shell commands in a simulated Linux environment |
| Exam | Manages exam sessions — question presentation, answer checking, scoring |
| Storage | Reads/writes data on the real file system (question banks, VFS snapshots) |
| VFS | In-memory virtual file system that all shell commands operate on |
Shell Simulator
The Shell Simulator provides a Linux-like command-line environment backed by an in-memory VFS. All file and directory operations are performed within this VFS — no real files are created, modified, or deleted.
36 supported commands across 8 categories:
| Category | Commands |
|---|---|
| Navigation | cd, ls, pwd |
| File Operations | mkdir, touch, rm, cp, mv, cat, echo, diff, tee |
| Text Processing | head, tail, grep, find, wc, sort, uniq |
| Permissions | chmod |
| Information | man, tree, which, whoami, date |
| Alias & History | alias, unalias, history |
| Environment | save, load, reset, envlist, envdelete |
| Utility | help, clear |
Advanced shell features:
- Piping (
|), output redirection (>,>>), input redirection (<) - Command chaining with
&&,||, and; - Glob expansion (
*,?) against the VFS - Variable expansion (
$USER,$HOME,$PWD,$?) - Alias resolution with circular-reference protection
- Tab completion and command history (via JLine 3)
- Typo suggestions using Levenshtein edit distance
Shell Parsing Pipeline
The parser transforms raw input into a structured ParsedPlan through two stages:
- Tokenization — a char-by-char state machine with three states (
NORMAL,IN_SINGLE_QUOTE,IN_DOUBLE_QUOTE) that recognizes operators, quotes, and escape sequences. - Plan Building — groups tokens into
Segmentobjects separated by operators, each segment holding a command name, arguments, and optional redirect information.
The execution engine (ShellSession.runPlan()) iterates the plan, chaining stdout/stdin across pipe boundaries, and evaluating &&/|| conditions based on exit codes.
Exam System
The exam module supports three question types:
| Type | Description |
|---|---|
| MCQ | Multiple-choice questions on Linux concepts |
| FITB | Fill-in-the-blank questions |
| PRAC | Practical questions — user types real shell commands in a temporary VFS; answer is verified by checking VFS state against Checkpoint objects |
Exam sessions can be started interactively (topic selection prompt), directly via CLI args (exam -t navigation -n 5), or as a single random question (exam -random).
VFS Design
- Tree structure of
FileNodeobjects —Directoryuses aLinkedHashMapfor ordered, O(1) lookup by name. Permissionmodels Unix 9-character permission strings, supporting both octal and symbolicchmodnotation.deepCopy()at every level enables snapshot-based features (saving/loading environments, isolated PRAC exam VFS instances).- All path operations go through
VirtualFileSystem— shell commands never usejava.ioorjava.nio.filefor simulated files.