Project 3: The Filesystem Explorer (ls -R) Clone

A robust clone of the ls command that supports recursion (-R) and detailed listing (-l). You will read directories, query file metadata (inodes), and handle permissions formatting.

Quick Reference

Attribute Value
Primary Language C
Alternative Languages Rust
Difficulty Level 2: Intermediate
Time Estimate Weekend
Knowledge Area Filesystem / Inodes
Tooling GCC, man pages
Prerequisites C structs, recursion.

What You Will Build

A robust clone of the ls command that supports recursion (-R) and detailed listing (-l). You will read directories, query file metadata (inodes), and handle permissions formatting.

Why It Matters

This project builds core skills that appear repeatedly in real-world systems and tooling.

Core Challenges

  • Directory Traversal: Using opendir, readdir, closedir.
  • Stat System Call: Converting stat struct data into human-readable strings (e.g., rwxr-xr-x).
  • Time Formatting: Handling Unix timestamps.
  • Recursion: Safely walking directory trees without infinite loops (symlinks).

Key Concepts

  • Inodes: struct stat and what it contains.
  • Directory Entries: struct dirent.
  • Bitmasks: Decoding permission bits (st_mode).

Real-World Outcome

$ ./myls -l
drwxr-xr-x  2 user group  4096 Dec 22 10:00 .
drwxr-xr-x 10 user group  4096 Dec 21 14:00 ..
-rw-r--r--  1 user group   512 Dec 22 10:01 main.c

Implementation Guide

  1. Reproduce the simplest happy-path scenario.
  2. Build the smallest working version of the core feature.
  3. Add input validation and error handling.
  4. Add instrumentation/logging to confirm behavior.
  5. Refactor into clean modules with tests.

Milestones

  • Milestone 1: Minimal working program that runs end-to-end.
  • Milestone 2: Correct outputs for typical inputs.
  • Milestone 3: Robust handling of edge cases.
  • Milestone 4: Clean structure and documented usage.

Validation Checklist

  • Output matches the real-world outcome example
  • Handles invalid inputs safely
  • Provides clear errors and exit codes
  • Repeatable results across runs

References

  • Main guide: LEARN_LINUX_UNIX_INTERNALS_DEEP_DIVE.md
  • “The Linux Programming Interface” by Michael Kerrisk