Project 4: Minimal Terminal Emulator (100 Lines)

The smallest possible functional terminal emulator—just PTY handling and stdin/stdout forwarding, no escape sequence processing.

Quick Reference

Attribute Value
Primary Language C
Alternative Languages Go, Rust
Difficulty Level 2: Intermediate (The Developer)
Time Estimate 3-5 days
Knowledge Area Terminal Emulation / System Programming
Tooling Minimal Terminal
Prerequisites Projects 1-3

What You Will Build

The smallest possible functional terminal emulator—just PTY handling and stdin/stdout forwarding, no escape sequence processing.

Why It Matters

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

Core Challenges

  • PTY setup → The complete sequence to create a working terminal
  • I/O multiplexing → select/poll/epoll to handle bidirectional data
  • Non-blocking I/O → Don’t block on either end
  • Signal handling → SIGCHLD when shell exits, SIGWINCH for resize
  • Proper cleanup → Close FDs, wait for child

Key Concepts

Real-World Outcome

$ ./miniterm

# This is a real shell running in your terminal emulator!
$ ls
Documents  Downloads  file.txt
$ vim test.txt    # vim works!
$ htop            # htop works! (kind of - no escape processing yet)
$ exit

[miniterm] Shell exited with status 0
$

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: TERMINAL_EMULATOR_DEEP_DIVE_PROJECTS.md
  • “The Linux Programming Interface” by Michael Kerrisk