Project 3: Implement popen() and pclose()

Your own implementation of the popen() and pclose() library functions.

Quick Reference

Attribute Value
Primary Language C
Alternative Languages N/A
Difficulty Level 3 (Advanced)
Time Estimate See main guide
Knowledge Area Library Implementation, Process Management
Tooling See main guide
Prerequisites See main guide

What You Will Build

Your own implementation of the popen() and pclose() library functions.

Why It Matters

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

Core Challenges

  • Bidirectional limitation → Why popen is read OR write, not both
  • Process tracking → Mapping FILE* to child pid for pclose()
  • Signal handling → What happens if child ignores SIGPIPE?

Key Concepts

  • Map the project to core concepts before you code.

Real-World Outcome

# Your implementation passes the same tests as the real popen
$ ./test_mypopen
Testing mypopen("ls", "r")...
  Read: file1.txt\nfile2.txt\n
  mypclose returned: 0
  PASS

Testing mypopen("cat", "w")...
  Wrote: "Hello from parent\n"
  mypclose returned: 0
  PASS

Testing mypopen("exit 42", "r")...
  mypclose returned: 42
  PASS (exit status preserved)

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: UNIX_IPC_STEVENS_VOL2_MASTERY.md
  • Primary references are listed in the main guide