WIR - What Is Running: A CLI Tool in C to Inspect Processes and Ports

I recently released wir (What Is Running), a command-line tool written in C to inspect what's running on specific ports and get detailed process information. A project born from a practical need that turned into an opportunity to explore system programming in C.

The Problem

How many times have you had a port occupied without knowing which process is using it? Or needed to trace a process hierarchy to understand who spawned what? We usually resort to combinations of lsof, netstat, and ps, but why not have everything in a single command?

The Solution

wir is a cross-platform tool (macOS and Linux) that allows you to:

• Discover which process is using a specific port
• Get detailed information about a PID
• Visualize the complete ancestry tree of a process
• List all running processes
• View a process's environment variables
• Output in normal, short, JSON, or tree format
• Receive security warnings for potentially risky configurations

Practical Examples

# Who's using port 8080?
wir --port 8080

# Info about a specific process
wir --pid 1234

# Show the process ancestry tree
wir --pid 1234 --tree

# JSON output for scripting
wir --port 3000 --json

# List all processes (short format)
wir --all --short

# Security warnings only
wir --port 8080 --warnings

The Architecture

The project is structured in a modular way:

• Platform abstraction layer: handles differences between Linux (/proc parsing) and macOS (libproc and sysctl)
• Output formatting: supports multiple display modes without duplicating logic
• Consistent error handling: every allocation is checked, every resource is freed
• Strict memory management: no leaks, no undefined behavior

What I Learned

Writing wir was an excellent opportunity to practice fundamental concepts:

1. System programming: interfacing with /proc, system calls, process management
2. Cross-platform development: conditional compilation and different APIs for each OS
3. Memory safety in C: manual memory management without a garbage collector
4. Build systems: Makefile with automatic platform detection
5. API design: clean and composable interface

I Don't Memorize Commands

As my approach goes: I'm not interested in memorizing the exact lsof or netstat commands. I prefer understanding the underlying architecture and building tools that solve the problem more elegantly. wir isn't just a wrapper, it's an abstraction that hides the complexity of OS differences.

The Future

The project is open to extensions:

• UDP port support
• Advanced process filtering
• Support for other OSes (BSD, etc.)
• Performance optimizations
• Additional output formats

Try It Out

wir

It's a learning project, so feel free to experiment and extend it. Building system tools in C is a great way to understand what's really happening under the hood.

# Build and install
brew tap AlbertoBarrago/tap
brew install wir

# Start using it
wir --port 3000