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