TL;DR: I built a free command replacement for macOS because I missed it from Linux. It’s open source and written in C.

The Problem

If you’ve spent any time on Linux, you’ve probably typed free -h hundreds of times. It’s the quickest way to check memory usage from the terminal.

Then you switch to macOS and… nothing.

$ free

zsh: command not found: free

Your options become:

Open Activity Monitor (requires leaving the terminal, unthincable…)
Run some obscure vm_stat command and do math
Write a janky shell script

None of these felt right.

The Solution

I decided to build mac-free - a native C utility that replicates the Linux free command on macOS.

$ free -h
              total        used        free      shared  buff/cache   available
Mem:         16.0Gi       8.0Gi       2.0Gi     512.0Mi       6.0Gi       8.0Gi
Swap:         2.0Gi     512.0Mi       1.5Gi

Looks familiar, right?

Features

Multiple output formats - bytes, KiB, MiB, GiB, or human-readable
Wide mode - shows macOS-specific categories (active, inactive, wired, compressed)
Continuous monitoring - watch memory usage with -s flag
Familiar options - compatible with common free command flags

Examples

Human-readable format:

$ free -h
               total         used         free       shared   buff/cache    available
Mem:          16.0Gi        8.0Gi        2.0Gi      512.0Mi        6.0Gi        8.0Gi
Swap:          2.0Gi      512.0Mi        1.5Gi

Wide output with all memory categories:

$ free -w -h
              total        used        free      active    inactive       wired  compressed   available
Mem:         16.0Gi       8.0Gi       2.0Gi       4.0Gi       2.0Gi       2.0Gi       1.0Gi       8.0Gi
Swap:         2.0Gi     512.0Mi       1.5Gi

Monitor memory every 2 seconds:

free -h -s 2

Show totals for RAM + swap:

$ free -h -t
              total        used        free      shared  buff/cache   available
Mem:         16.0Gi       8.0Gi       2.0Gi     512.0Mi       6.0Gi       8.0Gi
Swap:         2.0Gi     512.0Mi       1.5Gi
Total:       18.0Gi       8.5Gi       3.5Gi

How It Works

Under the hood, mac-free uses native macOS APIs:

host_statistics64() - retrieves VM statistics including page counts
sysctl() - gets total physical memory and swap usage
vm_page_size - system page size for converting pages to bytes

The tricky part was mapping Linux memory concepts to macOS equivalents:

Linux	macOS Equivalent
used	Active + Wired + Compressed
buff/cache	Inactive memory
available	Free + Inactive

macOS also has compressed memory - a feature where the system compresses inactive pages instead of swapping to disk. This shows up in wide mode.

Why C?

Honestly? I wanted an excuse to write some C again.

It had been a while since I’d worked with manual memory management, system calls, and Makefiles. This project was small enough to be fun but practical enough to actually use.

Plus, C felt appropriate for a system utility like this.

Installation

Full installation instructions (Homebrew or source) are available in the GitHub repository.

Requires Xcode Command Line Tools (xcode-select --install).

Lessons Learned

macOS memory management is different - No clear separation between buffers and cache like Linux. Had to make some approximations.
System APIs are well-documented - Apple’s developer docs made this easier than expected.
Simple tools are satisfying - Not everything needs to be a complex project. Sometimes a 500-line C program solves your problem perfectly.

Final Thoughts

This project reminded me why I love building small, focused tools. No frameworks, no dependencies, no complexity - just a straightforward solution to an everyday annoyance.

If you’re a Linux user on macOS missing your favorite commands, I encourage you to build your own. You might be surprised how approachable system programming can be.

The project is open source under MIT license. Contributions, issues, and stars are all welcome.

Now go check your memory usage!

free -mht

Tech Quests

(Mac)Free