• How to use whoport
• Why? ps + grep falls apart with coding agents
• whoport under the hood
• Filling out your tool belt

Recently I’ve been running swarms of coding agents on my laptop. At some point I started to feel like my laptop is haunted, being puppeted by many beings out of my control.

For example, I’ll go to develop on jep, and run into:

% npm run dev

> dev
> react-router dev

Port 3000 is in use, trying another one...
  ➜  Local:   http://localhost:3001/
  ➜  Network: use --host to expose
  ➜  press h + enter to show help

Hey! Who is using localhost:3000 ?!

How to use whoport

whoport is my new small, sharp tool to solve this. Pass in a port and it’ll tell you what command (and therefore what path -> project + worktree) is using it:

% whoport 3000
PORT   PID      COMMAND
3000   68841    node /Users/cnord/dev/jep/node_modules/.bin/react-router dev

whoport can look up multiple ports at once:

% whoport 3000 5432
3000   68841    node /Users/cnord/dev/jep/node_modules/.bin/react-router dev
5432   688      /usr/local/opt/postgresql/bin/postgres -D /usr/local/var/postgres

Check it out here on GitHub 🐈‍⬛ https://github.com/cmnord/whoport

After you’ve found the process using your port, you can obviously kill -9 it 🔪 or otherwise shuffle ports around.

Why? ps + grep falls apart with coding agents

My previous tool for this was good ol’ ps with some text searches:

 Atuin v18.19.0                                                               <esc>: exit, <tab>: edit, <enter>: run, <ctrl-o>: inspect                                                        history count: 18631
  Search │ Inspect

  3 111ms   3mo ago ps aux | rg 'expo start'
  2 101ms   3mo ago ps aux | rg 'dev:'
  1 128ms   2mo ago ps aux | rg 'expo'
  > 123ms   2mo ago ps aux | rg 'expo '
 [     GLOBAL     ] 'ps aux'
 ps aux | rg 'expo '

shoutout to atuin

ps aux | rg 'npm ' worked when I had a hunch about the name of the command and I could search them. But now I have like 20-50 node processes running on my computer at any time…

% ps aux | rg 'node' | wc -l
      53
% ps aux | rg 'npm ' | wc -l
      28

And the commands agents kick off are completely unreadable…

% ps aux | rg 'npm ' | head -n 2
cnord            21752   0.1  0.4 446355296 149152   ??  S     8:02PM   0:00.22 node /Users/cnord/.nvm/versions/node/v22.22.3/bin/pnpm -C packages/editor exec vitest run --environment jsdom src/note/index.test.ts src/plugins/doc-change-listener.test.ts

↳ Okay, seems like it’s running Vitest, that’s fine.

cnord             6522   0.0  0.0 435341104   5136   ??  S     7:46PM   0:00.01 /usr/bin/open -n -W -o target/debug/example-dev.stdout.log --stderr target/debug/example-dev.stderr.log --env RANDOM_CONFIG_VAR=foo --env VITE_API_URL=https://api.example.com --env YOUR_SECRET_KEY=hunter2 --env YOUR_RANDOM_OAUTH_CLIENT_ID=hunter2 --env PATH=./my/whole/hecking/path/list/.bin:/......... target/debug/Example.app

↳ What in the world is happening in this 3,000-character command which has my whole env and PATH in it???

which of you is hogging my port?

whoport under the hood

whoport glues together ~two other tools: stalwart ps, plus lsof to list open files.

The core lsof command is:

lsof -t -nP -iTCP:"$port" -sTCP:LISTEN

Brief explanation of the command:

flag(s)	meaning
-t	terse output: PIDs only, no header
-nP	skip DNS resolution and service name lookups
-iTCP:$port	only TCP sockets using this port (local or remote)
-sTCP:LISTEN	only TCP sockets in listen state

So with just this command we can get a newline-separated list of process IDs (PIDs).

whoport turns this into a comma-separated list to hand to ps.

Heroic ps returns, instead filtering by PID instead of search on the commands!

% ps -o pid=68841,command=COMMAND -p 68841
68841 COMMAND
68841 node /Users/cnord/dev/jep/node_modules/.bin/react-router dev

Filling out your tool belt

I keep little scripts like this in my dotfiles repo, which documents my favorite terminal commands and setup across laptops and machines. 🛠️

You should too! Some influential blogs on this topic:

• Your Dotfiles Are Meant to be Forked, Zach Holman
• Managing Your Dotfiles, Anish Athalye

Read more about tiny personal programs here:

• Some tiny personal programs I’ve written, Julia Evans

And to learn more about the command line, ps, etc., I highly recommend The Missing Semester of Your CS Education.

Happy coding :)