Jesse Grosjean (@jessegrosjean.bsky.social)

It’s been a while since I offered a shell trick, so here’s one I’ve found useful lately. It’s a way to quickly check what’s listening on a specific port. There are times when I run into a conflict running local services, saying the port is already in use, but I don’t know by what. So I use the following. This snippet relies on having your root password stored in your login keychain. See <a href="https://brettterpstra.com/2021/04/06/scripting-with-sudo-on-mac/">this post</a> for instructions on setting this up. Once it’s in place, you’ll have a secure way to run sudo commands from scripts which only ask for a password when your keychain is locked. Here’s the snippet, ready to use in a function or alias: <div class="language-bash highlighter-rouge"><div class="highlight"><pre class="highlight fixed"><code>#!/bin/bash PASS=$(security find-generic-password -l "root password" -a root -w|tr -d '\n') echo $PASS | sudo -S lsof -nP -iTCP:$1 -sTCP:LISTEN</code></pre></div></div> The snippet uses <a href="https://manpages.org/lsof/8" title="lsof (8): list open files">lsof</a> to show the process listening on whichever port you provide as the argument to the script. Store this in a function or script called <code class="language-plaintext highlighter-rouge">whatsonport</code> (or whatever you like). Replace <code class="language-plaintext highlighter-rouge">"root password"</code> with whatever you named your password entry in Keychain Access. Now you can call it like <code class="language-plaintext highlighter-rouge">whatsonport 2020</code>. I use this in Fish as a function in <code class="language-plaintext highlighter-rouge">~/.config/fish/functions/whatsonport.fish</code>: <pre><code class="language-fish">function whatsonport --description 'find out what PID is running on a port (requires password)' set -l pass (security find-generic-password -l "root password" -a root -w|tr -d '\n') echo $pass | sudo -S lsof -nP -iTCP:$argv -sTCP:LISTEN end </code></pre> Hope that’s useful! https://brettterpstra.com/2024/12/16/shell-tricks-check-whats-listening-on-a-port/?utm_campaign=blog_post&utm_source=mastodon