🍎 macOS Tricks

A running collection of macOS hints: small tools and incantations that each solve one annoyance well, and are each too short to deserve their own page. Entries stand alone — read the one you need and ignore the rest.

duti — set default apps from the CLI

duti manages file-type → app associations. It does what Finder’s Open With → Change All… does, except scriptable, and therefore repeatable across machines.

Associations are per-user. Run it as the account whose defaults are changing, not under sudo.

brew install duti
# for another account: su - guidos -c 'brew install duti'

Find the identifiers

Setting an association takes two things: the app’s bundle ID, and the file’s Uniform Type Identifier.

osascript -e 'id of app "Zed"'               # app bundle ID
mdls -name kMDItemContentType -r file.json   # a file's UTI
duti -x json                                 # who currently handles .json

Set the default

duti -s dev.zed.Zed public.json all          # by UTI
duti -s dev.zed.Zed jsonl all                # by extension, for odd or dynamic types
duti -s abnerworks.Typora net.daringfireball.markdown all

The trailing argument is the role — all, viewer, or editor. Use all unless there’s a specific reason not to.

Common UTIs

UTI	Extension
public.json	.json
public.plain-text	.txt
net.daringfireball.markdown	.md
public.yaml	.yaml, .yml
public.shell-script	.sh
public.data	fallback for unknown types

Keep it in dotfiles

The calls are idempotent, so a batch is safe to rerun and belongs with your dotfiles — a new machine then gets the same associations without a Finder session.

duti -s dev.zed.Zed public.plain-text all
duti -s dev.zed.Zed public.yaml all
duti -s dev.zed.Zed public.shell-script all

Changes hit the LaunchServices database for the current user only, and take effect immediately — no restart, no logout. The Finder equivalent, one file type at a time, is ⌘I → Open with → Change All….