Command line and power tools

Folders that act

Updated 2026-07-31 · 4 min read

A folder that files its own contents is the cheapest automation a Mac offers.

Folder Actions, the built-in route

1. Automator → New → Folder Action
2. Choose the folder it watches
3. Stack actions: Rename Finder Items, Move Finder Items, Run Shell Script…
4. Save; it runs on every arrival

Manage attachments later: right-click a folder → Services → Folder Actions Setup.

The classic recipes

• Downloads sorter: watch Downloads; move .dmg/.pkg to an Installers folder, PDFs

to Documents/Inbox

• Screenshot filer: watch the screenshot folder; rename with date, move to

Pictures/Screenshots

• Print-to-PDF inbox: watch a PDFs folder; run ocrmypdf or rename by date
• Drop-to-convert: watch a folder; run a shell script over anything dropped

(imagemagick resize, ffmpeg transcode)

A shell script action, sketched

In Automator's Run Shell Script (pass input as arguments):

for f in "$@"; do
  case "$f" in
    *.dmg|*.pkg) mv "$f" "$HOME/Downloads/Installers/" ;;
    *.pdf)       mv "$f" "$HOME/Documents/Inbox/" ;;
  esac
done

launchd for the serious version

Folder Actions occasionally sleep through events. A LaunchAgent with WatchPaths is the robust equivalent — a plist in ~/Library/LaunchAgents pointing at a script, triggered on any change to the watched path. More setup, complete reliability.

The caution

Automation acting on arrival meets half-downloaded files. Good recipes either match final extensions only (browsers download to .download/.crdownload first) or wait: a sleep 2 at the top of a script forgives most races. And never auto-delete — auto-*move* keeps mistakes recoverable.

Common questions

What are Folder Actions on a Mac?

Automator workflows attached to a folder, run automatically when items are added to it.

Why does my folder action fire before the download finishes?

Browsers write temp files first. Match only final extensions, or start scripts with a short sleep.