Folder Actions are one of many hidden gems in macOS. You can set an action to occur whenever the contents of a folder are changed. This can be a simple action drawn from a list that Apple provides with macOS, an AppleScript, or a workflow produced in Automator. Automator lets you extend these actions into Terminal shell scripts and other languages.
You can use Folder Actions for a lot of disparate purposes:
Resize images or convert them another file format when they’re added to a folder.
Provide a popup alert when items are added to a folder through an automated process that you otherwise wouldn’t know had completed.
Add a downloaded MP3 to the Music app.
Control-click any folder in the Finder and choose Services > Folder Actions Setup in Monterey. In early versions of macOS, the option appears in the main lists of contextual items. To avoid the malicious and accidental installation of Folder Actions, macOS requires a confirmation step that can’t be automated: click Run Service in the Confirm Service dialog. This adds the current folder to the Folders with Actions list without adding actions.
The Folder Actions Setup window appears with a dialog already open that reads Choose a Script to Attach. This list includes ones that Apple seeded, locating them inside the /Library/Scripts/Folder Actions Scripts folder. Any scripts installed by apps or that you’ve created and placed inside your Home directory’s ~/Library/Scripts/Folder Actions Scripts folder appear as well.
Folder Actions Setup shows all folders macOS is watching. Select any folder to see which scripts are attached. You can use checkboxes to toggle scripts on or off and folder watching for each folder on or off.
You can create Folder Actions in a numbers of ways:
Use an item Apple provides in the dialog that appears when you invoke Folder Actions Setup. These mostly relate to image processing.
You can use AppleScript as a simple bit of connective tissue, too. For instance, I have a workflow in Flying Meat’s Retrobatch Pro image-processing software that puts a border around an image. A simple AppleScript turns a folder into a spring-loaded passthrough for the Retrobatch Pro operation.
If you need more sophisticated watched-folder behavior, turn to Hazel from Noodlesoft, a supercharged third-party version of Folder Actions.
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