Sending automated reminders via a Slack webhook, AppleScript, and Launchd on MacOS

I have always enjoyed finding ways to automate processes, especially ones that don’t require much user interaction but just need to be done at a certain time or at regular intervals. At one of my first jobs out of high school, I wrote software to automate a job for one of the clients that normally took 2.5 days by hand, taking the process down to 30 minutes, including filling out all the paperwork. Of course, the company didn’t like losing those billable hours, but it was hard to argue with the efficiency.

At my church, we have a few computers with limited drive space. And that drive space always fills up fast! In the past, I would check the drives periodically and either delete old files or move them off to another storage place. I sat down recently and decided to take that a step further: I only wanted to be notified to check the drive when the drive was full to a certain threshold.

I’ve been playing around with Slack recently with a project I’m working on at home to notify me when my laundry is finished. If you’ve not heard of Slack, it is a collaboration/communication tool that integrates with lots of other platforms. It’s like a work-specific chatroom on steroids. One of the ways you can use it is with custom apps and webhooks, providing an easy way to send data and interact via a custom URL.

I won’t delve into setting up Slack and webhooks here, but I did want to share with you how I accomplished my goal to only get notifications when the drive is full to a certain amount. I used AppleScript and the Launchd framework built into MacOS.

If you’ve been on the Mac platform for awhile, you’ve no doubt heard of and have maybe used AppleScript. It’s a great way to interact with Mac apps and the system as a whole, so you can automate all kinds of things.

Launchd, as defined by Apple, is “a unified, open-source service management framework for starting, stopping and managing daemons, applications, processes, and scripts.” This framework is always working in the background on MacOS, whether you knew it or not!

So, I sat down and wrote an AppleScript that does the following:

  • Polls the system for the available space on the hard drive(s) I specified
  • If the space remaining is a certain amount or less, it sends a webhook request to my Slack app with a custom message to remind me to clear up the particular drive.

Screen Shot 2019-03-07 at 9.40.27 PM

Now, to schedule it. In the past, I used to use the built-in iCal/Calendar app for MacOS. It worked ok sometimes but I found that there were times scheduled events simply didn’t run for whatever reason. So, I decided to use a different method and take advantage of the Launchd process built into the operating system. There’s a lot you can learn about Launchd for MacOS, but I’ll summarize it here:

  • You can run processes as daemons, which run at the system level, not the user level
  • You can run processes as agents, which run at the user level
  • You can have them run when the system loads, or you can schedule them
  • Depending on where you place the file with the instructions about your script determines whether it runs as a daemon or agent

I chose to have mine run on a schedule every day at 7am, and send me an alert if the drive(s) are too full. I didn’t need it to run at the system level, so I made it an agent.

Screen Shot 2019-03-18 at 9.22.16 AM.png
This is the file that MacOS will look at to schedule the script to run.

Once I placed this file in my ~/Library/LaunchAgents/ folder (my main user account’s Launch Agents folder) and restarted the computer, it was ready to go! I’m looking forward to not having to remember to check those drive spaces manually anymore. I’ll automatically get notifications on my phone when I need to clear up space!

This is what the alert looks like on my phone.

I hope this helps you! If you want any of the scripts, they’re up on Github.

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