How to update Slack on your Mac

1. Let Slack update itself. Open Slack. It checks for new versions on its own, and if it has not offered one yet, look in the Slack menu, or under Help or its preferences, for Check for Updates, then let it download and relaunch.
2. Upgrade the Homebrew cask. If you installed Slack with Homebrew, open Terminal and run brew upgrade --cask slack. Homebrew downloads the current build, checks it against the checksum it publishes and replaces the app in your Applications folder.
3. Or download it from slack.com. Otherwise get the current build from slack.com, which is the same download Homebrew points at. Quit Slack, open the download and put the new Slack in Applications in place of the old one: a disk image is dragged across, an installer package runs its own steps. Your settings and documents live outside the app and are kept.

brew upgrade --cask slack

That is one app. The same walk, through a different menu or page each time, is what every other app on the Mac asks of you, which is where Floodtide comes in.

Floodtide reads the same Homebrew record for Slack that the brew command above does, without needing Homebrew installed, to learn which version is current. When yours is behind, the row appears under Updates with the version it will move to and the download size. Pressing Update, or Update All, does the rest:

• The vendor's own build is downloaded, several apps at a time, with real progress.
• The download is verified against the checksum the catalogue publishes.
• Slack is asked to quit politely if it is open, and never forced.
• The bundle is swapped and the old version kept for seven days, so Undo Last Update always works.
• The replacement's code signature is checked; a build signed worse than the one you had is rolled back automatically.

Every download of Slack is checked against the checksum Homebrew publishes before anything is replaced.

If Slack lives in a folder macOS protects, the swap asks for your administrator password once for the whole batch, exactly as the Finder does when you install anything by hand.