Epigraver - a macOS Screensaver

Epigraver is a macOS screensaver that repeatedly calls some command line program or script specified by the user and displays the textual output of that script on the screen. The transition from one output to the next is animated using one of several animations.

Originally the screensaver was just meant to display the output from the fortune program, but in its current iteration, it can call anything that puts some text on stdout and then terminates.

Installation

Head over to the releases section and get the DMG of the current release. Those DMGs are always notarized. The DMG contains the screensaver bundle and double-clicking on it will install it.

Configuration

Preparation

To make this screensaver display anything interesting other than the default "No command found", you need some command line program that generates texts. As it all started with fortune, let's assume that you want to use that. Unfortunately fortune isn't preinstalled on macOS, but it's pretty easy to install it via Homebrew. Run

brew install fortune

in your terminal application of choice. By default brew will install it in usr/local/bin. Be sure to note the full path to it if you made any adjustments to your Homebrew configuration. You'll need it in the next step.

Commands

In the preferences pane for screensavers open the preferences for Epigraver and there the Commands tab.

This is where you specify all the commands you want the screensaver to call.

The settings for each command are:

• Name: The name for the command. This is what you'll see in the command list in the schedule configuration
• Command: The command line to execute. zsh is used to execute it. You can just enter the full path to some command line program here - like /usr/local/bin/fortune in this example - or anything else that would work on a shell (e.g. date, time). Just like when you would run it in your terminal application, you can add command line parameters to use here. To have a fortune command that only displays offensive entries you would enter /usr/local/bin/fortune -o here
• Animation Interval: The interval at which the command is called again. Here it is called every 60 seconds.

The Test button executes the command once and displays the result in the preview below.

Appearances

On the appearances tab you can configure the font, the foreground and background color used by the screensaver. There are already 5 sets preconfigured. You can change them and add additional ones.

Schedule

Until now you may have wondered why you can specify multiple commands and appearances. Enter the schedule.

The schedule enables you to specify when what commands with which appearances and animations are executed. Let's go through the available options from top to bottom

• Time: Set the time range and weekdays for a schedule entry. Note that as a time range you can also specify something like 19:00 - 06:00. This would be a night entry that would be active from 7PM until 6AM on the next morning.
• WiFi Name: You can - but do not need to - specify the name of a WiFi network this entry is to be active on. The drop down menu contains the name of the current WiFi if you are currently using one. You can enter any name here though. One possible use for this is to create distinct schedule entries for when you are at the office, at home or some public place like your favorite coffee shop.
• Network Location: As with the previous, another way to have some kind of location awareness. The drop down menu lists all network locations configured in the network preferences pane. You can only choose from those because if it isn't configured there, it will never be active.
• Command: The command to use for a schedule entry. The list contains the names of all commands configured on the Commands tab.
• Appearances: Choose one or more appearances to use. When the screensaver is started it selects one random entry from your chosen appearances for the active schedule entry and uses that one for the whole run of the screensaver.
• Animations: There are several animations available for the transition from one output of the command to the next. The names give a rough indication of the kind of animation, but the best way to get to know them is to choose just one of them and then run the screensaver.

When Epigraver is started, it looks through the list of schedule entries from top to bottom and takes the first that matches the current situation. It's a good idea to have one generic catch all entry at the bottom and more specific entries further up in the list. A command, one appearance and one animation are chosen at the start of the screensaver. Even if another schedule entry would become active while the screensaver is running, it won't be chosen. The screensaver always sticks with the configuration it selected at the start.

Building the screensaver yourself

To give an in depth explanation of how you can build something in Xcode and how you can create the needed certificates is out of scope for this Readme. Let's assume that you already know your ways in Xcode and get to some specifics for Epigraver. I use a shell script to build a release of the screensaver, bundle it in a DMG and notarize that DMG. The script is called buildRelease.sh. To run it you need

• to have create-dmg installed. This is used to create the DMG

• have the environment variable EPIGRAVER_DMG_SIGNER set to the name of the developer id certificate you also use to build the screensaver. It would be better to extract it from the build logs, but I haven't tried to do that yet. So you need to set it explicitly here. It will be something of the form Developer ID Application: YOUR NAME (YOURTEAMID). If that enviroment variable is not set the script will build the release of the screensaver and bundle it in an unsigned DMG. This kind of DMG is fine if you just want to install the screensaver on the same computer the build is running

• have the environment variable EPIGRAVER_NOTARIZATION_KEYCHAIN_PROFILE set to the name of the keychain profile created with notarytool store-credentials. For more information about notarization with the notarytool see Customizing the Notarization Workflow

  Only if this variable is set, the DMG will be uploaded for notarization. The script also staples the DMG. You then have a notarized DMG that can be used to install the screensaver on any other macOS computer.

Acknowledgements

The DeveloperExcuses and Aerial screensavers helped me to understand how things work with screensavers.

As always, stackoverflow has been a source of needed advice and solutions to various challenges.