How to run script on OS theme change

[Crocmagnon]

I'd like to run a shell command on OS theme change, to update fish's color scheme.
In iTerm2, I can achieve this using their "scripts" feature. I documented my process here: https://gabnotes.org/terminal-dark-light-mode/
Is there a way to achieve the same thing in Ghostty?
I read #2755, but I'm unsure how I can use the information in there.

[leigholiver]

This might be outside of the scope of Ghostty as there is already the option to change the Ghostty theme based on the OS theme (light:theme-name,dark:theme-name), and you probably want to hook into the os theme directly. Assuming you're on macos you might be able to add something like this to your fish config and hook into your existing functions:

function check_system_theme
    set -g SYSTEM_THEME (defaults read -g AppleInterfaceStyle 2>/dev/null)
    if test $status -eq 0
        fish -c dark
    else
        fish -c light 
    end
end

# Run on shell start and create a periodic check
check_system_theme

Not a fish user though im afraid so I cant test it, grain of salt :D

[Crocmagnon]

I’d prefer an option to react to an event instead of actively polling the settings.

[leigholiver]

Fair - you might be able to do something like this, where defaults read-type just blocks until the value changes

function watch_theme_changes
    while true
        # Get current theme
        set current_theme (defaults read -g AppleInterfaceStyle 2>/dev/null || echo "Light")
        
        # Watch for changes using defaults read-type
        defaults read-type -g AppleInterfaceStyle >/dev/null 2>&1
        
        # Get new theme after change
        set new_theme (defaults read -g AppleInterfaceStyle 2>/dev/null || echo "Light")
        
        if test "$current_theme" != "$new_theme"
            echo "Theme changed from $current_theme to $new_theme"
            # Add your custom actions here
        end
    end
end

again grain of salt - not a fish/macos user

[Crocmagnon]

A couple of issues:

• defaults read-type doesn't block, it returns the type of the variable
• the variable may not exist if in light mode

Both your answers look AI generated 😕 If they are, please consider not posting them - I can ask chatgpt myself if I need to. In the contrary, please disregard this comment 🙂
Thank you for your enthusiasm though!

[Crocmagnon]

After doing more research, I gave up and wrote a swift program to listen to the OS theme and trigger the fish shell command:

https://github.com/Crocmagnon/os-theme-detector

I would find it much simpler if Ghostty provided a native way of doing this without requiring building these blocks, since it's already a swift app and it's already aware of the OS theme change.

At least this is terminal-agnostic.

[Crocmagnon]

Intentionally not marking this as the answer because I don't find it satisfying.

[jcollie]

It wouldn't be terribly difficult to have Ghostty run a command when the theme changes, but that's only the easy part. First of all, does Ghostty run it in the right environment to talk to the rest of your shells? Second, how do you notify all of your shells and other applications to update? There's a lot there that's really out of scope for Ghostty.

[Crocmagnon]

how do you notify all of your shells and other applications to update

fish handles this with universal variables. My light/dark functions take advantage of them and work as expected. A single run in a single shell and all other are notified that the theme has changed.

does Ghostty run it in the right environment to talk to the rest of your shells?

Not sure I understand

that's only the easy part

That's the only part I need 😛