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luascreenmultiple-monitorsawesome-wm

I would like to open one program on the second screen in AwesomeWM, but only if the second screen is available

I made a change in my rc.lua to always open Chromium on screen 2:

awful.rules.rules = {
    -- many other rules here...

    -- Set Chromium to always map on screen "2"
    { rule = { class = "Chromium" },
      properties = { screen = 2 } },
}

However, when I do not have an external monitor attached, I get an error ("screen expected, got nil"). How do I modify this rule to use screen 1 if screen 2 is not available?

Solution

  • The following assumes you have only two or one screens. It does the wrong thing when there are more screens, but it should get the idea across:

    properties = { screen = function() return screen.count() end }

    All(?) properties in awful.rules can also be specified as a callback function. This function even gets the client (and the table of collected properties?) as argument (but this is not used in this example).