Writing your eww configuration

(For a list of all built-in widgets (i.e. box, label, button), see Widget Documentation.)
Eww is configured using its own language called yuck. Using yuck, you declare the structure and content of your widgets, the geometry, position, and behavior of any windows, as well as any state and data that will be used in your widgets. Yuck is based around S-expressions, which you may know from lisp-like languages. If you're using vim, you can make use of yuck.vim for editor support. If you're using VSCode, you can get syntax highlighting and formatting from yuck-vscode. It is also recommended to use parinfer, which makes working with S-expressions delightfully easy!

Additionally, any styles are defined in CSS or SCSS (which is mostly just slightly improved CSS syntax). While eww supports a significant portion of the CSS you know from the web, not everything is supported, as eww relies on GTK's own CSS engine. Notably, some animation features are unsupported, as well as most layout-related CSS properties such as flexbox, float, absolute position or width/height.

To get started, you'll need to create two files: eww.yuck and eww.scss (or eww.css, if you prefer). These files must be placed under $XDG_CONFIG_HOME/eww (this is most likely ~/.config/eww).

Now that those files are created, you can start writing your first widget!

Creating your first window

Firstly, you will need to create a top-level window. Here, you configure things such as the name, position, geometry, and content of your window.

Let's look at an example window definition:

(defwindow example
           :monitor 0
           :geometry (geometry :x "0%"
                               :y "20px"
                               :width "90%"
                               :height "30px"
                               :anchor "top center")
           :stacking "fg"
           :reserve (struts :distance "40px" :side "top")
           :windowtype "dock"
           :wm-ignore false
  "example content")

Here, we are defining a window named example, which we then define a set of properties for. Additionally, we set the content of the window to be the text "example content".

You can now open your first window by running eww open example! Glorious!

defwindow-properties

PropertyDescription
monitorWhich monitor this window should be displayed on. See below for details.
geometryGeometry of the window.

monitor-property

This field can be:

  • the string <primary>, in which case eww tries to identify the primary display (which may fail, especially on wayland)
  • an integer, declaring the monitor index
  • the name of the monitor
  • a string containing a JSON-array of monitor matchers, such as: '["<primary>" "HDMI-A-1" "PHL 345B1C" 0]'. Eww will try to find a match in order, allowing you to specify fallbacks.

geometry-properties

PropertyDescription
x, yPosition of the window. Values may be provided in px or %. Will be relative to anchor.
width, heightWidth and height of the window. Values may be provided in px or %.
anchorAnchor-point of the window. Either center or combinations of top, center, bottom and left, center, right.

Depending on if you are using X11 or Wayland, some additional properties exist:

X11

PropertyDescription
stackingWhere the window should appear in the stack. Possible values: fg, bg.
wm-ignoreWhether the window manager should ignore this window. This is useful for dashboard-style widgets that don't need to interact with other windows at all. Note that this makes some of the other properties not have any effect. Either true or false.
reserveSpecify how the window manager should make space for your window. This is useful for bars, which should not overlap any other windows.
windowtypeSpecify what type of window this is. This will be used by your window manager to determine how it should handle your window. Possible values: normal, dock, toolbar, dialog, desktop. Default: dock if reserve is specified, normal otherwise.

Wayland

PropertyDescription
stackingWhere the window should appear in the stack. Possible values: fg, bg, overlay, bottom.
exclusiveWhether the compositor should reserve space for the window automatically. Either true or false.
focusableWhether the window should be able to be focused. This is necessary for any widgets that use the keyboard to work. Either true or false.
namespaceSet the wayland layersurface namespace eww uses. Accepts a string value.

Your first widget

While our bar is already looking great, it's a bit boring. Thus, let's add some actual content!

(defwidget greeter [?text name]
  (box :orientation "horizontal"
       :halign "center"
    text
    (button :onclick "notify-send 'Hello' 'Hello, ${name}'"
      "Greet")))

To show this, let's replace the text in our window definition with a call to this new widget:

(defwindow example
           ; ... values omitted
  (greeter :text "Say hello!"
           :name "Tim"))

There is a lot going on here, so let's step through this.

We are creating a widget named greeter. This widget takes two attributes, called text and name. The declaration ?text specifies that the text-attribute is optional, and can thus be left out. In that case, its value will be the empty string "". The name attribute must be provided.

Now we declare the body of our widget. We make use of a box, which we set a couple attributes of.

We need this box, as a widget definition can only ever contain a single widget - otherwise, eww would not know if it should align them vertically or horizontally, how it should space them, and so on. Thus, we wrap multiple children in a box. This box then contains a reference to the provided attribute text, as well as a button. In that button's onclick attribute, we refer to the provided name using string-interpolation syntax: "${name}". This allows us to easily refer to any variables within strings. In fact, there is a lot more you can do within ${...} - more on that in the chapter about the expression language.

To then use our widget, we call it just like we would use any other built-in widget and provide the required attributes.

As you may have noticed, we are using a couple predefined widgets here. These are all listed and explained in the widgets chapter.

Rendering children in your widgets

As your configuration grows, you might want to improve the structure of your config by factoring out functionality into basic reusable widgets. Eww allows you to create custom wrapper widgets that can themselves take children, just like some of the built-in widgets like box or button can. For this, use the children placeholder:

(defwidget labeled-container [name]
  (box :class "container"
    name
    (children)))

Now you can use this widget as expected:

(labeled-container :name "foo"
  (button :onclick "notify-send hey ho"
    "click me"))

You can also create more complex structure by referring to specific children with the nth-attribute:

(defwidget two-boxes []
  (box
    (box :class "first" (children :nth 0))
    (box :class "second" (children :nth 1))))

Adding dynamic content

Now that you feel sufficiently greeted by your bar, you may realize that showing data like the time and date might be even more useful than having a button that greets you.

To implement dynamic content in your widgets, you make use of variables.

These user-defined variables are globally available from all of your widgets. Whenever the variable changes, the value in the widget will update!

There are four different types of variables: basic, polling, listening, and a set of builtin "magic" variables.

Basic variables (defvar)

(defvar foo "initial value")

This is the simplest type of variable. Basic variables don't ever change automatically. Instead, you explicitly update them by calling eww like so: eww update foo="new value".

This is useful if you have values that change very rarely, or may change as a result of some external script you wrote. They may also be useful to have buttons within eww change what is shown within your widget, by setting attributes like onclick to run eww update.

Polling variables (defpoll)

(defvar time-visible false)   ; for :run-while property of below variable
                              ; when this turns true, the polling starts and
                              ; var gets updated with given interval

(defpoll time :interval "1s"
              :initial "initial-value"  ; optional, defaults to poll at startup
              :run-while time-visible   ; optional, defaults to 'true'
  `date +%H:%M:%S`)

A polling variable is a variable which runs a provided shell-script repeatedly, in a given interval.

This may be the most commonly used type of variable. They are useful to access any quickly retrieved value repeatedly, and thus are the perfect choice for showing your time, date, as well as other bits of information such as pending package updates, weather, and battery level.

You can also specify an initial-value. This should prevent eww from waiting for the result of a give command during startup, thus making the startup time faster.

Listening variables (deflisten)

(deflisten foo :initial "whatever"
  `tail -F /tmp/some_file`)

Listening variables might be the most confusing of the bunch. A listening variable runs a script once, and reads its output continously. Whenever the script outputs a new line, the value will be updated to that new line. In the example given above, the value of foo will start out as "whatever", and will change whenever a new line is appended to /tmp/some_file.

These are particularly useful when you want to apply changes instantaneously when an operation happens if you have a script that can monitor some value on its own. Volume, brightness, workspaces that get added/removed at runtime, monitoring currently focused desktop/tag, etc. are the most common usecases of this type of variable. These are particularly efficient and should be preffered if possible.

For example, the command xprop -spy -root _NET_CURRENT_DESKTOP writes the currently focused desktop whenever it changes. Another example usecase is monitoring the currently playing song with playerctl: playerctl --follow metadata --format {{title}}.

Built-in "magic" variables

In addition to defining your own variables, eww provides some values for you to use out of the box. These include values such as your CPU and RAM usage. These mostly contain their data as JSON, which you can then get using the json access syntax. All available magic variables are listed here.

Dynamically generated widgets with literal

In some cases, you want to not only change the text, value, or color of a widget dynamically, but instead want to generate an entire widget structure dynamically. This is necessary if you want to display lists of things (for example notifications) where the amount is not necessarily known, or if you want to change the widget structure in some other, more complex way.

For this, you can make use of one of eww's most powerful features: the literal widget.

(defvar variable_containing_yuck
  "(box (button 'foo') (button 'bar'))")

; Then, inside your widget, use:
(literal :content variable_containing_yuck)

Here, you specify the content of your literal by providing it a string (most likely stored in a variable) which contains a single yuck widget tree. Eww then reads the provided value and renders the resulting widget. Whenever it changes, the widget will be rerendered.

Note that this is not all that efficient. Make sure to only use literal when necessary!

Using window arguments and IDs

In some cases you may want to use the same window configuration for multiple widgets, e.g. for multiple windows. This is where arguments and ids come in.

Window ID

Firstly let us start off with ids. An id can be specified in the open command with --id, by default the id will be set to the name of the window configuration. These ids allow you to spawn multiple of the same windows. So for example you can do:

eww open my_bar --screen 0 --id primary
eww open my_bar --screen 1 --id secondary

When using open-many you can follow the structure below. Again if no id is given, the id will default to the name of the window configuration.

eww open-many my_config:primary my_config:secondary

You may notice with this we didn't set screen, this is set through the --arg system, please see below for more information.

Window Arguments

However this may not be enough and you want to have slight changes for each of these bars, e.g. having a different class for 1080p displays vs 4k or having spawning the window in a different size or location. This is where the arguments come in.

Please note these arguments are CONSTANT and so cannot be update after the window has been opened.

Defining arguments in a window is the exact same as in a widget so you can have:

(defwindow my_bar [arg1 ?arg2]
          :geometry (geometry
                       :x      "0%"
                       :y      "6px"
                       :width  "100%"
                       :height { arg1 == "small" ? "30px" : "40px" }
                       :anchor "top center")
          :stacking   "bg"
          :windowtype "dock"
          :reserve    (struts :distance "50px" :side "top")
    (my_widget :arg2 arg2))

Here we have two arguments, arg1 and arg2 (an optional parameter).

Once we have these parameters, when opening a new window, we must specify them (unless they are required, like arg2), but how? Well, we use the --arg option when running the open command:

eww open my_bar --id primary --arg arg1=some_value --arg arg2=another_value

With the open-many it looks like this:

# Please note that `--arg` option must be given after all the windows names
eww open-many my_bar:primary --arg primary:arg1=some_value --arg primary:arg2=another_value

Using this method you can define screen, anchor, pos, size inside the args for each window and it will act like giving --screen, --anchor etc. in the open command.

So, now you know the basics, I shall introduce you to some of these "special" parameters, which are set slightly differently. However these can all be overridden by the --arg option.

  • id - If id is included in the argument list, it will be set to the id specified by --id or will be set to the name of the config. This can be used when closing the current window through eww commands.
  • screen - If screen is specified it will be set to the value given by --screen, so you can use this in other widgets to access screen specific information.

Further insight into args in open-many

Now due to the system behind processing the open-many --arg option you don't have to specify an id for each argument. If you do not, that argument will be applied across all windows e.g.

eww open-many my_bar:primary my_bar:secondary --arg gui_size="small"

This will mean the config is the same throughout the bars.

Furthermore if you didn't specify an id for the window, you can still set args specifically for that window - following the idea that the id will be set to the window configuration if not given - by just using the name of the window configuration e.g.

eww open-many my_primary_bar --arg my_primary_bar:screen=0

Generating a list of widgets from JSON using for

If you want to display a list of values, you can use the for-Element to fill a container with a list of elements generated from a JSON-array.

(defvar my-json "[1, 2, 3]")

; Then, inside your widget, you can use
(box
  (for entry in my-json
    (button :onclick "notify-send 'click' 'button ${entry}'"
      entry)))

This can be useful in many situations, for example when generating a workspace list from a JSON representation of your workspaces. In many cases, this can be used instead of literal, and should most likely be preferred in those cases.

Splitting up your configuration

As time passes, your configuration might grow larger and larger. Luckily, you can easily split up your configuration into multiple files!

There are two options to achieve this:

Using include

(include "./path/to/your/file.yuck")

A single yuck file may import the contents of any other yuck file. For this, make use of the include directive.

Using a separate eww configuration directory

If you want to separate different widgets even further, you can create a new eww config folder anywhere else. Then, you can tell eww to use that configuration directory by passing every command the --config /path/to/your/config/dir flag. Make sure to actually include this in all your eww calls, including eww kill, eww logs, etc. This launches a separate instance of the eww daemon that has separate logs and state from your main eww configuration.