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<main>
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<h1 id="variables"><a class="header" href="#variables">Variables</a></h1>
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<p>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.</p>
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<p>To implement dynamic content in your widgets, you make use of <em>variables</em>.</p>
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<p>All variables are only locally available so you would need to pass it around using function parameters. And whenever the variable changes, the value in the widget will update!</p>
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<h2 id="static-variables"><a class="header" href="#static-variables">Static variables</a></h2>
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<p>In Rhai, all variables are dynamically typed bindings to values. You can define variables using let, pass them as function parameters.</p>
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<p><strong>Basic variables (<code>let</code>)</strong></p>
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<pre><code class="language-rust ignore">let foo = "value";</code></pre>
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<p>This is the simplest type of variable.
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Basic variables don't ever change automatically, if you need a dynamic variable, you can use built in functions like <code>poll()</code> and <code>listen()</code> to register dynamic values which we will talk about in the following section.</p>
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<h2 id="dynamic-variables"><a class="header" href="#dynamic-variables">Dynamic variables</a></h2>
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<p>Just having static variables that wont update is pretty limiting. So, ewwii has two built in functions to register dynamic variables that can change according to the command.</p>
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<p><strong>Polling variables (<code>poll</code>)</strong></p>
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<pre><code class="language-rust ignore">poll("var_name", #{
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// It is recommended to have initial property passed.
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// If not provided, it will default to no value which may cause problems when used.
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// You can pass something like "" if you want no initial value.
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initial: "inital value",
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interval: "2s",
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cmd: "date +%H:%M:%S", // command to execute
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})</code></pre>
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<p>A polling variable is a variable which runs a provided shell-script repeatedly, in a given interval.</p>
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<p>This may be the most commonly used type of variable.
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They are useful to access any quickly retrieved value repeatedly,
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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.
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But it is important to note that these variables are locally available only in enter (a.k.a the root) and you need to pass it to other functions with something like <code>some_fn(foo)</code> when you want to use a polled variable.</p>
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<!-- You can also specify an initial-value. This should prevent ewwii from waiting for the result of a given command during startup, thus
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making the startup time faster. -->
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<p>To externally update a polling variable, <code>ewwii update</code> can be used like with basic variables to assign a value.</p>
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<p><strong>Listening variables (<code>listen</code>)</strong></p>
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<pre><code class="language-rust ignore">listen("foo", #{
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initial: "whatever",
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cmd: "tail -F /tmp/some_file",
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})</code></pre>
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<p>Listening variables might be the most confusing of the bunch.
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A listening variable runs a script once, and reads its output continously.
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Whenever the script outputs a new line, the value will be updated to that new line.
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In the example given above, the value of <code>foo</code> will start out as <code>"whatever"</code>, and will change whenever a new line is appended to <code>/tmp/some_file</code>.</p>
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<p>These are particularly useful when you want to apply changes instantaneously when an operation happens if you have a script
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that can monitor some value on its own. Volume, brightness, workspaces that get added/removed at runtime,
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monitoring currently focused desktop/tag, etc. are the most common usecases of this type of variable.
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These are particularly efficient and should be preffered if possible.</p>
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<p>For example, the command <code>xprop -spy -root _NET_CURRENT_DESKTOP</code> writes the currently focused desktop whenever it changes.
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Another example usecase is monitoring the currently playing song with playerctl: <code>playerctl --follow metadata --format {{title}}</code>.</p>
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<!--
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**Built-in "magic" variables**
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In addition to defining your own variables, ewwii provides some values for you to use out of the box.
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These include values such as your CPU and RAM usage.
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These mostly contain their data as JSON, which you can then get using the [json access syntax](expression_language.md).
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All available magic variables are listed [here](magic-vars.md). -->
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<h2 id="passing-variables"><a class="header" href="#passing-variables">Passing variables</a></h2>
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<p>As we discussed earlier, all variables are only available locally. So, you would need to pass it around from the current scope.</p>
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<p>Here is an example of how it is done:</p>
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<pre><code class="language-rust ignore">let foo = "example";
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poll("time", #{
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initial: "inital value",
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interval: "2s",
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cmd: "date +%H:%M:%S",
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})
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// Here we have 2 variables named "time" (registered dynamically by poll) and foo (a static variable)
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// here is an example of something that wont
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fn wont_work() {
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return box(#{}, [ label(#{ text: time }), label(#{ text: foo }) ]);
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}</code></pre>
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<h2 id="dyn_id"><a class="header" href="#dyn_id">dyn_id</a></h2>
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<p><code>dyn_id</code>'s are one of the most important properties of all. It is the property that decides if a widget should get updated dynamic or not.</p>
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<p><code>dyn_id</code> property is used to assign an id to a widget which the system will track to update if there is a change in property under the same id.</p>
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<p><strong>Example usage:</strong></p>
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<pre><code class="language-rust ignore">fn foo(foo_var) {
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return box(#{}, [
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label(#{ text: foo_var, dyn_id: "foo_var_user" }); // dyn_id used to make label dynamic
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]);
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}
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enter([
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defpoll("foo", #{
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cmd: "echo baz",
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initial: "",
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interval: "1s"
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}),
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defwindow("bar", #{
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// .. properties omitted
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}, bar(foo)),
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])</code></pre>
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<p>Here, when the variable foo changes, the text of label changes as well. If there is no <code>dyn_id</code> defined, then ewwii will ingore that change. But if it is defined with a unique value, then it will find the widget that is defined with the id that matches dyn_id and then update its text property which will result in a change in the UI.</p>
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