feat: add support for polling a variable once at startup

CHANGELOG.md

@@ -42,6 +42,7 @@ All notable changes to eww will be listed here, starting at changes since versio
 - Add `value-pos` to scale widget (By: ipsvn)
 - Add `floor` and `ceil` function calls to simplexpr (By: wsbankenstein)
 - Add `formatbytes` function calls to simplexpr (By: topongo)
+- Add support for polling a variable only once (By: aspen-otr)
 
 ## [0.6.0] (21.04.2024)
 

crates/eww/src/script_var_handler.rs

@@ -168,6 +168,10 @@ impl PollVarHandler {
                 crate::error_handling_ctx::print_error(err);
             }
 
+            if var.interval.is_zero() {
+                return;
+            }
+
             crate::loop_select_exiting! {
                 _ = cancellation_token.cancelled() => break,
                 _ = tokio::time::sleep(var.interval) => {

docs/src/configuration.md

@@ -209,6 +209,8 @@ and thus are the perfect choice for showing your time, date, as well as other bi
 You can also specify an initial-value. This should prevent eww from waiting for the result of a given command during startup, thus
 making the startup time faster.
 
+If the specified interval is `0` or `"0s"`, then the polling variable will only poll its script automatically once, when initialized.
+
 To externally update a polling variable, `eww update` can be used like with basic variables to assign a value.
 You can also call `eww poll` to poll the variable outside of its usual interval, or even while it isn't running at all.