doc: Add example how to parse pebble in variables (#591)

content/docs/05.developer-guide/03.variables/01.index.md

@@ -158,7 +158,40 @@ The `Return` task has an output attribute `value` which is used by the `log-both
 In the `log-both-variables` task, you can see two ways to access task outputs: the dot notation (`outputs.firstExample`) and the subscript notation (`outputs['second-example']`). The subscript notation must be used when a variable contains a special character, such as `-` that is a Pebble reserved character.
 ::
 
-## Pebble templating
-Pebble templating offers various ways to process variables, see:
+
+## Pebble templating: example
+
+The example below will parse the Pebble expressions within the `variables` based on the `inputs` and `trigger` values. Both variables use the [Null-Coalescing Operator](02.basic-usage.md#null-coalescing-operator) to use the first non-null value.
+
+Here, the first variable `trigger_or_yesterday` will evaluate to a `trigger.date` if the flow runs on schedule. Otherwise, it will evaluate to the yesterday's date by using the `execution.startDate` minus one day.
+
+The second variable `input_or_yesterday` will evaluate to the `mydate` input if it's provided. Otherwise, it will evaluate to the yesterday's date — again, using the `execution.startDate` and subtracting one day with the help of the `dateAdd` function.
+
+```yaml
+id: vars_example
+namespace: dev
+
+inputs:
+  - name: mydate
+    type: DATETIME
+    required: false
+
+variables:
+  trigger_or_yesterday: "{{ trigger.date ?? (execution.startDate | dateAdd(-1, 'DAYS')) }}"
+  input_or_yesterday: "{{ inputs.mydate ?? (execution.startDate | dateAdd(-1, 'DAYS')) }}"
+
+tasks:
+  - id: yesterday
+    type: io.kestra.core.tasks.log.Log
+    message: "{{ vars.trigger_or_yesterday }}"
+
+  - id: input_or_yesterday
+    type: io.kestra.core.tasks.log.Log
+    message: "{{ vars.input_or_yesterday }}"
+```
+
+
+## Pebble templating: deep dive
+Pebble templating offers a myriad of ways to process variables. For a deep dive, check the following section:
 
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