RHDEVDOCS 6177 explain optional workspaces

modules/op-about-workspace.adoc

@@ -107,3 +107,31 @@ spec:
 <1> Specifies the list of pipeline workspaces for which volume binding will be provided in the pipeline run.
 <2> The name of the workspace in the pipeline for which the volume is being provided.
 <3> Specifies a volume claim template that creates a persistent volume claim to define the storage volume for the workspace.
+
+In the definition of a task, you can use the `$(workspaces.source.path)` variable to refer to the path where the workspace is mounted.
+
+Normally, if you define a workspace in a pipeline or task and then don't provide the workspace in the pipeline run or task run, the run fails. However, you can mark a workspace as _optional_ by adding an `optional: true` field to the definition of the workspace. In this case, you do not have to provide the workspace in the pipeline run or task run. If the workspaces is not provided, the `$(workspaces.source.path)` variable has an empty value.
+
+The following code snippet defines a task with an optional workspace.
+
+[source,yaml]
+----
+apiVersion: tekton.dev/v1
+kind: Task
+metadata:
+  name: demo-optional-workspace
+spec:
+  workspaces:
+  - name: output
+    optional: true
+  steps:
+    - name: echo
+      image: registry.access.redhat.com/ubi9/ubi-micro
+      env:
+      - name: OUTPUT
+      value: $(workspaces.output.path)
+  script: |
+    #!/usr/bin/env bash
+    echo "hello world"
+    if [[ "" != $OUTPUT ]]; then echo "hello world" >> $OUTPUT/hello ; fi
+----