test variables

action.yml

@@ -1,6 +1,10 @@
 name: 'Hello World'
 description: 'Greet someone'
 inputs:
+  message_id:
+    description: "Message ID"
+    required: false
+    default: ${{ env.MESSAGE_ID }}
   who-to-greet:  # id of input
     description: 'Who to greet'
     required: true
@@ -13,10 +17,15 @@ runs:
   using: "composite"
   steps:
     - name: Set Greeting
-      run: echo "Hello $INPUT_WHO_TO_GREET."
+      run: |
+        echo "Hello $INPUT_WHO_TO_GREET."
+        echo MESSAGE=$MESSAGE
+        echo inputs.message_id==${{ inputs.message_id }}
+        echo env.MESSAGE_ID=${{ env.MESSAGE_ID }}
       shell: bash
       env:
         INPUT_WHO_TO_GREET: ${{ inputs.who-to-greet }}
+        MESSAGE: ${{ inputs.message_id }}
 
     - name: Random Number Generator
       id: random-number-generator