read body from file if specified so

.github/workflows/test.yml

@@ -8,6 +8,11 @@ on:
 jobs:
   main:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        body:
+          - README.md
+          - Test of action completed successfully!
     steps:
       - name: Checkout
         uses: actions/checkout@v1
@@ -19,6 +24,6 @@ jobs:
           username: ${{secrets.USERNAME}}
           password: ${{secrets.PASSWORD}}
           subject: ${{github.repository}}
-          body: Test of action completed successfully!
+          body: ${{matrix.body}}
           to: ${{secrets.USERNAME}}
           from: github-actions

action.yml

@@ -21,7 +21,7 @@ inputs:
     description: Subject of mail message
     required: true
   body:
-    description: Body of mail message
+    description: Body of mail message (might be a filename to read from)
     required: true
   to:
     description: Recipients mail addresses (separated with comma)

main.rb

@@ -13,6 +13,9 @@
 to = ENV['INPUT_TO']
 from = ENV['INPUT_FROM']
 
+# Body
+body = File.exist?(body) ? File.read(body) : body
+
 # Message
 message = <<~END_OF_MESSAGE
   Subject: #{subject}