Use tar to support multiple wildcards in source:

README.md

@@ -24,7 +24,7 @@
 ```yaml
 ---
 kind: pipeline
-name: deploy to swarm
+name: deploy to docker container
 steps:
   - name: docker cp deploy
     image: 3wordchant/docker-cp-deploy:latest

plugin.sh

@@ -38,7 +38,7 @@ run_docker_cp() {
     return 1
   fi
   echo docker -H "$REMOTE_DOCKER_HOST" cp "$PLUGIN_SOURCE" "$CONTAINER:$PLUGIN_DEST"
-  docker -H "$REMOTE_DOCKER_HOST" cp "$PLUGIN_SOURCE" "$CONTAINER:$PLUGIN_DEST"
+  tar cf - "$PLUGIN_SOURCE" | docker -H "$REMOTE_DOCKER_HOST" cp - "$CONTAINER:$PLUGIN_DEST"
   echo "--- end deploy ---"
 }