Add format function

app/cmd/common.go

+package cmd
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"gopkg.in/yaml.v2"
+)
+
+type OutputOption struct {
+	Format string
+}
+
+const (
+	JsonOutputFormat string = "json"
+	YAMLOutputFormat string = "yaml"
+)
+
+func Format(obj interface{}, format string) (data []byte, err error) {
+	if format == JsonOutputFormat {
+		return json.MarshalIndent(obj, "", "  ")
+	} else if format == YAMLOutputFormat {
+		return yaml.Marshal(obj)
+	}
+
+	return nil, fmt.Errorf("not support format %s", format)
+}