added yamltool sort

cmd/yamltool/support.go

@@ -0,0 +1,23 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+)
+
+func read(file string) ([]byte, error) {
+
+	if file == "-" {
+		data, err := io.ReadAll(os.Stdin)
+		if err != nil {
+			return nil, fmt.Errorf("Error reading from stdin")
+		}
+		return data, nil
+	}
+	data, err := os.ReadFile(file)
+	if err != nil {
+		return nil, fmt.Errorf("Error reading from '%s'", file)
+	}
+	return data, nil
+}