Default targets to stdin and abstract file handling

file.go

@@ -0,0 +1,26 @@
+package main
+
+import (
+	"os"
+)
+
+func file(filename string, create bool) (*os.File, error) {
+	switch filename {
+	case "stdin":
+		return os.Stdin, nil
+	case "stdout":
+		return os.Stdout, nil
+	default:
+		var file *os.File
+		var err error
+		if create {
+			file, err = os.Create(filename)
+		} else {
+			file, err = os.Open(filename)
+		}
+		if err != nil {
+			return nil, err
+		}
+		return file, nil
+	}
+}