static void logOutputPlain() {
  set(getJavaX(), "customSystemOut", new Appendable() {
    File logFile = getProgramFile("output.txt");
    
    // only using this one
    public Appendable append(CharSequence cs) {
      appendToTextFile(logFile, cs.toString());
      return this;
    }

    public Appendable append(char c) { return this; }
    public Appendable append(CharSequence s, int start, int end) { return this; }
  });
}

Began life as a copy of #1002226