fs.renameSync(oldPath, newPath)

var fs = require('fs');
fs.renameSync('125.txt','126.txt');

fs.renameSync = function(oldPath, newPath) {
  nullCheck(oldPath);
  nullCheck(newPath);
  return binding.rename(pathModule._makeLong(oldPath),
                        pathModule._makeLong(newPath));
};