//异步
fs.readFile('test.txt', 'utf-8' (err, data) => {
  if (err) {
    throw err;
  }
  console.log(data);
});

//同步
let data = fs.readFileSync('test.txt');
console.log(data);

fs.writeFile('test2.txt', 'this is text', { 'flag': 'w' }, err => {
  if (err) {
    throw err;
  }
  console.log('saved');
});

fs.mkdir('dir', (err) => {
  if (err) {
    throw err;
  }
  console.log('make dir success');
});

fs.readdir('dir',(err, files) => {
  if (err) {
    throw err;
  }
  console.log(files);
}); 

fs.stat('test.txt', (err, stats)=> {
  console.log(stats.isFile());     //true
})

let stream = fs.createReadStream('test.txt');

let stream = fs.createWriteStreamr('test_copy.txt');

let fs = require('fs'),
  src = 'src',
  dist = 'dist',
  args = process.argv.slice(2),
  filename = 'image',
  index = 0;

//show help
if (args.length === 0 || args[0].match('--help')) {
  console.log('--help\n \t-src 文件源\n \t-dist 文件目标\n \t-n 文件名\n \t-i 文件名索引\n');
  return false;
}

args.forEach((item, i) => {
  if (item.match('-src')) {
    src = args[i + 1];
  } else if (item.match('-dist')) {
    dist = args[i + 1];
  } else if (item.match('-n')) {
    filename = args[i + 1];
  } else if (item.match('-i')) {
    index = args[i + 1];
  }
});

fs.readdir(src, (err, files) => {
  if (err) {
    console.log(err);
  } else {
    fs.exists(dist, exist => {
      if (exist) {
        copyFile(files, src, dist, filename, index);
      } else {
        fs.mkdir(dist, () => {
          copyFile(files, src, dist, filename, index);
        })
      }
    });
  }
});

function copyFile(files, src, dist, filename, index) {
  files.forEach(n => {
    let readStream,
      writeStream,
      arr = n.split('.'),
      oldPath = src + '/' + n,
      newPath = dist + '/' + filename + index + '.' + arr[arr.length - 1];
    fs.stat(oldPath, (err, stats) => {
      if (err) {
        console.log(err);
      } else if (stats.isFile()) {
        readStream = fs.createReadStream(oldPath);
        writeStream = fs.createWriteStream(newPath);
        readStream.pipe(writeStream);
      }
    });
    index++;
  })
}