Stability: 3 – Stable

File System 的每个API都有异步方式和同步方式，两种方式的区别在于异步方式具有一个回调函数，并且这个回调函数的第一个参数为 err，如果操作成功，这个参数为 null 或 undefined

rename : 改名

fs.rename(oldPath, newPath, callback)

//Asynchronous rename
fs.rename('/path/demo.txt', '/path/demo1.txt', function (err) {
  if (err) {
    throw err;
  }
  console.log('renamed complete');
});

fs.renameSync(oldPath, newPath)

//Synchronous rename
fs.renameSync('path/demo.txt', '/path/demo1.txt');

ftruncate : 截断文件(fd)

fs.ftruncate(fd, len, callback)

//Asynchronous ftruncate
fs.open('/path/demo1.txt', 'a', function (err, fd) {
  if (err) {
    throw err;
  }
  fs.ftruncate(fd, 50, function (err) {
    if (err) {
      throw err;
    }
    console.log(fd);
    fs.close(fd, function () {
      console.log('Done');
    });
  });
});

fs.ftruncateSync(fd, len)

//Synchronous ftruncate
var fd = fs.openSync('/path/demo1.txt', 'a');
fs.ftruncateSync(fd, 50);
console.log(fd);
fs.closeSync(fd);
console.log('Done');

truncate : 截断文件(path)

fs.truncate(path, len, callback)

//Asynchronous truncate
fs.open('/path/demo1.txt', 'r+', function (err, fd) {
  if (err) {
    throw err;
  }
  fs.truncate('/path/demo1.txt', 10, function (err) {
    if (err) {
      throw err;
    }
    console.log(fd);
    fs.close(fd, function () {
      console.log('Done');
    });
  });
});

fs.truncateSync(path, len)

//Synchronous truncate
var fd = fs.openSync('/path/demo1.txt', 'r+');
fs.truncateSync('/path/demo1.txt', 5);
console.log(fd);
fs.close(fd);
console.log('Done');