node fs 模块read的使用

var fs = require('fs');
var path = require('path');
var loadPath;
var savePath;
process.argv.forEach((val, index) => {
  console.log(`${index}: ${val}`);
  if (index === 2) {
    loadPath = val;
  }
  if (index === 3) {
    savePath = val;
  }
});
if (!loadPath) {
  console.log('请输入要打开的文件地址');
  return;
}
var lineStr = '';
var selectList = [];
var selectKey = '文章';
var fsRead = function (fd, buffer) {
  //每一个汉字utf8编码是3个字节，英文是1个字节
  fs.read(fd, buffer, 0, 255, null, function (err, bytesRead, buffer) {
    if(err) {
      throw err;
    } else {
      let str = '';
      if (bytesRead === 255) {
        str = buffer.toString();
        console.log(buffer.toString());
      } else {
        str = buffer.slice(0, bytesRead).toString();
        console.log(bytesRead);
        console.log(buffer.slice(0, bytesRead).toString());
      }
      if (lineStr) {
        str += lineStr;
      }
      let strList;
      let isNotLine = false;
      if (!str.includes('\n')) {
        // 没有换行符号
        lineStr = str;
        isNotLine = true;
      } else if (str[str.length - 1] === '\n') {
        lineStr = '';
        // 最后一个值是换行符号
      } else {
        // 被换行父分割
        strList = str.split('\n');
        lineStr = strList[strList.length - 1]; 
      }
      let len = 0;
      if (strList) { // 被换行符分割过了。 
        len = strList.length - 1;
      } else if (!isNotLine) { // 刚好分割完
        strList = str.split('\n');
        len = strList.length;
      }
      if (strList) {
        for (let i = 0; i < strList.length - 1; i +=1) {
          const item = strList[i]
          if (item.includes(selectKey)) {
            selectList.push(item);
          }
        }
      }
      if (bytesRead === 255) {
        fsRead(fd, buffer);
      } else {
        console.log(selectList.join('\n'));
      }
    }
  });
}
if (loadPath[0] !== '/') {
  loadPath = path.join(__dirname, loadPath);
}
fs.open(loadPath, 'r', function (err, fd) {
  if(err) {
    console.error(err);
    return;
  } else {
    var buffer = Buffer.alloc(255);
    fsRead(fd, buffer);
  }
});
console.log('>>>>>>>>>>>>>>')
fs.readFile(path.join(__dirname, loadPath), (err, data) => {
  if (err) throw err;
  // console.log(data.toString());
  var text = data.toString();
  text.replace(/\/\/(.)*\n/g, '');
  if (savePath) {
    fs.writeFile(path.join(__dirname, savePath), data, (err) => {
      if (err) throw err;
      console.log('文件已被保存');
    });
  }
});

function getDirPath(dirStr) {
  const paths = [];
  const dirs = dirStr.split('/');
  const isTop = dirStr.split('')[0] === '/';
  dirs.forEach((item, index) => {
    if (!item) {
      return
    }
    if (index === dirs.length - 1 && item.includes('.')) {
      return
    }
    if (paths.length === 0) {
      if (isTop) {
        paths.push(`/${item}`)
      } else {
        paths.push(`${item}`)
      }
      return
    }
    paths.push(`${paths[paths.length - 1]}/${item}`)
  })
  return paths
}