node.js如何将字符串插入文件的开头但不替换原始文本？

The code below inserted somestring to file but also will replace the text inside the file. how can fix this?

下面的代码将somestring插入到文件中,但也将替换文件中的文本。怎么解决这个问题?

fd = fs.openSync('file', 'r+')
buf = new Buffer('somestring')
fs.writeSync(fd, buf, 0, buf.length, 0)
fs.close(fd)

2 个解决方案

#1

Open the file in append mode using the a+ flag

使用a +标志以追加模式打开文件

var fd = fs.openSync('file', 'a+');

Or use a positional write. To be able to append to end of file, use fs.appendFile:

或者使用位置写入。要能够追加到文件末尾,请使用fs.appendFile:

fs.appendFile(fd, buf, err => {
  //
});

Write to the beginning of a file:

写到文件的开头:

fs.write(fd, buf, 0, buf.length, 0);

EDIT:

I guess there isn't a single method call for that. But you can copy the contents of the file, write new data, and append the copied data.

我想没有一个方法调用。但您可以复制文件的内容,写入新数据并附加复制的数据。

var data = fs.readFileSync(file); //read existing contents into data
var fd = fs.openSync(file, 'w+');
var buffer = new Buffer('New text');

fs.writeSync(fd, buffer, 0, buffer.length, 0); //write new data
fs.writeSync(fd, data, 0, data.length, buffer.length); //append old data
// or fs.appendFile(fd, data);
fs.close(fd);

Please note that you must use the asynchronous versions of these methods if these operations aren't performed just once during initialization, as they'll block the event loop.

请注意,如果这些操作在初始化期间不执行一次,则必须使用这些方法的异步版本,因为它们将阻止事件循环。

#2

With small files you can do it like this:

使用小文件,您可以这样做:

let logPath = path.join(appPath, 'deploy.log');
let logRows = fs.readFileSync(logPath).toString().split('\n');

logRows.unshift('Your string here');
fs.writeFileSync(logPath, logRows.join('\n'));

Hope it would be useful for someone!

希望它对某人有用!

#1