Node.js读写文件行 [英] Node.js read and write file lines

问题描述

我尝试逐行读取文件，然后使用Node.js将其输出到另一个文件。

I tried to read a file line by line, and output it to another file, using Node.js.

我的问题是有时会混乱的行序列由于Node.js的异步性质。

My problem is the sequence of lines sometimes messed up due to async nature of Node.js.

例如我的输入文件如下：
line 1
line 2
line 3

eg my input file is like: line 1 line 2 line 3

但输出文件可能如下：
line 1
line 3
line 2

but output file could be like: line 1 line 3 line 2

以下是我的代码。

var fs  = require("fs");
var index = 1;

fs.readFileSync('./input.txt').toString().split('\n').forEach(
function (line) { 
    console.log(line);
        fs.open("./output.txt", 'a', 0666, function(err, fd) {
            fs.writeSync(fd, line.toString() + "\n", null, undefined, function(err, written) {
            })});
    }
);

任何想法都会受到赞赏，谢谢。

Any thoughts would be appreciated, thanks.

推荐答案

如果您正在编写同步代码，请仅使用同步函数：

If you're writing a synchronous code, use only the synchronous functions:

var fs  = require("fs");

fs.readFileSync('./input.txt').toString().split('\n').forEach(function (line) { 
    console.log(line);
    fs.appendFileSync("./output.txt", line.toString() + "\n");
});

对于异步方法，您可以编写类似

For asynchronous approach you could write something like

var fs = require('fs'),
    async = require('async'),
    carrier = require('carrier');

async.parallel({
    input: fs.openFile.bind(null, './input.txt', 'r'),
    output: fs.openFile.bind(null, './output.txt', 'a')
}, function (err, result) {
    if (err) {
        console.log("An error occured: " + err);
        return;
    }

    carrier.carry(result.input)
        .on('line', result.output.write)
        .on('end', function () {
            result.output.end();
            console.log("Done");
        });
});

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