读取CSV文件的最后一行并提取一个值

Question

Node.js的新手,并尝试从CSV文件的最后一行中提取值.这是CSV:

Unit ID,Date,Time,Audio File
Log File Created,3/6/2013,11:18:25 AM,file:\\\C:\Users\Ben\Documents\1_03-06-2013_1114-50.mp3
1,3/6/2013,11:20:24 AM,file:\\\C:\AlertLog\1_03-06-2013_1120-24.mp3
1,3/6/2013,11:20:39 AM,file:\\\C:\AlertLog\1_03-06-2013_1120-24.mp3

我试图抓住的部分是file:\\\C:\AlertLog\1_03-06-2013_1120-24.mp3- 最好摆脱这file:\\\部分.

很抱歉,我没有任何代码可以显示,只有几个小时的Node.js经验,似乎无法找到任何关于如何完成这样的事情的文档.任何帮助,将不胜感激.谢谢!

Answer 1

我通过向后读取文件直到读完最后一行来完成它:

var fs = require('fs');
var path = require('path');
var fileName = path.join(__dirname, 'test.txt');
var readLastLine = function(name, callback) {
    fs.stat(name, function(err, stat) {
        fs.open(name, 'r', function(err, fd) {
            if(err) throw err;
            var i = 0;
            var line = '';
            var readPrevious = function(buf) {
                fs.read(fd, buf, 0, buf.length, stat.size-buf.length-i, function(err, bytesRead, buffer) {
                    if(err) throw err;
                    line = String.fromCharCode(buffer[0]) + line;
                    if (buffer[0] === 0x0a) { //0x0a == '\n'
                        callback(line);
                    } else {
                        i++;
                        readPrevious(new Buffer(1));
                    }
                });
            }
            readPrevious(new Buffer(1));
        });
    });
}
readLastLine(fileName, function(line) {
    console.log(line);
});

Answer 2

常规文件

像常规文件一样读取文件,将文件内容拆分为行,取最后一行,用逗号分割并取最后一部分.

var fs = require('fs'); // file system module

fs.readFile('/path/to/file.csv', 'utf-8', function(err, data) {
    if (err) throw err;

    var lines = data.trim().split('\n');
    var lastLine = lines.slice(-1)[0];

    var fields = lastLine.split(',');
    var audioFile = fields.slice(-1)[0].replace('file:\\\\', '');

    console.log(audioFile);
});

文件系统模块文档

CSV解析器

您还可以使用node-csv-parser模块.

var fs = require('fs');
var csv = require('csv');

csv()
 .from.stream(fs.createReadStream('/path/to/file.csv'))
 .to.array(function(data, count) {
    var lastLine = data.slice(-1)[0];
    var audioFile = lastLine.slice(-1)[0].replace('file:\\\\', '');
    console.log(audioFile);
  });