在 node.js 中一次读取一行文件? [英] Read a file one line at a time in node.js?

问题描述

我正在尝试一次一行读取一个大文件.我发现 Quora 上的一个问题 处理了这个主题，但我缺少一些联系来使整个事情整合在一起.

I am trying to read a large file one line at a time. I found a question on Quora that dealt with the subject but I'm missing some connections to make the whole thing fit together.

 var Lazy=require("lazy");
 new Lazy(process.stdin)
     .lines
     .forEach(
          function(line) { 
              console.log(line.toString()); 
          }
 );
 process.stdin.resume();

我想弄清楚的是如何一次从文件中读取一行，而不是本示例中的 STDIN.

The bit that I'd like to figure out is how I might read one line at a time from a file instead of STDIN as in this sample.

我试过:

 fs.open('./VeryBigFile.csv', 'r', '0666', Process);

 function Process(err, fd) {
    if (err) throw err;
    // DO lazy read 
 }

但它不起作用.我知道在紧要关头我可以退回到使用 PHP 之类的东西，但我想弄清楚这一点.

but it's not working. I know that in a pinch I could fall back to using something like PHP, but I would like to figure this out.

我不认为另一个答案会起作用，因为该文件比我运行它的服务器的内存大得多.

I don't think the other answer would work as the file is much larger than the server I'm running it on has memory for.

推荐答案

从 Node.js v0.12 和 Node.js v4.0.0 开始，有一个稳定的 readline 核心模块.这是从文件中读取行的最简单方法，无需任何外部模块:

Since Node.js v0.12 and as of Node.js v4.0.0, there is a stable readline core module. Here's the easiest way to read lines from a file, without any external modules:

const fs = require('fs');
const readline = require('readline');

async function processLineByLine() {
  const fileStream = fs.createReadStream('input.txt');

  const rl = readline.createInterface({
    input: fileStream,
    crlfDelay: Infinity
  });
  // Note: we use the crlfDelay option to recognize all instances of CR LF
  // ('
') in input.txt as a single line break.

  for await (const line of rl) {
    // Each line in input.txt will be successively available here as `line`.
    console.log(`Line from file: ${line}`);
  }
}

processLineByLine();

或者:

var lineReader = require('readline').createInterface({
  input: require('fs').createReadStream('file.in')
});

lineReader.on('line', function (line) {
  console.log('Line from file:', line);
});

最后一行被正确读取(从 Node v0.12 或更高版本开始)，即使没有最后的 .

The last line is read correctly (as of Node v0.12 or later), even if there is no final .

更新:此示例已添加到 Node 的 API 官方文档.

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