我试图读取一个大文件一行在一次。我在Quora上找到了一个关于这个主题的问题,但我错过了一些联系,把整个事情联系在一起。
var Lazy=require("lazy");
new Lazy(process.stdin)
.lines
.forEach(
function(line) {
console.log(line.toString());
}
);
process.stdin.resume();
我想要弄清楚的是如何一次从文件中读取一行,而不是像本例中那样读取STDIN。
我试着:
fs.open('./VeryBigFile.csv', 'r', '0666', Process);
function Process(err, fd) {
if (err) throw err;
// DO lazy read
}
但这并不奏效。我知道在必要时我可以使用PHP之类的东西,但我想弄清楚这个问题。
我不认为其他答案会起作用,因为文件比我运行它的服务器的内存大得多。
在Node.js v18.11.0中添加了一个逐行读取文件的新函数
filehandle.readLines([选项])
这就是如何将此功能用于想要读取的文本文件
import { open } from 'node:fs/promises';
myFileReader();
async function myFileReader() {
const file = await open('./TextFileName.txt');
for await (const line of file.readLines()) {
console.log(line)
}
}
为了了解更多read Node.js文档,这里有文件系统readlines()的链接:
https://nodejs.org/api/fs.html#filehandlereadlinesoptions
var fs = require('fs');
function readfile(name,online,onend,encoding) {
var bufsize = 1024;
var buffer = new Buffer(bufsize);
var bufread = 0;
var fd = fs.openSync(name,'r');
var position = 0;
var eof = false;
var data = "";
var lines = 0;
encoding = encoding || "utf8";
function readbuf() {
bufread = fs.readSync(fd,buffer,0,bufsize,position);
position += bufread;
eof = bufread ? false : true;
data += buffer.toString(encoding,0,bufread);
}
function getLine() {
var nl = data.indexOf("\r"), hasnl = nl !== -1;
if (!hasnl && eof) return fs.closeSync(fd), online(data,++lines), onend(lines);
if (!hasnl && !eof) readbuf(), nl = data.indexOf("\r"), hasnl = nl !== -1;
if (!hasnl) return process.nextTick(getLine);
var line = data.substr(0,nl);
data = data.substr(nl+1);
if (data[0] === "\n") data = data.substr(1);
online(line,++lines);
process.nextTick(getLine);
}
getLine();
}
我也有同样的问题,想出了上面的解决方案
看起来类似于其他,但是异步的,可以读取大文件非常快
希望这能有所帮助
我对缺乏全面的解决方案感到沮丧,所以我把自己的尝试(git / npm)放在一起。复制粘贴功能列表:
Interactive line processing (callback-based, no loading the entire file into RAM)
Optionally, return all lines in an array (detailed or raw mode)
Interactively interrupt streaming, or perform map/filter like processing
Detect any newline convention (PC/Mac/Linux)
Correct eof / last line treatment
Correct handling of multi-byte UTF-8 characters
Retrieve byte offset and byte length information on per-line basis
Random access, using line-based or byte-based offsets
Automatically map line-offset information, to speed up random access
Zero dependencies
Tests
国家卫生研究院?你决定:-)
function createLineReader(fileName){
var EM = require("events").EventEmitter
var ev = new EM()
var stream = require("fs").createReadStream(fileName)
var remainder = null;
stream.on("data",function(data){
if(remainder != null){//append newly received data chunk
var tmp = new Buffer(remainder.length+data.length)
remainder.copy(tmp)
data.copy(tmp,remainder.length)
data = tmp;
}
var start = 0;
for(var i=0; i<data.length; i++){
if(data[i] == 10){ //\n new line
var line = data.slice(start,i)
ev.emit("line", line)
start = i+1;
}
}
if(start<data.length){
remainder = data.slice(start);
}else{
remainder = null;
}
})
stream.on("end",function(){
if(null!=remainder) ev.emit("line",remainder)
})
return ev
}
//---------main---------------
fileName = process.argv[2]
lineReader = createLineReader(fileName)
lineReader.on("line",function(line){
console.log(line.toString())
//console.log("++++++++++++++++++++")
})
在Node.js v18.11.0中添加了一个逐行读取文件的新函数
filehandle.readLines([选项])
这就是如何将此功能用于想要读取的文本文件
import { open } from 'node:fs/promises';
myFileReader();
async function myFileReader() {
const file = await open('./TextFileName.txt');
for await (const line of file.readLines()) {
console.log(line)
}
}
为了了解更多read Node.js文档,这里有文件系统readlines()的链接:
https://nodejs.org/api/fs.html#filehandlereadlinesoptions