node.jsでファイルを一行づつ読み込む

filereadline.js

/**
 *  file read line
 */
"use strict";
var fs = require("fs");

/**
 *  node.js 0.8 or 0.10 setting
 */
var _setImmediate = (function(){
    return (global.setImmediate ? setImmediate :
            (process.nextTick ?   process.nextTick :
                                  function(cb){ setTimeout(cb, 0); }
    ));
})();

// execCallback = function(line){}
// resultCallback = function(err){}
var fileReadLine = module.exports = function( filepath, execCallback, resultCallback ){
    fs.open(filepath, 'r', function( err, fd ){
        if( err ){
            resultCallback(err);
            return;
        }
        var buffSize = 4096;
        var tmp = "";
        var update = function(pos){
            _setImmediate(function(){
                fs.read(fd, buffSize, pos, "utf-8", function( err, readBuff, readBytes ){
                    if( err ){
                        fs.close(fd, function(){
                            resultCallback(err);
                        });                                                                                                                                                                                                                  
                        return;
                    }
                    if( readBytes === 0 ){
                        fs.close(fd, function(){
                            resultCallback(null);
                        });                                                                                                                                                                                                                  
                    }else{
                        tmp += readBuff;
                        var lines = tmp.split("\n");
                        for(var i = 0; i<lines.length - 1; ++i){
                            execCallback(lines[i]);
                        }
                        if(lines.length > 1){
                            tmp = lines[lines.length - 1];
                        }
                        update(pos + readBytes);
                    }
                });
            });
        };
        update(0);
    });
};

gistfile1.txt

var fs = require('fs'),
    readline = require('readline');

var filepath = "textdata.log";

var rs = fs.ReadStream(filepath);
var rl = readline.createInterface({'input': rs, 'output': {}});

var i = 0;
rl.on('line', function (line) {
    console.log(i++ + ': ' + line.trim());
});
rl.on('close', function(){
    console.log("end");
});
rl.resume();

http://superbrothers.hatenablog.com/entry/2012/12/11/003310
スマートなやり方があった