Nodejs 进阶：readline 实现日志分析 + 简易命令行工具-白红宇

本文摘录自《Nodejs学习笔记》，更多章节及更新，请访问。欢迎加群交流，群号。

模块概览

readline是个非常实用的模块。如名字所示，主要用来实现逐行读取，比如读取用户输入，或者读取文件内容。常见使用场景有下面几种，本文会逐一举例说明。本文相关代码可在笔者上找到。

文件逐行读取：比如说进行日志分析。

自动完成：比如输入npm，自动提示"help init install"。

命令行工具：比如npm init这种问答式的脚手架工具。

基础例子

先看个简单的例子，要求用户输入一个单词，然后自动转成大写

const readline = require('readline');const rl = readline.createInterface({    input: process.stdin,    output: process.stdout});rl.question('Please input a word: ', function(answer){    console.log('You have entered {%s}', answer.toUpperCase());    rl.close();});复制代码

运行如下：

➜  toUpperCase git:(master) ✗ node app.js Please input a word: helloYou have entered {HELLO}复制代码

例子：文件逐行读取：日志分析

比如我们有如下日志文件access.log，我们想要提取“访问时间+访问地址”，借助readline可以很方便的完成日志分析的工作。

[2016-12-09 13:56:48.407] [INFO] access - ::ffff:127.0.0.1 - - "GET /oc/v/account/user.html HTTP/1.1" 200 213125 "http://www.example.com/oc/v/account/login.html" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.98 Safari/537.36"[2016-12-09 14:00:10.618] [INFO] access - ::ffff:127.0.0.1 - - "GET /oc/v/contract/underlying.html HTTP/1.1" 200 216376 "http://www.example.com/oc/v/account/user.html" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.98 Safari/537.36"[2016-12-09 14:00:34.200] [INFO] access - ::ffff:127.0.0.1 - - "GET /oc/v/contract/underlying.html HTTP/1.1" 200 216376 "http://www.example.com/oc/v/account/user.html" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.98 Safari/537.36"复制代码

代码如下：

const readline = require('readline');const fs = require('fs');const rl = readline.createInterface({    input: fs.createReadStream('./access.log')});rl.on('line', (line) => {    const arr = line.split(' ');     console.log('访问时间：%s %s，访问地址：%s', arr[0], arr[1], arr[13]);});复制代码

运行结果如下：

➜  lineByLineFromFile git:(master) ✗ node app.js访问时间：[2016-12-09 13:56:48.407]，访问地址："http://www.example.com/oc/v/account/login.html"访问时间：[2016-12-09 14:00:10.618]，访问地址："http://www.example.com/oc/v/account/user.html"访问时间：[2016-12-09 14:00:34.200]，访问地址："http://www.example.com/oc/v/account/user.html"复制代码

例子：自动完成：代码提示

这里我们实现一个简单的自动完成功能，当用户输入npm时，按tab键，自动提示用户可选的子命令，如help、init、install。

输入np，按下tab：自动补全为npm

输入npm in，按下tab：自动提示可选子命令 init、install

输入npm inst，按下tab：自动补全为 npm install

const readline = require('readline');const fs = require('fs');function completer(line) {    const command = 'npm';    const subCommands = ['help', 'init', 'install'];    // 输入为空，或者为npm的一部分，则tab补全为npm    if(line.length < command.length){        return [command.indexOf(line) === 0 ? [command] : [], line];    }    // 输入 npm，tab提示 help init install    // 输入 npm in，tab提示 init install    let hits = subCommands.filter(function(subCommand){         const lineTrippedCommand = line.replace(command, '').trim();        return lineTrippedCommand && subCommand.indexOf( lineTrippedCommand ) === 0;    })    if(hits.length === 1){        hits = hits.map(function(hit){            return [command, hit].join(' ');        });    }    return [hits.length ? hits : subCommands, line];}const rl = readline.createInterface({  input: process.stdin,  output: process.stdout,  completer: completer});rl.prompt();复制代码

代码运行效果如下，当输入npm in，按下tab键，则会自动提示可选子命令init、install。

➜  autoComplete git:(master) ✗ node app.js> npm ininit     install复制代码

例子：命令行工具：npmt init

下面借助readline实现一个迷你版的npm init功能，运行脚本时，会依次要求用户输入name、version、author属性（其他略过）。

这里用到的是rl.question(msg, cbk)这个方法，它会在控制台输入一行提示，当用户完成输入，敲击回车，cbk就会被调用，并把用户输入作为参数传入。

const readline = require('readline');const fs = require('fs');const rl = readline.createInterface({    input: process.stdin,    output: process.stdout,    prompt: 'OHAI> '});const preHint = `This utility will walk you through creating a package.json file.It only covers the most common items, and tries to guess sensible defaults.See \`npm help json\` for definitive documentation on these fieldsand exactly what they do.Use \`npm install 
    
      --save\` afterwards to install a package andsave it as a dependency in the package.json file.Press ^C at any time to quit.`;console.log(preHint);// 问题let questions = [ 'name', 'version', 'author'];// 默认答案let defaultAnswers = [ 'name', '1.0.0', 'none' ];// 用户答案let answers = [];let index = 0;function createPackageJson(){    var map = {};    questions.forEach(function(question, index){        map[question] = answers[index];    });    fs.writeFileSync('./package.json', JSON.stringify(map, null, 4));}function runQuestionLoop() {    if(index === questions.length) {        createPackageJson();        rl.close();        return;    }    let defaultAnswer = defaultAnswers[index];    let question = questions[index] + ': (' + defaultAnswer +') ';    rl.question(question, function(answer){        answers.push(answer || defaultAnswer);        index++;        runQuestionLoop();    });}runQuestionLoop();复制代码

运行效果如下，最后还像模像样的生成了package.json（害羞脸）。

➜  commandLine git:(master) ✗ node app.jsThis utility will walk you through creating a package.json file.It only covers the most common items, and tries to guess sensible defaults.See `npm help json` for definitive documentation on these fieldsand exactly what they do.Use `npm install 
    
      --save` afterwards to install a package andsave it as a dependency in the package.json file.Press ^C at any time to quit.name: (name) helloversion: (1.0.0) 0.0.1author: (none) chyingp复制代码

写在后面