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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github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();});
运行如下：
toUpperCase git:(master) node app.js Please input a word: helloYou have entered {HELLO}
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"
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]);});
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"
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']; if(line.length < command.length){ return [command.indexOf(line) === 0 ? [command] : [], line]; } 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();
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
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 <pkg> --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);let questions = [ 'name', 'version', 'author'];let defaultAnswers = [ 'name', '1.0.0', 'none' ];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();
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 <pkg> save 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
写在后面
有不少基于readline的有趣的工具，比如各种脚手架工具。限于篇幅不展开，感兴趣的同学可以研究下。
相关链接
https://nodejs.org/api/readline.html
