Nodejs進階：readline實現日誌分析+簡易命令行工具

本文摘錄自《Nodejs學習筆記》，更多章節及更新，請訪問 github主頁地址。歡迎加羣交流，羣號 197339705。

模塊概覽

readline是個很是實用的模塊。如名字所示，主要用來實現逐行讀取，好比讀取用戶輸入，或者讀取文件內容。常見使用場景有下面幾種，本文會逐一舉例說明。本文相關代碼可在筆者github上找到。

• 文件逐行讀取：好比說進行日誌分析。

• 自動完成：好比輸入npm，自動提示"help init install"。

• 命令行工具：好比npm init這種問答式的腳手架工具。

基礎例子

先看個簡單的例子，要求用戶輸入一個單詞，而後自動轉成大寫

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();
});

運行以下：

➜  toUpperCase git:(master) ✗ node app.js 
Please input a word: hello
You have entered {HELLO}

例子：文件逐行讀取：日誌分析

好比咱們有以下日誌文件access.log，咱們想要提取「訪問時間+訪問地址」，藉助readline能夠很方便的完成日誌分析的工做。

[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"

代碼以下：

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('訪問時間：%s %s，訪問地址：%s', arr[0], arr[1], arr[13]);
});

運行結果以下：

➜  lineByLineFromFile git:(master) ✗ node app.js
訪問時間：[2016-12-09 13:56:48.407]，訪問地址："http://www.example.com/oc/v/account/login.html"
訪問時間：[2016-12-09 14:00:10.618]，訪問地址："http://www.example.com/oc/v/account/user.html"
訪問時間：[2016-12-09 14:00:34.200]，訪問地址："http://www.example.com/oc/v/account/user.html"

例子：自動完成：代碼提示

這裏咱們實現一個簡單的自動完成功能，當用戶輸入npm時，按tab鍵，自動提示用戶可選的子命令，如help、init、install。

• 輸入np，按下tab：自動補全爲npm

• 輸入npm in，按下tab：自動提示可選子命令 init、install

• 輸入npm inst，按下tab：自動補全爲 npm install

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

function completer(line) {
    const command = 'npm';
    const subCommands = ['help', 'init', 'install'];

    // 輸入爲空，或者爲npm的一部分，則tab補全爲npm
    if(line.length < command.length){
        return [command.indexOf(line) === 0 ? [command] : [], line];
    }

    // 輸入 npm，tab提示 help init install
    // 輸入 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();

代碼運行效果以下，當輸入npm in，按下tab鍵，則會自動提示可選子命令init、install。

➜  autoComplete git:(master) ✗ node app.js
> npm in
init     install

例子：命令行工具：npmt init

下面藉助readline實現一個迷你版的npm init功能，運行腳本時，會依次要求用戶輸入name、version、author屬性（其餘略過）。

這裏用到的是rl.question(msg, cbk)這個方法，它會在控制檯輸入一行提示，當用戶完成輸入，敲擊回車，cbk就會被調用，並把用戶輸入做爲參數傳入。

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 fields
and exactly what they do.

Use \`npm install <pkg> --save\` afterwards to install a package and
save it as a dependency in the package.json file.

Press ^C at any time to quit.
`;

console.log(preHint);

// 問題
let questions = [ 'name', 'version', 'author'];

// 默認答案
let defaultAnswers = [ 'name', '1.0.0', 'none' ];

// 用戶答案
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();

運行效果以下，最後還像模像樣的生成了package.json（害羞臉）。

➜  commandLine git:(master) ✗ node app.js

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 fields
and exactly what they do.

Use `npm install <pkg> --save` afterwards to install a package and
save it as a dependency in the package.json file.

Press ^C at any time to quit.

name: (name) hello
version: (1.0.0) 0.0.1
author: (none) chyingp

寫在後面

有很多基於readline的有趣的工具，好比各類腳手架工具。限於篇幅不展開，感興趣的同窗能夠研究下。

相關連接

https://nodejs.org/api/readli...