node_modules下.bin目錄下有一個webpack.cmd腳本文件，組裝定位了要執行的webpack.js文件

"%~dp0\node.exe"  "%~dp0\..\webpack\bin\webpack.js" %*

將啓動文件指向了webpack目錄下的bin\webpack.js。

在webpack.js文件中，有一個runCommond方法和isInstalled判斷包是否安裝函數,

const runCommand = (command, args) => {
    const cp = require("child_process");
    return new Promise((resolve, reject) => {
        const executedCommand = cp.spawn(command, args, {
            stdio: "inherit",
            shell: true
        });

        executedCommand.on("error", error => {
            reject(error);
        });

        executedCommand.on("exit", code => {
            if (code === 0) {
                resolve();
            } else {
                reject();
            }
        });
    });
};
const isInstalled = packageName => {
    try {
        require.resolve(packageName);

        return true;
    } catch (err) {
        return false;
    }
};

installedClis獲取已經安裝的cli，這裏面重要的就是CLIs數組中第一行isInstalled("webpack-cli"),指向了webpack-cli。

const installedClis = CLIs.filter(cli => cli.installed);

接下來根據filter方法找到已經安裝包，處理了包路徑，通過最後的require導入了wbpack-cli/bin/cli.js

    const path = require("path");
    const pkgPath = require.resolve(`${installedClis[0].package}/package.json`);
    // eslint-disable-next-line node/no-missing-require
    const pkg = require(pkgPath);
    // eslint-disable-next-line node/no-missing-require
    require(path.resolve(
        path.dirname(pkgPath),
        pkg.bin[installedClis[0].binName]
    ));

在wbpack-cli/bin/cli.js中，是一個IIFE,一般的cli文件中一般有二個操作，處理參數，將參數交給不同的邏輯（分發業務），文件中導入webpack，創建一個webpack實例。根據參數options創建一個compile實例，掛載鈎子，

    const webpack = require("webpack");

    let lastHash = null;
    let compiler;
    try {
    compiler = webpack(options);
    } catch (err) {
    if (err.name === "WebpackOptionsValidationError") {
        if (argv.color) console.error(`\u001b[1m\u001b[31m${err.message}\u001b[39m\u001b[22m`);
        else console.error(err.message);
        // eslint-disable-next-line no-process-exit
        process.exit(1);
    }

    throw err;
    }

在文件結尾處，就找到了webpack打包入口run方法

compiler.run((err, stats) => {
    if (compiler.close) {
        compiler.close(err2 => {
            compilerCallback(err || err2, stats);
        });
    } else {
        compilerCallback(err, stats);
    }
});