Laravelがnpm run devを使用しているときに「cross-envは内部コマンドではない」とエラーを報告することを解決します.

cross-env must have updated its paths, it has "cross-env/dist/bin"not "cross-env/bin/"
in package.json (EDIT)

    "dev": "node node_modules/cross-env/dist/bin/cross-env.js NODE_ENV=development node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js",
    "watch": "node node_modules/cross-env/dist/bin/cross-env.js NODE_ENV=development node_modules/webpack/bin/webpack.js --watch --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js",
    "watch-poll": "node node_modules/cross-env/dist/bin/cross-env.js NODE_ENV=development node_modules/webpack/bin/webpack.js --watch --watch-poll --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js",
    "hot": "node node_modules/cross-env/dist/bin/cross-env.js NODE_ENV=development node_modules/webpack-dev-server/bin/webpack-dev-server.js --inline --hot --config=node_modules/laravel-mix/setup/webpack.config.js",
    "production": "node node_modules/cross-env/dist/bin/cross-env.js NODE_ENV=production node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js"

多分昔のcross-envを全部node node_modules/cross-env/dist/bin/cross-env.js置換
次の例はcsdnの文章で、たぶん上と同じです.
 

{
    "private": true,
    "scripts": {
        "dev": "npm run development",
        "development": "node node_modules/cross-env/dist/bin/cross-env.js NODE_ENV=development node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js",
        "watch": "npm run development -- --watch",
        "watch-poll": "npm run watch -- --watch-poll",
        "hot": "node node_modules/cross-env/dist/bin/cross-env.js NODE_ENV=development node_modules/webpack-dev-server/bin/webpack-dev-server.js --inline --hot --config=node_modules/laravel-mix/setup/webpack.config.js",
        "prod": "npm run production",
        "production": "node node_modules/cross-env/dist/bin/cross-env.js NODE_ENV=production node_modules/webpack/bin/webpack.js --no-progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js"
    },
    "devDependencies": {
        "axios": "^0.18",
        "bootstrap": "^4.0.0",
        "cross-env": "^5.1",
        "jquery": "^3.2",
        "laravel-mix": "^2.0",
        "lodash": "^4.17.4",
        "popper.js": "^1.12",
        "vue": "^2.5.16"
    }
}

   laravel     packae.json  cross-env  

node node_modules/cross-env/dist/bin/cross-env.js  NODE_ENV=development node_modules/webpack/bin/webpack.js

 

 
他の外国人の友人はこうしています
 
You need to make cross-env working globally instead of having it in the project.
1) remove  node_modules  folder
2) run
npm install --global cross-env
3) remove  "cross-env": "^5.0.1",  from  package.json  file  devDependencies  section. Actually, you can skip this step and keep package.json intact. If you prefer.
4) run
npm install --no-bin-links
5) run npm run dev
and see it working
P.S Tested on Windows 10 with Laravel-5.4
P.P.S Windows 10 with Laravel-5.6 does not have this problem, thus updating is an alternative solution.
laravelルートディレクトリの下でnpm run devを実行する前に、このダウンロードのためにcorss-envをグローバルにダウンロードします.
そしてpackageからjsonでcorss-env:5.0を削除します.1
その後npm install--no-bin-linksで
最後にnpm run devを実行します.
Nodeはよくわかりませんが、Laravel 5.6のnpm run dev私は第1の中でしたことに従って、直接packageを修正しました.json、私は全--globalを使っていませんから.