Webpack: After installing webpack and webpack-cli still getting error when running webpack

Seems that you had installed globally only webpack and not webpack-cli.

Therefore, npm install -g webpack-cli solves the issue.

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Explanation and alternative solutions:

Why there is the problem in the first place? The following indicates that both webpack and webpack-cli packages are locally installed:

I have the latest versions of webpack installed:

   "webpack": "^4.0.0",
   "webpack-cli": "^2.0.9"

Running webpack in your terminal cannot find your locally installed version (provided by webpack-cli since webpack-4). That's because your locals executables folder aren't included in your shell PATH variable (list of directories in which the shell looks for commands). The path where npm install executables locally is ./node_modules/.bin (more info here).

Therefore, instead of try running just webpack you need to run:

./node_modules/.bin/webpack

Also, adding to your package.json a script which use just webpack works because npm adds local ./node_modules/.bin/ directory to the shell path before it executes scripts (see npm run).

"scripts": {
    "build": "webpack"
}

Then, execute in your terminal: npm run build

In recap, I think the package.json script is the more clear and desirable way to go.

Try This command Using Npm :

npm i -g webpack-cli -D --save

In webpack version ^4.0.0 the webpack CLI was moved into a different package. Although this change has not been reflected in the docs, there is a pull request addressing that.

Carloluis's answer solve your problem, but I'd like to add that its recommended not to do global installs. So a simple npm install -D webpack-cli in your project folder will do.