Locally installed NPM module commands can't be found - node.js

Question

For any scripts that are set up in my package.json file for modules installed locally, npm says it cannot find the command.
Below is my package.json. I have already run an ‘npm install` without any issues installing the packages.
{
"name": "app",
"private": true,
"dependencies": {
"#babel/core": "^7.8.6",
"#babel/preset-env": "^7.8.6",
"#babel/preset-react": "^7.8.3",
"babel-loader": "^8.0.6",
"bootstrap": "^4.4.1",
"jquery": "^1.9.1",
"react": "^16.13.0",
"react-dom": "^16.13.0",
"react-owl-carousel": "^2.3.1",
"react-redux": "^7.2.0",
"react-router-dom": "^5.1.2",
"react-slick": "^0.25.2",
"reactstrap": "^8.4.1",
"redux": "^4.0.5",
"redux-logger": "^3.0.6",
"redux-thunk": "^2.3.0",
"slick-carousel": "^1.8.1",
"webpack-cli": "^3.3.11"
},
"scripts": {
"postinstall": "webpack",
"start": "webpack --watch --mode=development"
},
"engines": {
"node": "10.13.0",
"npm": "6.4.1"
},
"devDependencies": {
"css-loader": "^3.4.2",
"style-loader": "^1.1.3",
"webpack": "^4.42.0"
}
}
When I try to run npm start from the root file, I get these errors:
sh: webpack: command not found
npm ERR! file sh
npm ERR! code ELIFECYCLE
npm ERR! errno ENOENT
npm ERR! syscall spawn
npm ERR! app# start: `webpack --watch --mode=development`
npm ERR! spawn ENOENT
npm ERR!
npm ERR! Failed at the app# start script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
I have this same problem across multiple projects. If I install globally it will work, but from what I understand with webpack, that should not be necessary and is discouraged: https://webpack.js.org/guides/installation/#global-installation.
Any ideas what the trouble may be here? Thanks!

Answer 1

The issue was the directory my app was located in had a / in the directory name (e.g. a/b > app > node_modules). The / is interpreted as a : and npm doesn't like that.