cannot install node-sass therefore cannot install gulp-sass

This problem typically happens if you run npm install with sudo earlier. Remove node_modules folder and run npm install without sudo

This is likely because there are permissions problems with your installation of npm:

• This page discusses general troubleshooting of these problems with npm. Complete these steps first.

• This GitHub issue describes someone fixing the exact same issue.

Try the following if you are on ubuntu:

sudo chown -R $(whoami) ~/.npm

Don't use sudo afterwards