I have installed grunt-cli like this npm install -g grunt-cli. Then I copied gruntfile.js to my local project folder. I tried to run grunt command but got an error that locally installed grunt can't be found. I then installed grunt like this npm install grunt --save-dev and it worked. So my question is whether I need to install both grunt-cli and grunt?
Yes. You need a grunt on your package.json and grunt-cli on your computer (global).