can't install vue cli code example

Example 1: install vue cli

npm install -g @vue/cli                           
//to see the version installed
vue --version

Example 2: install vue-cli

npm install -g vue-cli    //make sure you have node and npm installed 
vue init webpack <appname>  //  eg:  vue init webpack myapp
cd <appname>               // cd myapp
npm install
npm run dev  //server will start in port 8080

Example 3: npm install --global vue-cli

npm install --global vue-cli is now
npm install -g @vue/cli