run $ npm install [-g] shelljs
npm http GET https://registry.npmjs.org/%5B-g%5D
npm http GET https://registry.npmjs.org/shelljs
npm http 404 https://registry.npmjs.org/%5B-g%5D
npm ERR! 404 '%5B-g%5D' is not in the npm registry.
npm ERR! 404 You should bug the author to publish it
npm ERR! 404
npm ERR! 404 Note that you can also install from a
npm ERR! 404 tarball, folder, or http url, or git url.

It's on Mac OS. Any help? Thanks.