If you are having issues install Ionic, you might wanna check an article I wrote on installing it: https://email@example.com/how-to-install-ionic-on-mac-without-issues-3efe92a0da93#.yh5zsay13
Here is a summary of the article:
Prerequisite: npm must be installed. You can check this by entering this command: 'npm -v'. This should give you the version number. If not please install them.
Now lets fix the issue.
First launch this command:
sudo npm install --global --unsafe-perm quickscrape
Then, launch this command:
sudo npm install -g cordova ionic --unsafe-perm quickscrape
Now, run this command:
sudo npm install -g ionic --unsafe-perm node-sass
Once I did this, Ionic worked beautifully. This was done on a MacBook Pro (Retina, 13-inch, Late 2012), running OSX El Capitan 10.11.2.
I'm not sure if Windows users have any issues with this, but I believe that you should remove the 'sudo' if you are doing this on windows.
Now that you have followed my steps, both Ionic and Cordova should be installed, and working. Start by creating a blank Ionic project:
ionic start myApp blank