How to update Xcode from 7.2.1 to 7.3.1 using terminal (commandline tools)
Depending upon the version of macOS/OS X that you have installed as well as your boot volume's storage, you might not see the version of Xcode.app in your /Applications folder update immediately after updating from the App Store app.

For a relatively easy way to deal with MAS apps and updates, check out the mas recipe in Homebrew:

https://github.com/mas-cli/mas


  A simple command line interface for the Mac App Store. Designed for scripting and automation.