Smart file downloader from Apple Developer downloads area
This tool is packaged as a ruby gem. To install, run:
$ gem install adcdownload
All you need is a link to the download file (retrieve from https://developer.apple.com/download/more/)
$ adcdownload get http://adcdownload.apple.com/Developer_Tools/Xcode_8/Xcode_8.xip
adcdownload will ask you for your Apple ID, which will be cached locally.