"tns run ios --emulator" is throwing error "Command failed: /bin/sh -c ruby -e "require 'xcodeproj';" -

this in mac , absolute newbie.i following nativescript course in pluralsight upto speed app development. have installed pre-requisites (xcode, nativescript, typescript etc.) prescribed in course.

i have created simple nativescript project button in xml page. when run command "tns run ios --emulator" in terminal, error

command failed: /bin/sh -c ruby -e "require 'xcodeproj'; xcodeproj::config.new('/users/username/rps-conf/platforms/ios/plugins-debug.xcconfig').merge(xcodeproj::config.new('/users/username/rps-conf/app/app_resources/ios/build.xcconfig')).save_as(pathname.new('/users/username/rps-conf/platforms/ios/plugins-debug.xcconfig'))" ignoring executable-hooks-1.3.2 because extensions not built. try: gem pristine executable-hooks --version 1.3.2 ignoring gem-wrappers-1.2.7 because extensions not built. try: gem pristine gem-wrappers --version 1.2.7 /users/username/.rbenv/versions/2.3.1/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in require': cannot load such file -- xcodeproj (loaderror) /users/username/.rbenv/versions/2.3.1/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:inrequire' -e:1:in `'

i have programming background (.net) understand problem rather blindly trying out automated instructions given in terminal('try gem pristine etc.')

check nativescript installition correct... try tns doctor if ok