Command line gem install error - sqlite3 - Rails New Command - ruby-on-rails

Question

I tried creating a new rails application in command line and had the following error. What's the problem?
I have tried working it out myself, but I'm new to coding and even reading through it I'm completely lost!
/Users/johnsway/.rvm/rubies/ruby-2.1.2/bin/ruby extconf.rb
checking for sqlite3.h... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers. Check the mkmf.log file for more details. You may
need configuration options.
Provided configuration options:
--with-opt-dir
--without-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=/Users/johnsway/.rvm/rubies/ruby-2.1.2/bin/ruby
--with-sqlite3-dir
--without-sqlite3-dir
--with-sqlite3-include
--without-sqlite3-include=${sqlite3-dir}/include
--with-sqlite3-lib
--without-sqlite3-lib=${sqlite3-dir}/lib
/Users/johnsway/.rvm/rubies/ruby-2.1.2/lib/ruby/2.1.0/mkmf.rb:456:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
from /Users/johnsway/.rvm/rubies/ruby-2.1.2/lib/ruby/2.1.0/mkmf.rb:587:in `try_cpp'
from /Users/johnsway/.rvm/rubies/ruby-2.1.2/lib/ruby/2.1.0/mkmf.rb:1120:in `block in find_header'
from /Users/johnsway/.rvm/rubies/ruby-2.1.2/lib/ruby/2.1.0/mkmf.rb:918:in `block in checking_for'
from /Users/johnsway/.rvm/rubies/ruby-2.1.2/lib/ruby/2.1.0/mkmf.rb:351:in `block (2 levels) in postpone'
from /Users/johnsway/.rvm/rubies/ruby-2.1.2/lib/ruby/2.1.0/mkmf.rb:321:in `open'
from /Users/johnsway/.rvm/rubies/ruby-2.1.2/lib/ruby/2.1.0/mkmf.rb:351:in `block in postpone'
from /Users/johnsway/.rvm/rubies/ruby-2.1.2/lib/ruby/2.1.0/mkmf.rb:321:in `open'
from /Users/johnsway/.rvm/rubies/ruby-2.1.2/lib/ruby/2.1.0/mkmf.rb:347:in `postpone'
from /Users/johnsway/.rvm/rubies/ruby-2.1.2/lib/ruby/2.1.0/mkmf.rb:917:in `checking_for'
from /Users/johnsway/.rvm/rubies/ruby-2.1.2/lib/ruby/2.1.0/mkmf.rb:1119:in `find_header'
from extconf.rb:30:in `<main>'
extconf failed, exit code 1
If you need anything else, please feel free to ask!
Thank you for your help!

Answer 1

Perhaps this problem has to do with a recent update of XCode. After a XCode update you need to do the following steps:
Open Xcode and accept the license agreement
Reinstall the Command Line Tools.
The second step seems to depend on your OS versions. If xcode-select --install does not work try to start the Install Command Line Developer Tools app in /System/Library/CoreServices.
After reinstalling the Command Line Tools try to rerun bundle install.