Rails will not install on my Mac - ruby-on-rails

Question

Whenever I attempt to install Rails on my Mac it works fine but immediately after when I attempt to see what version of Rails I have, the terminal says that I do not have Rails installed.
Here's what I see in my terminal:
admins-MBP-5:~ Programming$ sudo gem install rails
Building native extensions. This could take a while...
ERROR: Error installing rails:
ERROR: Failed to build gem native extension.
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby extconf.rb
checking if the C compiler accepts ... yes
checking if the C compiler accepts -Wno-error=unused-command-line-argument-hard-error-in-future... no
Building nokogiri using packaged libraries.
-----
The file "/usr/include/iconv.h" is missing in your build environment,
which means you haven't installed Xcode Command Line Tools properly.
To install Command Line Tools, try running `xcode-select --install` on
terminal and follow the instructions. If it fails, open Xcode.app,
select from the menu "Xcode" - "Open Developer Tool" - "More Developer
Tools" to open the developer site, download the installer for your OS
version and run it.
-----
*** 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=/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby
--help
--clean
--use-system-libraries
--enable-static
--disable-static
--with-zlib-dir
--without-zlib-dir
--with-zlib-include
--without-zlib-include=${zlib-dir}/include
--with-zlib-lib
--without-zlib-lib=${zlib-dir}/lib
--enable-cross-build
--disable-cross-build
Gem files will remain installed in /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.6.2 for inspection.
Results logged to /Library/Ruby/Gems/2.0.0/gems/nokogiri-1.6.6.2/ext/nokogiri/gem_make.out
admins-MBP-5:~ Programming$ rails --version
Rails is not currently installed on this system. To get the latest version, simply type:
$ sudo gem install rails
You can then rerun your "rails" command.

Answer 1

The file "/usr/include/iconv.h" is missing in your build environment,
which means you haven't installed Xcode Command Line Tools properly.
These lines tell that you haven't install XCode, it's necessary to many console utilities.
Also, you install your gems with sudo - it can cause several problems with privileges later. I recommend you to use rvm to manage ruby installations, it will save you from a lot of problems in future.

Answer 2

Learning to read your error messages is something that will help you a lot in the future.
try running `xcode-select --install` on
terminal and follow the instructions. If it fails, open Xcode.app,
select from the menu "Xcode" - "Open Developer Tool" - "More Developer
Tools" to open the developer site, download the installer for your OS
version and run it.
That text is in your own error messages, give it a shot. Once you have Xcode installed, try installing Rails again.

Answer 3

Uh, "it works fine"??? No, it doesn't, at all - the install is failing because current Rails requires the nokogiri gem.
Read and follow the directions starting from 'The file "/usr/include/iconv.h" is missing' ...