ERROR: Error installing pg: ERROR: Failed to build gem native extension - ruby-on-rails

Question

I cloned a rails repo and i am now attempting to bundle install
Background:
OSX El Capitan
ruby 2.2.3p173 (2015-08-18 revision 51636)
[x86_64-darwin15]
rails -v Could not find gem 'pg (>= 0) ruby' in any of the gem sources listed in your Gemfile or available on this machine. Run bundle install to install missing gems.
bundle install
Fetching gem metadata from https://rubygems.org/............
Fetching version metadata from https://rubygems.org/...
Fetching dependency metadata from https://rubygems.org/..
Resolving dependencies...
Using rake 10.4.2
...
Using jbuilder 2.3.2
Using jquery-rails 4.0.5
Your user account isn't allowed to install to the system Rubygems.
You can cancel this installation and run:
bundle install --path vendor/bundle
to install the gems into ./vendor/bundle/, or you can enter your password
and install the bundled gems to Rubygems using sudo.
Password:
Installing pg 0.18.3 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
/usr/local/opt/ruby/bin/ruby -r ./siteconf20151105-3981-12lvpnr.rb extconf.rb
checking for pg_config... no
No pg_config... trying anyway. If building fails, please try again with
--with-pg-config=/path/to/pg_config
checking for libpq-fe.h... no
Can't find the 'libpq-fe.h header
*** 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
--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=/usr/local/Cellar/ruby/2.2.3/bin/$(RUBY_BASE_NAME)
--with-pg
--without-pg
--enable-windows-cross
--disable-windows-cross
--with-pg-config
--without-pg-config
--with-pg_config
--without-pg_config
--with-pg-dir
--without-pg-dir
--with-pg-include
--without-pg-include=${pg-dir}/include
--with-pg-lib
--without-pg-lib=${pg-dir}/lib
extconf failed, exit code 1
Gem files will remain installed in /var/folders/lj/c7hfzz254cd3lt2nxscv_wgw0000gn/T/bundler20151105-3981-149quvepg-0.18.3/gems/pg-0.18.3 for inspection.
Results logged to /var/folders/lj/c7hfzz254cd3lt2nxscv_wgw0000gn/T/bundler20151105-3981-149quvepg-0.18.3/extensions/x86_64-darwin-15/2.2.0/pg-0.18.3/gem_make.out
An error occurred while installing pg (0.18.3), and Bundler cannot continue.
Make sure that `gem install pg -v '0.18.3'` succeeds before bundling.
At this point I run gem install pg -v '0.18.3'
building native extensions. This could take a while...
ERROR: Error installing pg:
ERROR: Failed to build gem native extension.
/usr/local/opt/ruby/bin/ruby -r ./siteconf20151105-4004-1ylkqpt.rb extconf.rb
checking for pg_config... no
No pg_config... trying anyway. If building fails, please try again with
--with-pg-config=/path/to/pg_config
checking for libpq-fe.h... no
Can't find the 'libpq-fe.h header
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers. Check the mkmf.log file for more details. You may
need configuration options.
Provided configuration options:
--with-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=/usr/local/Cellar/ruby/2.2.3/bin/$(RUBY_BASE_NAME)
--with-pg
--without-pg
--enable-windows-cross
--disable-windows-cross
--with-pg-config
--without-pg-config
--with-pg_config
--without-pg_config
--with-pg-dir
--without-pg-dir
--with-pg-include
--without-pg-include=${pg-dir}/include
--with-pg-lib
--without-pg-lib=${pg-dir}/lib
extconf failed, exit code 1
Gem files will remain installed in /usr/local/lib/ruby/gems/2.2.0/gems/pg-0.18.3 for inspection.
Results logged to /usr/local/lib/ruby/gems/2.2.0/extensions/x86_64-darwin-15/2.2.0/pg-0.18.3/gem_make.out
My gem file has the following at the bottom
# Use sqlite3 as the database for Active Record
group :development, :test do
gem 'sqlite3'
end
group :production do
gem 'rails_12factor'
gem 'pg'
end
I'm looking at the following SO question, but cannot seem to figure out the equivalent to OSX.

Answer 1

Seems that you just don't have the Postgres installed. Install it using something like:
brew install postgres
(if you have the Homebrew)
And then try to compile the gem extensions again.