Most people need to do this only when they get a new system. I had to go through this to help out a potential brogrammer, and it would have been much easier if I pointed him to one place where he could just following direction. Instruction here applies to Mac OS X 10.6.x.

For Windows users, use the convenient installer done by guys at EngineYard from here (http://railsinstaller.org/) to install Ruby, Rails, etc., and installer from Postgres from here (http://www.postgresql.org/download/windows/) to install Postgresql.

1. Install Xcode

Xcode is included in the Mac OS X install disc. You can install from the DVD or you can down load it from here,
http://developer.apple.com/xcode/. If you already have xcode installed, you are good to go.

2. Install Git

Download and install git if you don’t have one already. Do the following and see if returns a version.

git --version

Best place is to go here (http://git-scm.com/), and download and install the latest stable release.

3. Install RVM and Ruby

RVM lets you manage set of gems for Ruby/Rails version combination. This is the best way to install Ruby and Rails. Follow the link below and install RVM and Ruby version 1.9.2 (which is latest, stable version as of this time).

curl -L get.rvm.io | bash -s stable --ruby

3.1. Then, update the .bash_profile (or whatever shell profile or rc file you need)

echo '[[ -s "$HOME/.rvm/scripts/rvm" ]] && . "$HOME/.rvm/scripts/rvm" # Load RVM function' >> ~/.bash_profile

3.2. Reload the shell.

source ~/.bash_profile

3.3. Test to see if installation was successful.

rvm list known

3.4. Install Ruby 1.9.2 (or 1.9.3)

rvm install 1.9.2

3.5. It’s probably a good to set 1.9.2 as default as well.

rvm use 1.9.2 --default

4. Install RubyGems if not already installed

Doing the following command in terminal and see if it returns version number.

gem -v

If it doesn’t return a version number, follow the steps below to install RubyGems.

4.1 Download the latest stable version from here (http://rubygems.org/pages/download)

4.2 Unzip and Install

tar xzvf rubygems-1.X.Y.tgz
cd rubygems-1.X.Y
sudo ruby setup.rb

5. Configure RVM gemset

rvm gemset create rails31

Also set default gemset.

rvm use 1.9.2@rails31 --default

6. Install Rails

Depending on what you decided above,

gem install rails -v 3.1.0

7. Install Postgresql 8.x

I’ve used MySQL mostly before, but after Oracle’s purchase of MySQL and since I deploy most of my apps on Heroku, which only supports Postgresql, I have been using Postgresql for quite sometime. For typical Rails app, it shouldn’t matter whether you use MySQL or Postgresql. You need to be careful when you need to write raw SQL statement. Postgresql is known to be more strict with the syntax.

Latest Postgresql is 9.x, but I believe pg gem only supports up to 8.x. Better stick with safe version.  Follow the link below to download and install Postgresql 8.x. Remember the admin username and password.

http://www.enterprisedb.com/products-services-training/pgdownload

pg gem will be installed when you create a Rails app with

rails new [APP NAME] -d postgresql

and install gems with

bundle install

8. Configure Postgresql for Rails

The most you have to configure is to create a user and password for each app.

8.1 Login as admin (whatever admin username you picked when you installed the Postgresql)

psql -U admin

8.2 Create a username and password for your app.

create role [USERNAME] with createdb login password '[PASSWORD]';

You would use the username and password you just created in /config/database.yml file in your Rails app.