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first you must have install xcode and xcode commnand line tool 

then we intalll 
hombrew The best package management system on Mac OS X for this is

$ ruby -e "$(curl -fsSL https://raw.github.com/mxcl/homebrew/go)"

then we need to install git (i know you have :P )

$ brew install git

then we need to rvm (ruby version menager)

$ \curl -L https://get.rvm.io | bash -s stable

add this line in your .bash_proflie or .bashrc file 

echo '[[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm"'

reload it 

. ~/.bash_profile

now we intall ruby 1.9.3 

$ rvm install 1.9.3

in mavericks ruby 2.0 in pre install so if we want to use ruby 1.9.3 then

$ rvm use 1.9.3 

or you can make it default  for all project 
by this 

$ rvm --default use 1.9.3

cehck your ruby version 

$ ruby -v

now we install rails with specifying version 

$ gem install rails -v 3.2.14

check your rails version 
$ rails -v 

rails install sqlite databage so you don't  need to install databage :)
happy coding :)