Ruby is already installed in Mac OS X however it is highly recommended to use RVM and the best way to have RVM, Ruby, Rails and Git easily is with RailsInstaller. Go to the railsinstaller.org and just follow the instructions to download and install it. There is no need to repeat the instructions here, there is enough and very good documentation of how to proceed.
After that, you'll have all the rails environment ready. In case you want to confirm just execute the following commands:
type rvm | head -1 #Confirm RVM is installed #The output should be: # rvm is a function rails new demo cd demo rails s #Go to http://localhost:3000
Let's go with PostgreSQL which is already installed in Mac OS X Mountain Lion. Why PostgreSQL? Because it is required by Heroku. The easier way to have it running is installing Postgresapp. Download it and copy it to your Application directory and execute it.
Now the tricky part. As PostgreSQL is already installed in your Mac by default you need to make sure the OS use Postgresapp instead of the default PostgreSQL. Not doing this will cause several errors from now on.
Modify the PATH variable in your ~/.profile or ~/.bash_profile file to add the Postgres.app bin directory.
#Add PostgreSQL from Postgres.app to PATH export PATH=/Applications/Postgres.app/Contents/MacOS/bin:$PATH
To test it is running execute the following command and then install the pg gem.
which psql #/Applications/Postgres.app/Contents/MacOS/bin/psql psql --version # and try to connect to localhost psql -h localhost gem install pg
Setup Heroku first install Heroku Toolbelt. Then log in using your heroku credentials (email address and password).
$ heroku login Enter your Heroku credentials. Email: Password (typing will be hidden): Authentication successful.
Now in every RoR application you need to replace in the Gemfile the use of sqlite by pg, at least for production environment (recommended for all).