Can you get DB username, pw, database name in Rails?

From within rails you can create a configuration object and obtain the necessary information from it:

config   = Rails.configuration.database_configuration
host     = config[Rails.env]["host"]
database = config[Rails.env]["database"]
username = config[Rails.env]["username"]
password = config[Rails.env]["password"]

See the documentation for Rails::Configuration for details.

This just uses YAML::load to load the configuration from the database configuration file (database.yml) which you can use yourself to get the information from outside the rails environment:

require 'YAML'
info = YAML::load(IO.read("database.yml"))
print info["production"]["host"]
print info["production"]["database"]
...