How do I use postgres in a Rails app template?

It isn't needed to ask the user for the application name, as app_name is already populated with it.

Thor commands are incredibly helpful for working with files, it is possible to use .erb templates and pass them values from your template, using the template method:

# config the app to use postgresremove_file 'config/database.yml'template 'database.erb', 'config/database.yml'

database.erb:

default: &default  adapter: postgresql  host: db   port: 5432  pool: 5  timeout: 5000  user: postgres  password: postgresdevelopment:  <<: *default  database: <%= app_name %>_developmenttest:  <<: *default  database: <%= app_name %>_testproduction:  <<: *default  database: <%= app_name %>_production

I do mine a little differently. Here's my template.rb.

remove_file 'config/database.yml'file 'config/database.yml', <<-CODE  # PostgreSQL. Versions 9.1 and up are supported.  #  # Install the pg driver:  #   gem install pg  # On OS X with Homebrew:  #   gem install pg -- --with-pg-config=/usr/local/bin/pg_config  # On OS X with MacPorts:  #   gem install pg -- --with-pg-config=/opt/local/lib/postgresql84/bin/pg_config  # On Windows:  #   gem install pg  #       Choose the win32 build.  #       Install PostgreSQL and put its /bin directory on your path.  #  # Configure Using Gemfile  # gem 'pg'  #  default: &default    adapter: postgresql    encoding: unicode    # For details on connection pooling, see Rails configuration guide    # http://guides.rubyonrails.org/configuring.html#database-pooling    pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>  development:    <<: *default    database: foo_development    # The specified database role being used to connect to postgres.    # To create additional roles in postgres see `$ createuser --help`.    # When left blank, postgres will use the default role. This is    # the same name as the operating system user that initialized the database.    #username: foo    # The password associated with the postgres role (username).    #password:    # Connect on a TCP socket. Omitted by default since the client uses a    # domain socket that doesn't need configuration. Windows does not have    # domain sockets, so uncomment these lines.    #host: localhost    # The TCP port the server listens on. Defaults to 5432.    # If your server runs on a different port number, change accordingly.    #port: 5432    # Schema search path. The server defaults to $user,public    #schema_search_path: myapp,sharedapp,public    # Minimum log levels, in increasing order:    #   debug5, debug4, debug3, debug2, debug1,    #   log, notice, warning, error, fatal, and panic    # Defaults to warning.    #min_messages: notice  # Warning: The database defined as "test" will be erased and  # re-generated from your development database when you run "rake".  # Do not set this db to the same as development or production.  test:    <<: *default    database: foo_test  # As with config/secrets.yml, you never want to store sensitive information,  # like your database password, in your source code. If your source code is  # ever seen by anyone, they now have access to your database.  #  # Instead, provide the password as a unix environment variable when you boot  # the app. Read http://guides.rubyonrails.org/configuring.html#configuring-a-database  # for a full rundown on how to provide these environment variables in a  # production deployment.  #  # On Heroku and other platform providers, you may have a full connection URL  # available as an environment variable. For example:  #  #   DATABASE_URL="postgres://myuser:mypass@localhost/somedatabase"  #  # You can use this database configuration with:  #  #   production:  #     url: <%= ENV['DATABASE_URL'] %>  #  production:    <<: *default    database: foo_production    username: foo    password: <%= ENV['FOO_DATABASE_PASSWORD'] %>CODE