Capistrano recipe for creating PostgreSQL database user

capistrano-database.rb

Capistrano::Configuration.instance(true).load do
  namespace :db do
    desc "Create database user for current site"
    task :create_user, roles: :db do
      config = Pathname.new(__dir__).join("..", "database.yml")
      config = ERB.new(config.read).result(binding)
      config = YAML.load(config)
      fail "No database config for #{stage}" unless config[stage.to_s]
      username, password = config[stage.to_s].values_at("username", "password")
      run "#{sudo as: 'postgres'} psql -d postgres" do |channel, _, _|
        channel.send_data(<<-SQL)
          CREATE ROLE "#{username}" UNENCRYPTED PASSWORD '#{password}'
            NOSUPERUSER CREATEDB NOCREATEROLE INHERIT LOGIN;
        SQL
        channel.send_data("\\q\n")
      end
    end
  end
end

Expects the Capistrano MultiStage extension for the stage property, which is expected to match a Rails environment.
Also, that PostgreSQL CLI tools (psql) are installed on the server.
And that this file is located in a folder under (app-root)/config – e.g. in config/recipes/