Generator commands delegate Rails::Generator::Base and implement a standard set of actions. Their behavior is defined by the way they respond to these actions: Create brings life; Destroy brings death; List passively observes.

Commands are invoked by replaying (or rewinding) the generator‘s manifest of actions. See Rails::Generator::Manifest and Rails::Generator::Base#manifest method that generator subclasses are required to override.

Commands allows generators to "plug in" invocation behavior, which corresponds to the GoF Strategy pattern.

Methods
Public Instance methods
class_collisions(*class_names)

Does nothing for all commands except Create.

Source: show | on GitHub 

    # File railties/lib/rails_generator/commands.rb, line 53
53:         def class_collisions(*class_names)
54:         end
dependency(generator_name, args, runtime_options = {})

Source: show | on GitHub 

    # File railties/lib/rails_generator/commands.rb, line 46
46:         def dependency(generator_name, args, runtime_options = {})
47:           logger.dependency(generator_name) do
48:             self.class.new(instance(generator_name, args, full_options(runtime_options))).invoke!
49:           end
50:         end
invoke!()

Replay action manifest. RewindBase subclass rewinds manifest.

Source: show | on GitHub 

    # File railties/lib/rails_generator/commands.rb, line 41
41:         def invoke!
42:           manifest.replay(self)
43:           after_generate
44:         end
readme(*args)

Does nothing for all commands except Create.

Source: show | on GitHub 

    # File railties/lib/rails_generator/commands.rb, line 57
57:         def readme(*args)
58:         end
Protected Instance methods
current_migration_number()

Source: show | on GitHub 

    # File railties/lib/rails_generator/commands.rb, line 61
61:           def current_migration_number
62:             Dir.glob("#{RAILS_ROOT}/#{@migration_directory}/[0-9]*_*.rb").inject(0) do |max, file_path|
63:               n = File.basename(file_path).split('_', 2).first.to_i
64:               if n > max then n else max end
65:             end
66:           end
existing_migrations(file_name)

Source: show | on GitHub 

    # File railties/lib/rails_generator/commands.rb, line 76
76:           def existing_migrations(file_name)
77:             Dir.glob("#{@migration_directory}/[0-9]*_*.rb").grep(/[0-9]+_#{file_name}.rb$/)
78:           end
gsub_file(relative_destination, regexp, *args, &block)

Source: show | on GitHub 

    # File railties/lib/rails_generator/commands.rb, line 92
92:           def gsub_file(relative_destination, regexp, *args, &block)
93:             path = destination_path(relative_destination)
94:             content = File.read(path).gsub(regexp, *args, &block)
95:             File.open(path, 'wb') { |file| file.write(content) }
96:           end
migration_directory(relative_path)

Source: show | on GitHub 

    # File railties/lib/rails_generator/commands.rb, line 72
72:           def migration_directory(relative_path)
73:             directory(@migration_directory = relative_path)
74:           end
migration_exists?(file_name)

Source: show | on GitHub 

    # File railties/lib/rails_generator/commands.rb, line 80
80:           def migration_exists?(file_name)
81:             not existing_migrations(file_name).empty?
82:           end
next_migration_number()

Source: show | on GitHub 

    # File railties/lib/rails_generator/commands.rb, line 68
68:           def next_migration_number
69:             current_migration_number + 1
70:           end
next_migration_string(padding = 3)

Source: show | on GitHub 

    # File railties/lib/rails_generator/commands.rb, line 84
84:           def next_migration_string(padding = 3)
85:             if ActiveRecord::Base.timestamped_migrations
86:               Time.now.utc.strftime("%Y%m%d%H%M%S")
87:             else
88:               "%.#{padding}d" % next_migration_number
89:             end
90:           end