So there you have your command line prompt from Bash/Zsh/cmd.exe and there is so called Rails console which is basically IRB prompt with the Rails application loaded.
My tip suggests that you invoke some Rails commands, namely generator related commands and rake tasks, from the running Rails console. The reason to do so is clear and simple – it’s fast.
Real World Proof
Let’s do some math to prove the point. The last project I was involved with
contains 171 models, 158 controllers and 572 migrations. Models and
controllers were mostly generated together by single
./script/generate scaffold command. Migrations were generated
with
./script/generate migration followed by
rake db:migrate command. This accounts for about 1300 command
line invocations.
Now sad statistics – running generator command from command line loads application environment which is not that cheap even on empty project
rails3_app/ > /usr/bin/time -p rails generate migration just_testing
invoke active_record
create db/migrate/20100702124738_just_testing.rb
real 7.54
user 3.40
sys 4.09
On the real world project I’m using as an example this time (because of
many gems and other dependencies) was up to one minute.
On the other hand running the same command from Rails console (i.e. with environment already loaded) is instantaneous
rails3_app/ > rails console
Loading development environment (Rails 3.0.0.beta4)
MyIrb loaded
ruby-head > time { migration 'test9' }
invoke active_record
create db/migrate/20100702125251_test9.rb
Time elapsed: 0.07000 user, 0.08000 system (0.14645 wall clock seconds)
(assuming environment loading took 30 seconds on average
one can calculate the gain from using this technique for the whole project:
30 seconds * 1300 invocations/3600 = 10.8 hours 
)
Getting/Using It
Helpers that bring generator and rake commands to IRB prompt are available
as part of my
IRB configuration
in
console_in_console.rb file.
Assuming it’s saved at ~/console_in_console.rb
rails3_app/ > rails c
ruby-head > load '~/console_in_console.rb'
ruby-head > include MyIrb::Rails::ConsoleInConsole
# Have fun now generating and destroying migrations, models, controllers
# much faster than before
ruby-head > model 'user login:string password:string'
invoke active_record
create db/migrate/20100702132016_create_users.rb
create app/models/user.rb
invoke test_unit
create test/unit/user_test.rb
create test/fixtures/users.yml
ruby-head > migration 'migration_name'
invoke active_record
create db/migrate/20100702130723_migration_name.rb
ruby-head > destroy_migration 'migration_name'
invoke active_record
remove db/migrate/20100702130723_migration_name.rb
ruby-head > rake 'db:migrate'
== Test11: migrating =========================================================
== Test11: migrated (0.0000s) ================================================
And it works with Rails 2.x branch too!