What if you want to generate reasonably short alphanumeric user activation codes without having to store anything in a DB (so in this case generating random user codes won’t do) ? Why would someone need this? Think about an application where you want to print activation cards and sell them to your customers. The customer then login to your website, put the activation code that is printed on its card… and bingo : they are activated.
So, how to do this? With encryption, of course.
The thing is that most encryption algorithms will generate ciphers with non-friendly characters, like : Òèç`{&[ùỲgǛ… so bad for readability. It seems complicated at first but finally one solution turns out to be fairly simple :
Step #1

sudo gem install crypt

Step #2

blowfish = Crypt::Blowfish.new(SOME_KEY)
crypted_but_readable = blowfish.encrypt_block("12345678").unpack("H*")

Step #3

  crypted_block = params[:some_crypted_but_readable_block].to_s
  if crypted_block.length == 16
    blowfish = Crypt::Blowfish.new(THE_SAME_KEY)
    decrypted_block = blowfish.decrypt_block(crypted_block.to_a.pack("H*"))
    #do something with decrypted block
  end

The Blowfish algorithm takes 8-bytes blocks only… so you have to take that into account when you generate your keys. The unpack(“H*) and pack(“H*”) parts are the most important. It simply encodes/decodes the block in hexadecimal. So, here we are, you have a readable & decryptable 16-chars cipher that looks like : 9048bb8f56eddd47. You can even display the codes into chunks of 4 characters and it gives you the following friendly code : 9048-bb8f-56ed-dd47
Tip: Associate to each code a SHA-1 hashed password (which is the result of activation code + some salt) and you have a pretty safe account activation procedure that doesn’t pollute your database.

When you are developing an app or a website for your client, it is pretty common to setup a sandbox environment where your client can test and see the application while it is still in development. One thing I find useful is to display the last deployment date on the home page.
Here is a quick and easy way to automate the process :
Step #1 (we can have lots of fun)
I will consider that you use capistrano for deploying your app. The only thing you have to do in your capistrano recipe is to “touch” a dummy file to update its modification date.

namespace :deploy do
  desc 'Restart My App'
  task :restart, :roles => :app do
    run "touch #{current_path}/last_deploy"
  end
end

Step #2 (there’s so much we can do)
Now in application_controller, add a before_filter like this

before_filter :last_deploy
def last_deploy
  @last_deploy = File.new("last_deploy").atime rescue Time.now
end

Step #3 (it’s just you and me)
Display the date in the layout or in the view of your choice

<%= "Last deployment : #{@last_deploy}"%>

Edit : Oh, dear readers, I just want to let you know that RubyFleebie is now on Twitter.