Removing folders from my rails app with rake
As mudasobwa's comment says, your using the case statement backwards. And wrongly.

You're checking if input contains letters that are not n or N, and if that's true, you delete stuff. So I could type foobar, and it'd delete files. Bad.

Even if I type exit or quit or whatever else to stop the task, it'll happily delete stuff. Even typing cancel would be interpreted as "yes, please delete stuff", since - though it contains an "n" - it contains lots of letters that are not "n".

You also have a (dead) branch for not typing y or Y, though that makes no sense. And you don't have an else branch - not that you need one, but it'd make more sense.

You have a fixme you haven't fixed. Your indentation is missing or wrong. Your message ("About to remove the tmp/letter_opener folder.") doesn't match what the code does.

In all, it's not great.

All you need is this:

namespace :cleanup do
  desc 'Deletes the emails inside tmp/letter_opener folder.'
  task letter_opener_emails: :environment do 
    puts "Remove tmp/letter_opener? [yn]"
    if STDIN.gets.chomp =~ /^y$/i
      FileUtils.rm_r("tmp/letter_opener")
    else
      puts "Aborting"
    end
  end
end