Using .slugignore to reduce your slug size

This may be old news to some, but I recently learned about a cool Heroku feature: the .slugignore file.

What is it? A .slugignore is like a .gitignore file for your app. It is used to reduce the size of your slug file on Heroku by ignoring files that are not essential for your app to operate.

Why is it cool? The smaller the slug file for your app, the faster Heroku can transfer it across dynos, making scaling much easier. Heroku suggests keeping your slug file size under 50MB, files smaller than 15MB are preferred.

How do I use it? Place it in your project’s root folder. It works the same way as a .gitignore file does. The only difference is that it doesn’t support the negation operator (!). Here are some suggestions of things that you may want to put in your .slugignore file:

• Mockups and old versions of image assets
• Any project documents, PDF’s, etc.
• Test files

Example .slugignore

test
docs
*.pdf

This one had me “stumped” for awhile. When using motion-stump mocks, you need to clear them in an after block like this:

after do
  Stump::Mocks.clear!
end

Someone has submitted a pull request” to motion-stump for this to happen automatically but it hasn’t been merged yet.

I always forget the syntax for this:

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ary = [:a, 1, :b, 2, :c, 3]
Hash[*ary] # => { :a => 1, :b => 2, :c => 3 }

I just started learning about sed and came across one “gotcha” when using the -i option in OS X. The -i option allows you to edit a file in-place. It takes an optional parameter - a string to use as the extension for the backup file. If this parameter is not provided, then a backup file is not created.

I was using sed to remove some tag references from a ctags file. Since the file could easily be re-generated I didn’t feel the need to provide a backup extension. I tried to execute the command below, but received an error:

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→ sed -i "/lib\/timekeeper\/employee.rb/d" tags
sed: 1: "tags": undefined label 'ags'

After some head scratching and Googling I figured out that in OS X the parameter is not optional, so the correct command is this:

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→ sed -i "" "/lib\/timekeeper\/employee.rb/d" tags

I prefer Ruby’s Test::Unit over RSpec, but one of the things I like about RSpec is the let method. It allows you to create memoized helper methods in your tests.

Here’s a way to do that in Test::Unit:

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class Test::Unit::TestCase
  def self.let(name, &block)
    ivar = "@#{name}"
    self.class_eval do
      define_method(name) do
        if instance_variable_defined?(ivar)
          instance_variable_get(ivar)
        else
          value = self.instance_eval(&block)
          instance_variable_set(ivar, value)
        end
      end
    end
  end
end

Now instead of writing helper methods in your tests like this…

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class EmployeeTest < Test::Unit::TestCase
  def test_employee_has_an_email
    assert_equal('jdoe@example.com', employee.email)
  end

  private

  def employee
    @employee ||= Employee.new('jdoe@example.com')
  end
end

You can use “let” like this…

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class EmployeeTest < Test::Unit::TestCase
  let(:employee) { Employee.new('jdoe@example.com') }

  def test_employee_has_an_email
    assert_equal('jdoe@example.com', employee.email)
  end
end

I’ve been playing around with the LinkedIn API and Sinatra for about a week and wrote a tiny app. After you authenticate using your LinkedIn credentials, the app allows you to search your connections for those that have a skill you specify. I have a working example up on Heroku at and the source code can be found on GitHub.

Since this was more about using the LinkedIn API gem with Sinatra the matching algorithm is very naive. One interesting thing I found though is the amatch gem which is a set of extensions that allow you to do approximate matching, searching and comparing of strings. In the app I used the gem’s Jaro-Winkler metric to compare the search term.

I already mentioned in a previous post how to generate ctags for a Rails app. You can also use the gem-browse and gem-ctags gems to automatically generate a ctags file every time you install a new gem.

I always forget how to set up ctags for a Ruby/Rails app so that I get tags for not only the project, but also any gems specified in my Gemfile. From the project root do:

ctags -R `bundle show rails`/../* .

Sidestep is an experiement built using Sinatra and jQTouch. It’s a mobile web app that provides NJTransit train information. The source code is available on GitHub and a working example is on Heroku.