Added slim layout file and removed erb layout file

app_template.rb

### Rails app generator template. Run it:
### rails new _app_name_ -m https://gist.githubusercontent.com/DamirSvrtan/28a28e50d639b9445bbc/raw/app_template.rb

bin_setup_file = <<-FILE
#!/bin/sh
bundle install
bundle exec rake db:setup
FILE

File.open('bin/setup', 'w'){|file| file.write(bin_setup_file)}

remove_file "README.rdoc"
create_file "README.md", "Development: run ./bin/setup"
run 'mv app/assets/stylesheets/application.css app/assets/stylesheets/application.scss'

database_type = ask("Do you want to use postgres or mysql?", limited_to: ["pg", "mysql"])

adapter = if database_type == 'pg'
  gem 'pg'
  'postgresql'
else
  gem 'mysql2'
  'mysql2'
end

database_file = <<-FILE
default: &default
  adapter: <%= adapter %>
  pool: 5
  timeout: 5000
  host: localhost
  username: root

development:
  <<: *default
  database: <%= @app_name %>_development
  password:

test:
  <<: *default
  database: <%= @app_name %>_test

production:
  <<: *default
  database: <%= @app_name %>_production
FILE

File.open('config/database.yml', 'w') do |file|
  file.write(ERB.new(database_file).result(binding))
end

# Remove unwanted gems. spring will be added later in the development group of gems
%w(spring coffee-rails sqlite3).each do |unwanted_gem|
  gsub_file("Gemfile", /gem '#{unwanted_gem}'.*\n/, '')
end

# Replace erb layout file with slim layout file
layout_file = <<-FILE
doctype html
html
  head
    title Site title

    = stylesheet_link_tag    'application', media: 'all', 'data-turbolinks-track' => true
    = javascript_include_tag 'application', 'data-turbolinks-track' => true
    = csrf_meta_tags

  body
    = yield
FILE

File.delete('app/views/layouts/application.html.erb')
File.open('app/views/layouts/application.html.slim', 'w') do |file|
  file.write(ERB.new(layout_file).result(binding))
end 

# remove commented lines
gsub_file("Gemfile", /#.*\n/, '')
# remove double newlines
gsub_file("Gemfile", /^\n\n/, '')

simple_form_installation = "simple_form:install"

if yes?('Use bootstrap?')
  gem 'bootstrap-sass'
  simple_form_installation << " --bootstrap"
end

gem 'simple_form'
gem 'slim-rails'
gem 'draper'

gem_group :development do
  gem 'spring'
  gem 'better_errors'
  gem 'binding_of_caller'
  gem 'quiet_assets'
  gem 'pry-rails'
  gem 'bullet'
  gem 'traceroute'
  gem 'letter_opener'
end

run "bundle install"

generate simple_form_installation

git :init
%w(.sass-cache powder public/system dump.rdb logfile .DS_Store).each do |gitignored|
  append_file ".gitignore", gitignored
end
git add: ".", commit: "-m 'Initial commit'"

Hey, thnx for the fork, i needed this. One comment:

File.open('app/views/layouts/application.html.slim', 'w') do |file|
  file.write(ERB.new(layout_file).result(binding))
end 

Since you're not embedding any variables in the layout file, you don't need the ERB evaluation, you could just use:

File.open('app/views/layouts/application.html.slim', 'w') do |file|
  file.write(layout_file)
end 

But perhaps it would be good to have the site title set as the app name, so you could keep the ruby embedding when writing to the file, and just modify the layout_file:

layout_file = <<-FILE
doctype html
html
  head
    title <%= @app_name %>

    = stylesheet_link_tag    'application', media: 'all', 'data-turbolinks-track' => true
    = javascript_include_tag 'application', 'data-turbolinks-track' => true
    = csrf_meta_tags

  body
    = yield
FILE

I agree completely. :)