Octopress Rake Task for list categories that used on the blog.

01-task.rb

desc "List categories from existing posts (#{source_dir}/#{posts_dir}/*#{new_post_ext})"
task :categories do
  categories = []
  tags = []
  Dir.glob("./#{source_dir}/#{posts_dir}/*.markdown") do |path|
    content = File.read(path)
    next unless content =~ /\A(---\s*\n.*?\n?)^(---\s*$\n?)/m
    data = YAML.load($1)

    categories.push data["categories"] if data["categories"]
    tags.push data["tags"] if data["tags"]
  end

  puts "Categories"
  puts categories.flatten.uniq.sort.map{|d| '- ' + d}.join("\n")
end

02-example.sh

$ rake categories
Categories
- Chrome
- Flex
- Git
- HTML5
- Mac
- Octopress
- Others
- PHP
- Ruby
- Vagrant
- WordPress