ruby-analytics.rb

def counts_of_files_by_extension(dir)
  Dir["#{dir}/**/*"].reduce(Hash.new(0)) do |extension_counts, filepath|
    extension_counts[File.extname(filepath)] += 1
    extension_counts
  end
end

directory = ARGV.shift || Dir.pwd

counts = counts_of_files_by_extension(directory)
if counts.empty?
  puts 'No files found that matches your criteria.'
else
  extension_map = {
    'rb' => 'Ruby',
    'erb' => 'Ruby HTML Templates',
    'yml' => 'YAML',
    'rdoc' => 'RDoc',
    'js' => 'Javascript',
    'css' => 'CSS',
    'scss' => 'Sass',
    'coffee' => 'CoffeeScript',
  }
  puts counts.map { |k,v| "#{extension_map[k]} : #{v} Files"  }
end

@blazeeboy, compared to yours, this has the weakness of only being able to see the LAST extension, so it does not distinguish between foo.html.erb and foo.erb. On the other hand, it's O(N) with no recursion.

One minor difference from your original gist is that I don't preserve the print order of the extensions. If you want that, reduce the extension_map:
puts extension_map.reduce([]) { |s,(ext,name)| s.push("#{name} : #{counts[ext]} Files") }

Interesting points:

• Dir["**/*"] means glob all files at any depth. You can refine just like you would at shell: Dir["app/**/*.rb"]
• The glob is enumerable, so you can call reduce on it to return the hash of counts.
• Hash.new takes a default value, so you can avoid initializing when not found. Beware when using objects as the default value, as the provided argument is used for ALL defaults and you probably will be confused: Hash.new([]) should be Hash.new { |h,k| h[k] = [] }
• File has many good helpers to tear apart pieces like File.extname and File.basename
• puts ["one", "two"] will put newlines in for you!