usage of String#ext ( injected by rake )

Rakefile

# coding: utf-8

require "pathname"
require "rake"


module DIR
  ROOT = Pathname(__dir__)
  ORG = ROOT.join("org")
  OUT = ROOT.join("out")
end


task :default do
  Pathname.glob(DIR::ORG.join("*.png")).each do |path|
    size = path.basename.to_s.ext("")

    out_path = DIR::OUT.join(size, "vim.png")

    mkdir_p out_path.dirname
    cp path, out_path
  end
end