# File lib/r10k/util/commands.rb, line 17
      def which(cmd)
        exts = ENV['PATHEXT'] ? ENV['PATHEXT'].split(';') : ['']
        ENV['PATH'].split(File::PATH_SEPARATOR).each do |dir|
          exts.each do |ext|
            path = File.join(dir, "#{cmd}#{ext}")
            if File.executable?(path) && File.file?(path)
              return path
            end
          end
        end
        nil
      end