# File lib/gist.rb, line 496
  def which(cmd, path=ENV['PATH'])
    if RUBY_PLATFORM.downcase =~ /mswin(?!ce)|mingw|bccwin|cygwin/
      path.split(File::PATH_SEPARATOR).each {|dir|
        f = File.join(dir, cmd+".exe")
        return f if File.executable?(f) && !File.directory?(f)
      }
      nil
    else
      return system("which #{cmd} > /dev/null 2>&1")
    end
  end