module TTY::Screen

def command_exist?(command)
  exts = env.fetch("PATHEXT", "").split(::File::PATH_SEPARATOR)
  env.fetch("PATH", "").split(::File::PATH_SEPARATOR).any? do |dir|
    file = ::File.join(dir, command)
    ::File.exist?(file) ||
      exts.any? { |ext| ::File.exist?("#{file}#{ext}") }
  end
end