def shebang
    @shebang ||= begin
      @binstub.open(&:readline)
    rescue EOFError
      String.new("")
    end
  end
The first line of a binstub contains the "shebang" line
that tells the operating system how to execute the file
for example:

binstub = BinstubWrapper.new(Pathname.new(Dir.pwd).join("bin/rails"))
binstub.shebang # => "#!/usr/bin/env ruby\n"