You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: etsh.rb
    path of file: ./repos/homebrew-core/Formula/e
    
    the code of the file until where you have to start completion: class Etsh < F
    
  def install
    system "./configure"
    # The `tshall` target is not supported on Ubuntu 16.04 (https://etsh.nl/blog/ubuntu-16/)
    # so the `install-etshall` target must be used to only build `etshall`.
    # Check if `tshall` is supported in Ubuntu 18.04.
    install_target = OS.mac? ? "install" : "install-etshall"
    system "make", install_target, "PREFIX=#{prefix}", "SYSCONFDIR=#{etc}", "MANDIR=#{man1}"
    bin.install_symlink "etsh" => "osh"
    bin.install_symlink "tsh" => "sh6" if OS.mac?
  end