Gem::Installer#bash_prolog_script

# File tmp/rubies/ruby-3.1.3/lib/rubygems/installer.rb, line 985
  def bash_prolog_script
    if load_relative_enabled?
      script = +<<~EOS
        bindir="${0%/*}"
      EOS

      script << %Q(exec "$bindir/#{ruby_install_name}" "-x" "$0" "$@"\n)

      <<~EOS
        #!/bin/sh
        # -*- ruby -*-
        _=_\\
        =begin
        #{script.chomp}
        =end
      EOS
    else
      ""
    end
  end