Gem::Commands::SetupCommand#shebang

# File tmp/rubies/ruby-4.0.0/lib/rubygems/commands/setup_command.rb, line 283
def shebang
  if options[:env_shebang]
    ruby_name = RbConfig::CONFIG["ruby_install_name"]
    @env_path ||= ENV_PATHS.find {|env_path| File.executable? env_path }
    "#!#{@env_path} #{ruby_name}\n"
  else
    "#!#{Gem.ruby}\n"
  end
end