# File lib/rubygems/commands/install_command.rb, line 43
      def execute
        ENV['GEM_PATH'] = options[:install_dir]
        if(options[:args].empty?)
          fail Gem::CommandLineError,
            "Please specify a gem name on the command line (e.g. gem build GEMNAME)"
        end
        options[:args].each do |gem_name|
          if local?
            begin
              entries = []
                if(File.exist?(gem_name) && !File.directory?(gem_name))
                  entries << gem_name
                else
                  filepattern = gem_name + "*.gem"
                  entries = Dir[filepattern] 
                end
                unless entries.size > 0
                  if options[:domain] == :local
                    alert_error "Local gem file not found: #{filepattern}"
                  end
                else
                  result = Gem::Installer.new(entries.last, options).install(options[:force],     options[:install_dir])
                  installed_gems = [result].flatten
                  say "Successfully installed #{installed_gems[0].name}, " +
                  "version #{installed_gems[0].version}" if installed_gems
              end
            rescue LocalInstallationError => e
              say " -> Local installation can't proceed: #{e.message}"
            rescue Gem::LoadError => e
              say " -> Local installation can't proceed due to LoadError: #{e.message}"
            rescue Gem::InstallError => e
              raise "Error instaling #{gem_name}:\n\t#{e.message}"
            rescue => e
              # TODO: Fix this handle to allow the error to propagate to
              # the top level handler.  Examine the other errors as
              # well.  This implementation here looks suspicious to me --
              # JimWeirich (4/Jan/05) 
              alert_error "Error installing gem #{gem_name}[.gem]: #{e.message}"
              return
            end
          end
        
          if remote? && installed_gems.nil?
            installer = Gem::RemoteInstaller.new(options)
            installed_gems = installer.install(
              gem_name,
              options[:version],
              options[:force],
              options[:install_dir])
            if installed_gems
              installed_gems.compact!
              installed_gems.each do |spec|
                say "Successfully installed #{spec.full_name}"
              end
            end
          end
        
          unless installed_gems
            alert_error "Could not install a local " +
              "or remote copy of the gem: #{gem_name}"
            terminate_interaction(1)
          end
        
          # NOTE: *All* of the RI documents must be generated first.
          # For some reason, RI docs cannot be generated after any RDoc
          # documents are generated.

          if options[:generate_ri]
            installed_gems.each do |gem|
              Gem::DocManager.new(gem, options[:rdoc_args]).generate_ri
            end
          end

          if options[:generate_rdoc]
            installed_gems.each do |gem|
              Gem::DocManager.new(gem, options[:rdoc_args]).generate_rdoc
            end
          end

          if options[:test]
            installed_gems.each do |spec|
              gem_spec = Gem::SourceIndex.from_installed_gems.search(spec.name, spec.version.version).first
              result = Gem::Validator.new.unit_test(gem_spec)
              unless result.passed?
                unless ask_yes_no("...keep Gem?", true) then
                  Gem::Uninstaller.new(spec.name, spec.version.version).uninstall
                end
              end
            end
          end
        end
      end