问rubygems升级语法错误

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[root@localhost rubygems-1.8.11]# uname -a
Linux localhost.localdomain 2.6.18-274.3.1.el5 #1 SMP Tue Sep 6 20:14:03 EDT 2011 i686 athlon i386 GNU/Linux

[root@localhost rubygems-1.8.11]# pwd

/home/tac/rubygems-1.8.11

[root@localhost rubygems-1.8.11]# ruby -v

ruby 1.8.5 (2006-08-25) [i386-linux]

[root@localhost rubygems-1.8.11]# ruby setup.rb

./lib/rubygems.rb:332: warning: parenthesize argument(s) for future version

./lib/rubygems.rb:514: warning: parenthesize argument(s) for future version

./lib/rubygems.rb:30:in `require': ./lib/rubygems/deprecate.rb:54: syntax error (SyntaxError)
        define_method name do |*args, &block| # TODO: really works on 1.8.7?
                                     ^

./lib/rubygems/deprecate.rb:55: syntax error

./lib/rubygems/deprecate.rb:64: syntax error

./lib/rubygems/deprecate.rb:69: syntax error    from ./lib/rubygems.rb:30
        from setup.rb:27:in `require'
        from setup.rb:27
[root@localhost rubygems-1.8.11]#