babie です。

私の環境では Ctrl-C で EXCEL.EXE は終了されます。
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$ ruby -v excel-test.rb
ruby 1.8.2 (2004-12-25) [i386-cygwin]
excel-test.rb:17: warning: literal in condition
[["a1", "b1", "c1"], ["a2", "b2", "c2"], ["a3", "b3", "c3"]]
[["a1", "b1", "c1"], ["a2", "b2", "c2"], ["a3", "b3", "c3"]]
[["a1", "b1", "c1"], ["a2", "b2", "c2"], ["a3", "b3", "c3"]]
excel-test.rb:19:in `sleep': Interrupt
        from excel-test.rb:19
----
D:\home\baba\tmp>ruby -v excel-test.rb
ruby 1.8.2 (2004-12-25) [i386-mswin32]
excel-test.rb:17: warning: literal in condition
[["a1", "b1", "c1"], ["a2", "b2", "c2"], ["a3", "b3", "c3"]]
[["a1", "b1", "c1"], ["a2", "b2", "c2"], ["a3", "b3", "c3"]]
[["a1", "b1", "c1"], ["a2", "b2", "c2"], ["a3", "b3", "c3"]]
excel-test.rb:19:in `sleep': Interrupt
        from excel-test.rb:19
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出力が溜まってしまうので sleep 1 だけ入れさせてもらいました:
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> while 1
>   p arr
    sleep 1
> end
----