The best OS to run Ruby on is GNU/Linux, more specifically the platform most widely used by Ruby developers and users, with the best package support, and least likely to break some ****heads expectation of your runtime environment.
At least, that's my opinion, particularly if you ever want to depend on libraries that are
impure or rely upon external programs.
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Thou shalt check the array bounds of all strings (indeed, all arrays), for surely where thou typest ``foo'' someone someday shall type ``supercalifragilisticexpialidocious''.