At 10:34 PM 10/25/2001 +0900, you wrote:
>  Hi Folks,
>
>frist of all I'm new to Ruby, but I think Ruby is high on my time-table to
>learn ;-).
>
>Can you explain me the what the tr in this the Regex does?
>
>$_.tr! "A-Za-z", "N-ZA-Mn-za-m";

String#tr! does an in-place replacing of characters.  In this case, it's 
like an array mapping, where if you match a character at index 13 in 
"A-Za-z" (namely 'N'), it will replace it with the character at index 13 in 
"N-ZA-Mn-za-m" (namely 'A').

So, in irb:
irb(main):007:0> "ABCabc".tr!("A-Za-z", "N-ZA-Mn-za-m")
"NOPnop"

Jimmy