Stefano:
    your way worked very well, thank you!

Robert:
    I have prolems with your code, i think is because of the way my 
bourne shell is interpreting the comand line. Beside, i prefer to code 
the solution
inside my current script (it does another things). I don't want to quote
your code in backticks because i think that would spawn two ruby 
interpreters
for this simple task.

Thank for you both!

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