cp_range in_file out_file [ in_spec [out_spec] ]

   in_spec: [in_start],[in_length]
       in_start defaults to 0
       in_length defaults to -1 (rest of file)

   out_spec: [out_start],[in_length]
       out_start defaults to end of file
       out_length defaults to -1 (rest of file)

   Negative values for *_start and *_length behave as per substr.