Ah, I think I understand better now. You are getting the data from Excel files and you want to replicate the effect of =VLOOKUP(A9,PATENTES.xls!$A$2:$C$82,2,FALSO) on the data in a perl script.

Rather than trying to sort out how VLOOKUP works on your worksheets, it would be much easier to help if you can post the perl code you are using to read the data, a small example of the data, and a description of the result you want. It seems like you may be able to read data into a hash using "customer number" as a key and the name as the value, but I'm just guessing at this point.