Hello, I don't understand the meaning of %s ? Is this a hash ?

No, its a string, a format string

If you use perl -MO=B::Deparse,-p myfile.pl to see how perl parses my code, you can see how that format string is the first argument to the sprintf function

I'm getting my information from an array. My problem is I don't know how many columns I'm getting.

You don't need to know, the array/code I posted knows that information, and does the right thing -- I linked a runnable example ( Re: Open multiple file handles? ) a few minutes ago in Re^3: Mysql and Perl Module