If you want to be strict about your columns, then you might need to trancate strings if they are longer than the width of the column. Your example can be changed like this:

Z:\>perl
use strict;

printf STDOUT "[%-20.20s] [%20.20s]\n", 1000 .. 1001;
^D
[1000                ] [                1001]

Z:\>
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Leonid Mamtchenkov aka TVSET