use strict;
use warnings;
use Text::Autoformat;

my $str=qw/@/;
for my $i(1..10){
    $str = autoformat ($str, { justify => 'center' });
    print "$str\n";
    $str .= "@@" if length ($str) < 10;
    substr $str, -2, 2, '' if length ($str) > 10;
}