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    @set = (
                [ 'file00.csv', 'file01.csv', 'file02.csv', ],
...
                [ 'file08.csv', 'file09.csv', ],
                [ 'file10.csv', 'file11.csv', ],
            )

    # my $n              = 5;
    my @set;
...
        }
        $i++;
    }

#!/usr/bin/perl

...
        $z->close;
    }
}