#! perl -slw
use strict;
use Data::Dump qw[ pp ];

my @data = map[ split ' ' ], <DATA>;
pp \@data;
my @xformed;

push @xformed, [ map shift @$_ // (), @data ] while @{ $data[ 0 ] };

pp \@xformed;

__DATA__
1 5 9 13
2 6 10 14
3 7 11 15
4 8 12 16

##</code><code>##

C:\test>1157088.pl
[[1, 5, 9, 13], [2, 6, 10, 14], [3, 7, 11, 15], [4, 8, 12, 16]]

[[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]]