use Data::Dumper;
use strict;

my @data;
my $cur_index;
open(DATA, "<", "data.txt");
while (<DATA>) {
    #chomp;
    if (m/^>DATA SET (\d+)/) {
        $cur_index = $1;
    } else {
        $data[$cur_index] .= $_;
    }
}
close(DATA);
print Dumper(@data);