use strict;
use Data::Dumper;

my @thing = qw(a c g i t);

for my $id (1..5) {
   my (%infilestore,$seq);

   $seq .= @thing[rand @thing] for 0..2;

   push @{$infilestore{$id}}, (split //, $seq);
   print Dumper \%infilestore;
}