#!/usr/bin/perl
use warnings;
use strict;

my ($n, $size, $dna_length) = @ARGV;

my $template = << '__EOT__';
@ns
%s
+
//%s	%d
__EOT__

open my $OUT, '>', "file$n" or die $!;
for my $i (1 .. $size) {
    my $dna = join q(), map qw( A C G T )[ rand 4 ], 1 .. $dna_length;
    my $ignored = join q(), map +('A' .. 'Z')[ rand 26 ], 1 .. 4;
    my $count = 1 + int rand 20;
    printf {$OUT} $template, $dna, $ignored, $count;
    print {$OUT} "\n" unless $i == $size;
}