### Typical sequence lengths are 10-50k letters
my $sub = "CGAGCGTTGACGCNNAGCTAGT";

### Count base frequencies
while ($sub =~ /([GCATN])/g) {
    if ($1 eq 'G') { $bases{g}++; }
    if ($1 eq 'C') { $bases{c}++; }
    if ($1 eq 'A') { $bases{a}++; }
    if ($1 eq 'T') { $bases{t}++; }
    if ($1 eq 'N') { $bases{n}++; }
    }

### I need to create an array of bases to pass to rand()
my @bases = (
    ('G') x $bases{g},
    ('C') x $bases{c},
    ('A') x $bases{a},
    ('T') x $bases{t},
    ('N') x $bases{n},
);