use 5.18.2;
my $line;
while (<DATA>){
    $line = $_;
    if ($line =~ m/(G)\1{9,}/) {
       say "$&"
    }
}

__DATA__
GGCTTTCCGTTGTTGCTGGGTGTGGGGGGCGGGCGAGATTGGAAGAGCACACGTCTGAACTCCAGTCACGCCAATATCTCGTATGCCGTCTTCTGCTTGAAAAAAGGGGTGGGGGGGAGGGGGGGCGGGGGGGGGGGGGGGAGGGGGGGAG