use Modern::Perl;
use Tie::File;

{
    tie my @fastqLines, 'Tie::File', 'records.fastq', recsep => "\n" or die $!;

    my %FHs = map {
        open my $fh, '>', "$_.fastq" or die $!;
        $_ => $fh
    } qw[ TTGT GGTT ACCT ];

    for ( my $i = 0 ; $i < scalar @fastqLines ; $i += 4 ) {
        $fastqLines[ $i + 1 ] =~ /^...(.{4})/
          and print { $FHs{$1} } @fastqLines[ $i .. $i + 3 ];
    }

    untie @fastqLines;
}