filter out FASTQ reads which are shorter
You need to use variable $seq. For example:

bioawk -cfastx 'length($seq)&gt;=259{print "@"$name"\n"$seq"\n+\n"$qual}' test.fq.gz


There are also more convenient tools like seqtk and seqkit. With those, you may

seqtk seq -L260 test.fq.gz