only run the regular expression replacement of length=... fields if the header actually contains the string 'length='. Speeds up processing of reads that don't have such a field by 20% in my trials.
only run the regular expression replacement of length=... fields if the header actually contains the string 'length='. Speeds up processing of reads that don't have such a field by 20% in my trials.

Chris7/cutadapt,marcelm/cutadapt