| rex "(?<head1>[^,]*),(?<head2>[^,]*),(?<head3>[^,]*),(?<head4>[^,]*),(?<head5>[^,]*),(?<head6>[^,]*),(?<head7>[^,]*),(?<head8>[^,]*),(?<head9>[^,]*),(?<head10>[^,]*),(?<head11>[^,]*),(?<head12>[...
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| rex "(?<head1>[^,]*),(?<head2>[^,]*),(?<head3>[^,]*),(?<head4>[^,]*),(?<head5>[^,]*),(?<head6>[^,]*),(?<head7>[^,]*),(?<head8>[^,]*),(?<head9>[^,]*),(?<head10>[^,]*),(?<head11>[^,]*),(?<head12>[^,]*)" The fields will be null so you could use fillnull to give them values e.g. | fillnull value="N/A"