dodged

(.+?)((\n\s.*)+)

MTN_AF

This regex will parse a line of csv data, capturing each field.

Search between Start Anchor and first word with two characters

When in Drupal you upload a file with the same filename a new file name is created with _.. The regexp is made to filter the supposedly original filename. After checking existence and filelength match the presuppostion is confirmed and deduplication takes place.