iīm losing my hair on the same issue.
i got it working - but exactly the way i want.
My files are named:
isbn_authors_title - 2nd title.pdf
so for example:
123456789_Peter Pan and Bugs Bunny_The Science of things - And other stories.pdf
so far i made it work for this scheme
123456789 - Peter Pan and Bugs Bunny - The Science of things- And other stories.pdf
The code used for this is:
(?P<isbn>.+) - (?P<author>[^_]+) - (?P<title>[^_]+)
But i didnīt get the "_" to work. Also in some cases i got a year and an edition after the title (isbn_authors_title - 2nd title_year_edition.pdf) - but as these wonīt be imported anyway (if i understood correctly).