[Starson17]

Originally Posted by AlanY

sorry starson17, spoke too soon. isn't that the same as the default setting?

Yes, but it worked, so I concluded you'd damaged or replaced the default.

so, which one should i use to add

1) First name, and
2) Last name_first name?

Which one what? I only gave you one.

ok, let me explain;
i've 50 books with a mixture of filenames 1) and 2) to add to the library.

using the regex (?P<title>.+) - (?P<author>[^_]+) i got

33 books under the Authors LastName, FirstName, and
17 books under the authers FirstName LastName (with space inbetween).

so, what regex do i need to put into the 'search and replace' to 17 to the same as the other 33?

There isn't any regex that will split the FN and the LN, and reverse some, but not others. Use the regex I gave you (default) for all the FN LN format files, then click the option that reverses FN and LN (it's on the Add books regex page) and import the other group. That gives you files all in FN LN format, which is what Calibre expects. (It will create an author_sort field that is LN, FN and use it for sorting).