Doesn't work for me.
I have my files in format: [<author>] <title>.ext, for example:
[John Doe] Mybook.pdf
and I've tried several patterns:
\[(?P<author>[^_]+)\]\s(?P<title>.+)
\[<author>\]\s(?P<title>.+)
as well as some smpler ones:
\[<author>\]\s<title>
None of them works. All result in
Title: [John Doe] Mybook
Author: Unknown
So, the author is not parsed, it is all put into the title.
I have Calibre 1.25 in Linux