Pretty sure it has been answered before (in fact the manual talks about it in using regular expression section) but being from a non computer background (agriculture grad) it is kinda non obvious to me.
First I deleted all the tags in my library. Then what I have done is downloaded the only a single tag by using the goodreads metadata plug (the initial tag list bolstered by DoctorOhh's .json file, thanks for that).
So I have a single tag (which i think is most popular and hence the most logical because of wisdom of the crowd,still downloading these). I want to copy "the single tag that i will get from my goodreads plugin" into my custom made column called "Genre". I think I have to use search and replace and regular expressions but kinda lost. Any pointers or expression that i can copy paste in relevant spaces will be much appreciated.
P.S. (not really relevant but still) I had originally wanted to download the most popular tag for a book from goodreads metadata plugin eg. Historical Fiction
in tag column and then move it to the genre column. like i m doing now. then i wanted to erase the tag column and download only the 2nd most popular tag eg. Prehistoric
and somehow use a expression that transfers the 2nd most popular tag at the end of the most popular tag while adding a period(meaning .) in between eg. Historical Fiction.Prehistoric
so that I have nice hierarchical genre list like that described in the manual [http://manual.calibre-ebook.com/sub_groups.html]
But after numerous trial and errors (1st of which is if I download 2 most popular tags in goodreads metadata plugin it will display them in alphabetical order not by popularity) I think it is impossible and I suspect that may be due to website constraints. Would it not be possible to create a database made from calibre users that utilizes the efforts of its users that future users may benefit from ? If I am manually naming the genres of my 2000 book library, it would be nice to think somebody in future may benefit from, or if some earlier user had some overlap with my library, I would only have had to manually map genre of 500 books. I think the TVDB site where the database of TV shows is maintained by the users and many softwares scrape the data to benefit of its users. (i use the renamer and it is pretty handy)