append custom field content to book comments

[zardoxnet]

Can anyone suggest a way to append a custom field's content to the book comments? For example, I have a custom field for the page count and I want that to be prepended to the comments field. {page_count} + " pages" + {line_break} + {current contents of the comments field}

That would be useful to be able to retain some custom field data when exporting a book to be shared to others, because that custom field information can not be seen in the saved book.

[davidfor]

Firstly, the custom field will be saved to the books metadata when you do a save-to-disk or send-to-device. Calibre updates all the metadata and another instance of calibre can read that data when you add the book to the library.

But, you can modify the core metadata fields with a metadata plugboard. These get run when calibre is sending the book outside the library. They are a template that can modify the field with other information. I do this to add information to the comments field that is not displayed on the Kobo devices. The template I use is:

program:
comment=field('comments');
rating_str = test($rating, strcat('<p><b>Rating:</b> ', rating_as_stars($rating), '</p>'),'');
kobo_last_read_str = test($#kobo_last_read,strcat('<p><b>Last Read:</b> ', $#kobo_last_read, '</p>'),'');
word_count = test(field('#words'),strcat('<b>Word count:</b> ', field('#words')),'');
page_count = test(field('#pages'),strcat('<b>Page count:</b> ', field('#pages')),'');
counts = test(strcat(word_count,page_count),'<p>','');
counts = test(word_count,strcat(counts,word_count),counts);
counts = test(word_count,test(page_count,strcat(counts,' '),counts),counts);
counts = test(page_count,strcat(counts,page_count),counts);
counts = test(strcat(word_count,page_count),strcat(counts,'</p>'),'');
extradata = strcat(rating_str,kobo_last_read_str,counts);
comment=strcat(comment,test(extradata,strcat('<hr/>',extradata),""));
re(comment, '\s+', ' ');

That adds the page count, word count, my rating and when I last read it to the comment field. The complication in it is the checking to see if the value exists and then adding tags to format it a bit better.