[Pepin33]

Thanks for your help, chaley.

The full template I'm using is this:
program: strcat(sublist(field('author'),0,1,'&'), '/', substr(raw_field('title'),0,40), ' (', field('id'), ')','/', substr(raw_field('title'),0,40), ' - ', sublist(field('author'),0,1,'&'))

To replicate directory struct in Calibre. It is:
Author's name / Title (first 40 chars) - (Calibre id) / Title (f. 40 chars) - Author

But the title's last character is lost if it's an space when I substr it. ¿?