Help required for file renaming when cleaning


I have \bibtexkey\begin{title} - \format[Replace("(.{90}).*,$1", RemoveBrackets]{\title}\end{title} for renaming pdf files when cleaning. But this does not work currently.
Found this link.
i.e., [bibtexkey] - [title]. But how to truncate the file name upto certain nuumber (say 90 or 100).
Basically, I want to replace the 1st expression to make things work, but not able to do it.