Hi Ampa,
I am not sure if this really helps, since it can't replace the %20.
Nevertheless it replaces the given string with the filename.
In JavaScript this could be done like this:
result = subject.replace(/^.*\/\d{2}\s(.*)\..*$/g, "$1");
I think the best solution for the %20 is to replace these using the JavaScript replace command or using a second regular expression.
Hope it helps...
Marc