Thanx for your help Theducks.
In fact i am building my pattern for the "save as" option.
I want to add the author's first name without points, without changing anything in my database, that's why i need to use the "re()" function.
But the "quality check" plugin will help me for other things for sure
Thank you !
Edit : the first name doesn't need to be extracted from author_sort, because it is allready stored in my personnal field #author_sort_firstname