[pmwiki-users] serial number out of a pagename

[noskule]

hi list
I build serialized pages with powertools / serialname. What the best way 
to get the number out of the pagename? I want to do a pagevar $SerialNumber.

I tried with a regexpr:
Group.Name-0001
  $number = preg_replace('/-[^\d]+$/',"",$name);

I get -1 as result.
Any suggestions?
thanks nos