Math operations in regex

Question

I need to add a number to a backreference while doing a replace operation.

e.g. I am rewriting a URL

www.site.com/doc.asp?doc=321&language=1
         


        

Answer 1

That's not possible in regex. Regex only matches patterns, it doesn't do arithmetic.

The best you can do is something verbose like:

match       replace

(\d{6,})    $1
(\d{5})     1$1
(\d{4})     10$1
(\d{3})     100$1
(\d{2})     1000$1
(\d)        10000$1