How to use rewrite with maps

Nginx has a quite powerful rewrite engine. When paired with map, it is very helpful, for example in moving to a new url scheme (as in my case).

In example below I want to have following effect:

for urls with /pref/ prefix I want to replace oldlink with newlink and old2link with new2link and leave rest of urls unchanged.

Example

http {
    map $oldseo $newseo  {
        default "--NOOP--";
        oldlink newlink;
        old2link new2link;
    }
    server {
      listen 80;
      if ( $uri ~  /pref/(.*)/ ) {
         set $oldseo $1;
      }
      if ( $newseo !~ "--NOOP--" ) {
         rewrite /pref/(.*)/ /pref/$newseo/ permanent;
         break;
      }
    }
}

How it works

Map works that way:

when you set value to first variable in map definition ( in my example $oldseo ) second variable ($newseo) gets corresponding value assigned. So instruction set $oldseo $1; Has an effect of setting $newseo as well.

I wrote that example from information I found on mailing list.