busunsl is right, but I'd like to add another feature and DWIM[1] to your code: 
s/(SUM(\d*))/&sum($2)/eg

[download]
For I think you want to have the SUM characters stripped off, don't you?

[1] Do What I Mean
--
Alfie

In reply to Re: Subroutines in a regex? by alfie
in thread Subroutines in a regex? by heidkamp

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