I'm not so sure that your example works as it stands. You'd need a code block to distinguish between true failure and false failure.

In perl 5.10 you could do it like:

  if ( ! /...(*COMMIT:x)(*FAIL)/ && $REGERROR ne 'x' ) { ... }
[download]

To be honest I need to think about how $REGERROR will work in the context of complete failure. For instance when failure occurs because of the optimiser. Hmm.