I'd do it like this:
1) Inside the dataflow, add a lookup. Configure the lookup to redirect on no match (rather than failing).
2) Use the lookup to check whether the input row already exists.
3) Send the lookup's match output to a text file
4) Send the lookup's no-match output to the table as usual.
If you haven't even tried to resolve your issue, please don't expect the hard-working volunteers here to waste their time providing links to answers which you could easily have found yourself.