Originally posted by vjs
I always thought the txt was simpley overwritten and the >> was an append?
That's correct - but it all depends on the granularity. The overwrite event only takes place at the start of gmp-ecm, not at the start of a curve (when using the -c parameter - without, it's the same, of course).
Thus, the information of curve results within a single gmp-ecm run gets appended to the output file, whereas a new start of gmp-ecm naturally erases all data when using > instead of >>.