UNIX for Dummies Questions & Answers

Using dd or similar tools to recover data from 2 damaged cdroms, I need a way to then combine the 2 files, 1 from each cd, and make a good file: this all result from finding that certain cd's tops scratch easily even when using the "proper" cd markers, hence making the file useless, however the back up copy is the same-I am going to assume that the damage to the files are in different "bits", and attempt to recover what i can. any ideas? files are 26megs, they were originally produced in corel drawing program. I can see the holes in the cd tops.
thanks in advance.

Two is too little to be able to deduce which bits are correct -- you need more redundancy. Maybe you should have made three copies ...

If you have checksums or something then at least you could brute-force the bits you have to guess, but other than that (without knowledge of the Corel file format) it's pretty much trial and error.

Depends also on the type of error. My guess is your drive won't even let you read the sectors which are damaged, in which case you can use the noerror option of dd to continue reading. I guess it will leave zeros in those blocks, so then it should not be too hard to see if you get all the required pieces in either of the files.