Like dd, dd_rescue does copy data from one file or block device to another.
You can specify file positions (called seek and Skip in dd).
There are several differences:
* dd_rescue does not provide character conversions.
* The command syntax is different. Call dd_rescue -h.
* dd_rescue does not abort on errors on the input file, unless you specify a
maximum error number. Then dd_rescue will abort when this number is
reached.
* dd_rescue does not truncate the output file, unless asked to.
* You can tell dd_rescue to start from the end of a file and move backwards.
* It uses two block sizes, a large (soft) block size and a small (hard) block
size. In case of errors, the size falls back to the small one and is
promoted again after a while without errors.
