ddrescue is a data recovery tool that copies data from one file or block device to another, trying to rescue the good parts first in case of read errors.
GNU ddrescue is a data recovery tool. It copies data from one file or block device (hard disk, CD-ROM, USB stick, etc) to another, trying to rescue the good parts first in case of read errors.
This tool is very popular among forensics experts because it allows the user to easily (and repeatedly) save the good parts from a damaged disk or device with certain ease.
ddrescue cannot be used as a filter i.e. in a pipe (while dd can). This is because in general it needs to jump back and forth inside the files (or block devices) to do its job.
More information and sample usage can be found in the GNU ddrescue manual.
Note that one may confuse GNU ddrescue with another tool of similar name: dd_rescue. To learn the difference between the two refer to this Ask Ubuntu answer.
