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Bad Block Scan from Terminal

How to do a bad block scan of a volume.

This reads the whole disk and reports any (hardware) errors found.

List available disks: diskutil list
Find the ID of volume to be scanned in the list, eg /dev/disk2

Enter this: sudo fsck_hfs -dylS DISKID
Example: sudo fsck_hfs -dylS /dev/disk2s2

Meaning of options...
d = output debugging info
y = assume a yes response to all questions
l = live fsck (lock down and test-only)
S = Scan disk for bad blocks