-b
Precedes each line by the block number on which it was found. Use this flag to help find disk block numbers by context. The -b flag cannot be used with input from stdin or pipes.
-B NUM, --before-context=NUM
Print NUM lines of leading context before matching lines. Places a line
containing a group separator (--) between contiguous groups of matches. With the
-o or --only-matching option, this has no effect and a warning is given.