bug#18863: grep -b bug

[王琦]

Hi, I found that "grep -b" doesn't work on my machine. the expected result for 
below command is "7:not", but I got 0 $ echo gnu is not unix | grep -b -o "not" 
0:not Bash version 3.2.25 Linux version 2.6.18 Thanks. 发自邮箱大师