bug#21414: -F string with tailing newline always matches

[Paul Eggert]

On 09/04/2015 07:45 AM, Ian Brown - HNAS wrote:
> Grep version 2.20
>
> When using the ouput of another command to pass match strings into grep using 
> -F I was getting unexpected results as it was matching every line. If the 
> terminating newline is removed the grep started to work again.
>
> Easy to work around but this is different behaviour from 2.12 and may cause 
> some scripts to fail.
>
> Ian Brown (HDS)

I assume you're referring to the following sort of behavior:

$ printf 'abc\n\ndef\n' >foo
$ grep -F 'abc
' foo
abc

def

Older versions of GNU grep would ignore the newline after 'abc' in the 
pattern, and would output only 'abc' with the above example. This 
behavior was incompatible with non-GNU grep implementations and with 
POSIX, and the incompatibility seemed to be unintended and not that 
useful and was fixed at some point (sorry, don't know the GNU grep 
version).  Sorry you were relying on it.