bug#21159: Fails To Match Empty String

[Paul Eggert]

Squirrely wrote:
> bash$ rm empty
> > bash$ touch empty
> > bash$ # I am expecting a match, so grep should return 0.
> > bash$ grep '^$' empty
> > bash$ echo $?

Grep looks for lines that contain matches.  An empty file has no lines, so it 
cannot possibly contain any matches for any regular expression.