Disallow empty pattern in "git grep"
Disallow empty pattern in "git grep"

For some reason I've done a "git grep" twice with no pattern, which is
really irritating, since it just grep everything. If I actually wanted
that, I could do "git grep ^" or something.

So add a "usage" message if the pattern is empty.

Signed-off-by: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@osdl.org>
Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git