grep -r demo

bash-4.2$ echo mytext > with

bash-4.2$ echo no > without

bash-4.2$ mkdir -p foo/bar

bash-4.2$ cp with* foo

bash-4.2$ cp with* foo/bar

bash-4.2$ tree
.
|-- foo
|   |-- bar
|   |   |-- with
|   |   `-- without
|   |-- with
|   `-- without
|-- with
`-- without

bash-4.2$ grep -r mytext
foo/bar/with:mytext
foo/with:mytext
with:mytext

bash-4.2$ grep -r mytext .
./foo/bar/with:mytext
./foo/with:mytext
./with:mytext

bash-4.2$ echo mytext | grep -r mytext
foo/bar/with:mytext
foo/with:mytext
with:mytext

bash-4.2$ echo no | grep -r mytext
foo/bar/with:mytext
foo/with:mytext
with:mytext

bash-4.2$ grep --version
grep (GNU grep) 2.12
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Mike Haertel and others, see <http://git.sv.gnu.org/cgit/grep.git/tree/AUTHORS>.