grep -bo

gistfile1.txt

[sheldonh@localhost etcdctl]$ cat Dockerfile
FROM golang:1.3.3-onbuild

RUN ln -s /go/bin/app /usr/bin/etcdctl

WORKDIR /

CMD ["/bin/bash"]
[sheldonh@localhost etcdctl]$ grep -bo R Dockerfile
1:R
27:R
69:R
73:R
[sheldonh@localhost etcdctl]$ grep --version
grep (GNU grep) 2.18
Copyright (C) 2014 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>.