How to get diff to report summary of new, changed and deleted lines

For those using Git or Mercurial, a quick way to see such a summary of ones unstaged changes:

git diff --stat
hg diff --stat

I think you are looking for diffstat. Simply pipe the output of diff -u to diffstat and you should get something like this.

 include/net/bluetooth/l2cap.h |    6 ++++++
 net/bluetooth/l2cap.c         |   18 +++++++++---------
 2 files changed, 15 insertions(+), 9 deletions(-)

If you use diff -u it will generate a unified diff that has lines preceded with + and -. If you pipe that output through grep (to get only the + or -) and then to wc you get the counts for the + es and the - es respectively.