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

Question

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(-)

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

git diff --stat
hg diff --stat

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.

Here is the script by suyasha all formatted correctly with line breaks, with some added message output. Good job, suyasha, should have posted your reply as an answer. I would have voted for that.

#!/bin/bash
# USAGE:    diffstat.sh [file1] [file2]

if [ ! $2 ]
then
   printf "\n   USAGE: diffstat.sh [file1] [file2]\n\n"
   exit
fi

diff -u -s "$1" "$2" > "/tmp/diff_tmp" 
add_lines=`cat "/tmp/diff_tmp" | grep ^+ | wc -l`
del_lines=`cat "/tmp/diff_tmp" | grep ^- | wc -l` 
# igonre diff header (those starting with @@) 
at_lines=`cat "/tmp/diff_tmp" | grep ^@ | wc -l`
chg_lines=`cat "/tmp/diff_tmp" | wc -l`
chg_lines=`expr $chg_lines - $add_lines - $del_lines - $at_lines` 
# subtract header lines from count (those starting with +++ & ---) 
add_lines=`expr $add_lines - 1`
del_lines=`expr $del_lines - 1`
total_change=`expr $chg_lines + $add_lines + $del_lines`
rm /tmp/diff_tmp

printf "Total added lines:  "
printf "%10s\n" "$add_lines"
printf "Total deleted lines:"
printf "%10s\n" "$del_lines"
printf "Modified lines:     "
printf "%10s\n" "$chg_lines"
printf "Total changes:      "
printf "%10s\n" "$total_change"