diff command to get number of different lines only

diff can do all the first part of the job but no counting; wc -l does the rest:

diff -y --suppress-common-lines file1 file2 | wc -l

Yes you can, and in true Linux fashion you can use a number of commands piped together to perform the task.

First you need to use the diff command, to get the differences in the files.

diff file1 file2

This will give you an output of a list of changes. The ones your interested in are the lines prefixed with a '>' symbol

You use the grep tool to filter these out as follows

diff file1 file2 | grep "^>"

finally, once you have a list of the changes your interested in, you simply use the wc command in line mode to count the number of changes.

diff file1 file2 | grep "^>" | wc -l

and you have a perfect example of the philosophy that Linux is all about.