How to count differences between two files on linux?

Question

I need to work with large files and must find differences between two. And I don't need the different bits, but the number of differences.

To find the number of different rows I come up with

diff --suppress-common-lines --speed-large-files -y File1 File2 | wc -l 

And it works, but is there a better way to do it?

And how to count the exact number of differences (with standard tools like bash, diff, awk, sed some old version of perl)?

Answer 1

If you want to count the number of lines that are different use this:

diff -U 0 file1 file2 | grep ^@ | wc -l 

Doesn't John's answer double count the different lines?