How do you diff a directory for only files of a specific type?

Question

I have a question about the diff command if I want a recursive directory diff but only for a specific file type, how to do that?

I tried using the exclude option but can

Answer 1

The lack of a complementary --include ... .

We can do one workaround, a exclude file with all files but what we want include. So we create file1 with a find all files which don't have extensions that we want include, sed catch the filename and is just :

diff --exclude-from=file1  PATH1/ PATH2/

For example:

find  PATH1/ -type f | grep --text -vP "php$|html$" | sed 's/.*\///' | sort -u > file1 
diff PATH1/ PATH2/ -rq -X file1