How to? - diff returning results of only one file

Somehow I’m cross-eyed not understanding the Help and MAN pages and can’t phrase my Google search correctly (assuming what I’m looking for is a common request).

I have 2 files.
I want to diff them, but return the results of only one file (either missing or existing, doesn’t matter. If not what I want, I reason I can simply return the results of the other file).

I hope a simple, and understandable request, but I can’t seem to find the right flags. I assume this should be possible instead of returning the diff of both files and then parsing the file to remove the results of one or other file (using the angle bracket as the key character).



I am not a native English speaker, so can you repeat the question again one more time.

You mean something like;

diff --unchanged-line-format= --old-line-format= --new-line-format='%L' <file1> <file2>

Where the output will show the changes (additions) only from file2?