Show only changed lines without syntax with git diff

Question

I have a list of usernames that are in a text file. I update this file and commit it. I am looking for a way to get a list of the changes since the last commit.

I do not want any diff formatting at all, I just want to get an output that has usernames one per line (as they are added to each commit) since the last commit.

I can't find a setting that will remove all the git diff syntax from the output so it's purely a list new lines added only.

Example

Original file:

user1
user2
user3

I then add

user4
user5

Then commit.

I want to be able to do a git diff and see only:

user4
user5

Answer 1

You could grep the diff output combining lookahead/lookbehind:

git diff --unified=0 | grep -Po '(?<=^\+)(?!\+\+).*'

• (?<=^\+) is a positive lookbehind for line starting with +
• (?!\+\+) is a negative lookahead to prevent matching files headers starting with +++ a/path/to/file.

The --unified=0 git option is just there to reduce the numbers of line to filter removing diff context, it is optional though.

There is probably better, I'm not fluent in PCRE.

Answer 2

Borrowing --unified=0 from kaiko answer I came to:

git diff HEAD^ HEAD --unified=0 | tail +6 | sed -e 's/^\+//'