What's the difference between git diff and gif diff-index

Question

When I want to get git diff files, I found someone use

git diff-index --cached  --diff-filter=AM --name-only  HEAD

and if I use

Answer 1

diff-index is a lower level operation that does less but is much faster because it doesn't look at the content, it only checks metadata like timestamps. Only Linux you can verify this with something like:

  strace -f -e file -o diff-index.log git diff-index HEAD
  wc diff-index.log
  less diff-index.log

Forget about diff-index unless you have some git performance problem to solve.

https://git-scm.com/docs/git-update-index#_using_assume_unchanged_bit

https://public-inbox.org/git/loom.20160331T143733-916@post.gmane.org/