Include untracked files in a diff

git diff by default only takes into account the files that are already tracked. You may want to include untracked files to, e.g. when using git diff --stat to see how many lines are added and deleted.

To make git diff notice the untracked file you need to signal the

Intent to add

git add --intent-to-add [file]
git add -N [file]  # equivalend

What git add -N does is adds the [file] path to the index, without its contents (without staging it). Now, when git diff compares the file on disk to the index, all lines show up as newly added.

Include staged files in a diff

Another set of files that git diff ignores are the staged files. To change that, run it with --staged.

git add --staged