Can I use git diff on untracked files?

With recent git versions you can git add -N the file (or --intent-to-add), which adds a zero-length blob to the index at that location. The upshot is that your "untracked" file now becomes a modification to add all the content to this zero-length file, and that shows up in the "git diff" output.

git diffecho "this is a new file" > new.txtgit diffgit add -N new.txtgit diffdiff --git a/new.txt b/new.txtindex e69de29..3b2aed8 100644--- a/new.txt+++ b/new.txt@@ -0,0 +1 @@+this is a new file

Sadly, as pointed out, you can't git stash while you have an --intent-to-add file pending like this. Although if you need to stash, you just add the new files and then stash them. Or you can use the emulation workaround:

git update-index --add --cacheinfo \100644 e69de29bb2d1d6434b8b29ae775ad8c2e48c5391 new.txt

(setting up an alias is your friend here).

I believe you can diff against files in your index and untracked files by simply supplying the path to both files.

git diff --no-index tracked_file untracked_file

For my interactive day-to-day gitting (where I diff the working tree against the HEAD all the time, and would like to have untracked files included in the diff), add -N/--intent-to-add is unusable, because it breaks git stash.

So here's my git diff replacement. It's not a particularly clean solution, but since I really only use it interactively, I'm OK with a hack:

d() {    if test "$#" = 0; then        (            git diff --color            git ls-files --others --exclude-standard |                while read -r i; do git diff --color -- /dev/null "$i"; done        ) | `git config --get core.pager`    else        git diff "$@"    fi}

Typing just d will include untracked files in the diff (which is what I care about in my workflow), and d args... will behave like regular git diff.

Notes:

• We're using the fact here that git diff is really just individual diffs concatenated, so it's not possible to tell the d output from a "real diff" -- except for the fact that all untracked files get sorted last.
• The only problem with this function is that the output is colorized even when redirected; but I can't be bothered to add logic for that.
• I couldn't find any way to get untracked files included by just assembling a slick argument list for git diff. If someone figures out how to do this, or if maybe a feature gets added to git at some point in the future, please leave a note here!