Git diff between {HEAD, staged, working dir}

Question

I have a file which I have changed to add 2 new features to the systems. Now I only want to commit one of the features on the branch. So I went through the changes with git add -p and now I want to verify that I only got the parts of this one feature and that I didn't forget any. Therefore my idea was to look at the differences as diff between {HEAD, staged, working dir}.

I tried to get the right handles for the different files and then combine it with a git difftool call.

HEAD: git show HEAD:src/autosub.py --> HEAD:src/autosub.py

staged: git show :src/autosub.py --> :src/autosub.py

working dir: src/autosub.py

But the combined call does not work: git difftool HEAD:src/autosub.py :src/autosub.py src/autosub.py

What am I doing wrong? Thx!

Answer 1

git diff:

git diff [options] [<commit>] [--] [<path>...​]

It only accepts commit as arguments and is not really intended to do a diff3 with other things than commit.
You have to do it in 2 parts:

• To get the diff between your working directory and the stage : git diff[tool]
• To get the diff between the stage and HEAD : git diff[tool] --staged (or git diff --cached)

The second one is the way to see what you will commit.

You can configure diff.mnemonicPrefix to see the w (working dir), i (index/stage), or c (commit/HEAD) prefix in the diff instead of a and b.

If you really need to do a diff3 between WD/stage/HEAD:

git show HEAD:path > /tmp/head
git show :path > /tmp/staged
diff3 /tmp/head /tmp/staged path
rm /tmp/head /tmp/staged

You can put this in a shell function or a script then add it as an alias:

# Diff-3 between _C_ommit/_I_ndex/_W_orkingdir
git config --global alias.diff3ciw '! the_script'