Finding diff between current and last version

Difference between last but one commit and last commit (plus current state, if any):

git diff HEAD~

or even (easier to type)

git diff @~

where @ is the synonim for HEAD of current branch and ~ means "give me the parent of mentioned revision".

Assuming "current version" is the working directory (uncommitted modifications) and "last version" is HEAD (last committed modifications for the current branch), simply do

git diff HEAD

Credit for the following goes to user Cerran.

And if you always skip the staging area with -a when you commit, then you can simply use git diff.

Summary

1. git diff shows unstaged changes.
2. git diff --cached shows staged changes.
3. git diff HEAD shows all changes (both staged and unstaged).

Source: git-diff(1) Manual Page – Cerran

I don't really understand the meaning of "last version".

As the previous commit can be accessed with HEAD^, I think that you are looking for something like:

git diff HEAD^ HEAD

That also can be applied for a :commithash

git diff $commithash^ $commithash

As of Git 1.8.5, @ is an alias for HEAD, so you can use:

git diff @~..@

The following will also work:

git show

If you want to know the diff between head and any commit you can use:

git diff commit_id HEAD

And this will launch your visual diff tool (if configured):

git difftool HEAD^ HEAD

Since comparison to HEAD is default you can omit it (as pointed out by Orient):

git diff @^
git diff HEAD^
git diff commit_id

Warnings

• @ScottF and @Panzercrisis explain in the comments that on Windows the ~ character must be used instead of ^.

As pointed out on a comment by amalloy, if by "current and last versions" you mean the last commit and the commit before that, you could simply use

git show