[git] How to show uncommitted changes in Git and some Git diffs in detail

How do I show uncommitted changes in Git?

I STFW'ed, and these commands are not working:

teyan@TEYAN-THINK MINGW64 /d/nano/repos/PSTools/psservice (teyan/psservice)
$ git status
On branch teyan/psservice
Your branch is up-to-date with 'origin/teyan/psservice'.
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

        modified:   psservice.c
        modified:   psservice.vcxproj.filters


teyan@TEYAN-THINK MINGW64 /d/nano/repos/PSTools/psservice (teyan/psservice)
$ git diff

teyan@TEYAN-THINK MINGW64 /d/nano/repos/PSTools/psservice (teyan/psservice)
$ git diff master
fatal: ambiguous argument 'master': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'

I had a situation of git status showing changes, but git diff printing nothing, although there were changes in several lines. However:

$ git diff data.txt > myfile
$ cat myfile
<prints diff>

Git 2.20.1 on raspbian. Other commands like git checkout, git pull are printing to stdout without problems.

For me, the only thing which worked is

git diff HEAD

including the staged files, git diff --cached only shows staged files.

You have already staged the changes (presumably by running git add), so in order to get their diff, you need to run:

git diff --cached

(A plain git diff will only show unstaged changes.)

For example: