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>...]'

> How to show uncommitted changes in Git

The command you are looking for is git diff.

> git diff - Show changes between commits, commit and working tree, etc

---

Here are some of the options it expose which you can use

git diff (no parameters)
Print out differences between your working directory and the index.

git diff --cached:
Print out differences between the index and HEAD (current commit).

git diff HEAD:
Print out differences between your working directory and the HEAD.

git diff --name-only
Show only names of changed files.

git diff --name-status
Show only names and status of changed files.

git diff --color-words
Word by word diff instead of line by line.

Here is a sample of the output for git diff --color-words:

---

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:

For me, the only thing which worked is

git diff HEAD

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

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.