What does the -f option mean for the git rm command? [duplicate]

Question

I am learning Git through this online book. I don't understand some info about the git rm command:

If you modified the file and added it to the index already, you must force the removal with the -f option. This is a safety feature to prevent accidental removal of data that hasn’t yet been recorded in a snapshot and that can’t be recovered from Git.

English is not my native language. I have some problems with correctly translating of this quote... What is "recorded in a snapshot" mean? Is it "commited"?

I see the git rm 123.txt does the same like the git rm -f 123.txt, even if 123.txt was changed and added into index (i.e. into the storage area, through the add command): it removes 123.txt from index and working directory. So, I don't understand the -f option meaning. Please, expand it for me.

Additional I tried read this:

The files being removed have to be identical to the tip of the branch, and no updates to their contents can be staged in the index, though that default behavior can be overridden with the -f option.

Also this:

-f
--force
Override the up-to-date check.

What is the "tip of the branch"? What does the -f option?

Answer 1

Try to make changes with a file in the git repo and remove it. For example:

 $ git status
 # On branch master
 # Your branch is up-to-date with 'origin/master'.
 # nothing to commit, working directory clean

 $ echo "a" >> http.c

And try to remove it:

 $ git rm http.c

you will get:

git rm http.c
error: the following file has local modifications:
    http.c

So, the -f/--force option will allow to remove it:

$ git rm -f http.c
rm 'http.c'

Answer 2

Lots of questions.

The -f is needed because git doesn't know if you want to save off your current changes before deleting. You are warned and can choose to commit before removing. that way you don't lose your progress if you decide to resurrect the file.

Adding the file moves it's changes from your working copy ( local directory), to the staging area. This is an area you can put changes and review them before committing.

git diff --staging

The record snapshot would be a commit but from what you are saying I'm wondering if staging is also considered a snapshot. I will have to try that when I'm near a computer later and update

The tip of the branch is the last commit you made to that branch.this is after you've added to staging

git commit

In short, the -f is you saying 'I don't care about changes, just remove'.