How to remove a file from the index in git?

Question

How to remove a file from the index ( = staging area = cache) without removing it from the file system?

Answer 1

Only use git rm --cached [file] to remove a file from the index.

git reset can be used to remove added files from the index given the files are never committed.

% git add First.txt
% git ls-files
First.txt
% git commit -m "First"   
% git ls-files            
First.txt
% git reset First.txt
% git ls-files              
First.txt

NOTE: git reset First.txt has no effect on index after the commit.

Which brings me to the topic of git restore --staged . It can be used to (presumably after the first commit) remove added files from the index given the files are never committed.

% git add Second.txt              
% git status        
On branch master
Changes to be committed:
  (use "git restore --staged ..." to unstage)
    new file:   Second.txt
% git ls-files       
First.txt
Second.txt
% git restore --staged Second.txt
% git ls-files 
First.txt
% git add Second.txt 
% git commit -m "Second"
% git status            
On branch master
nothing to commit, working tree clean
% git ls-files 
First.txt         
Second.txt
Desktop/Test% git restore --staged .
Desktop/Test% git ls-files
First.txt                   
Second.txt
Desktop/Test% git reset .                    
Desktop/Test% git ls-files
First.txt
Second.txt
% git rm --cached -r .
rm 'First.txt'
rm 'Second.txt'
% git ls-files  

tl;dr Look at last 15 lines. If you don't want to be confused with first commit, second commit, before commit, after commit.... always use git rm --cached [file]