How to (recursively) delete and ignore files/folders on github - Remove cache from tree

Background

You have mistakenly committed and even pushed unnecessary files or folders, such as .idea, .DS_Store, target folder. You now want to un-push / delete those from Github and stop tracking the changes from those files. You make a plan to delete those manually from Github, and then pull the remote changes from local repository. However, you will never see those files again from you local repo, once you pull.
You might want to keep those file in your local repo, but only want to remove them from your github.

Let’s delete those files only from Github and let those stay intact in you local repo.

1. Delete unnecessary files or folders

1.1 Files

Remove single file:

rm file.txt

Remove multiple files:

rm file1.txt file2.csv .DS_Store

Be cautious with -i flag
i tag act as a pause function and ask you to get confirm of the removal:

rm -i file.txt
rm -i file1.txt file2.csv .DS_Store

1.2 Folders / Directories

Remove empty directories:

rmdir target

Remove non-empty directories
Recursively delete whole subdirectories and files:

rmdir -R target

Be cautious with -i flag
i tag act as a pause function and ask you to get confirm of the removal:

rm -iR target

1.3 Recursively Delete certain files with the same extension (optional)

This is a bit different from 1.2 recursive.
By this, you can recursively delete all files of a specific extension in the current directory.

.xml example:

find . -name "*.xml" -type f -delete

Just to be safe, check what you are deleting by doing:

find . -name "*.xml" -type f

2. Include them in .gitignore

Check this post out for more information on gitignore file!

Example .gitignore file:

.DS_Store
target/
node_modules/
*.xml

3. Commit the changes and Checkout .gitignore

Add and commit

git add <path(s) or . for all>
git commit -m "your message"

Checkout .gitignore:

git checkout master -- .gitignore

4. Remove from git tree and then commit again!

E.g:

git rm --cached -r .DS_Store
git rm --cached -r target
git rm --cached -r node_modules