Untrack files from git temporarily

Solution 1:

git update-index should do what you want

This will tell git you want to start ignoring the changes to the file
git update-index --assume-unchanged path/to/file

When you want to start keeping track again
git update-index --no-assume-unchanged path/to/file

Github Documentation: update-index

Solution 2:

you could keep your files untracked after

git rm -r --cached <file>

add your files with

git add -u

them push or do whatever you want.

Solution 3:

git rm --cached

However, you shouldn't be committing compiled binaries and external dependancies in the first place. Use a tool like Bundler to pull those in instead.