add previously committed file to gitignore code example
Example 1: git remove file from repo that has been added to gitignore
Commit any files that you need to change/delete to the repo. Then:
git rm -r --cached . # this will clean all files from cache. To clean a single file, exchange '.' with filename
git add . # add all of the now uncached files that are not gitignored to the staging area
git commit -m "fix .gitignore" # commit the changes
Example 2: remove gitignore files
git ls-files --ignored --exclude-standard -z | xargs -0 git rm --cached
git commit -am "Remove ignored files"
// answer from: thSoft