After adding .gitignore file use following commands
git rm -r --cached .
git commit -m ".gitignore is now working"
Make sure to commit first your changes you want to keep. The –cached option will keep your files untouched on your disk though.
Other more solution:
git rm --cached `git ls-files -i --exclude-standard`
Files with space in their paths
In case you get an error message like fatal: path spec ‘…’ did not match any files, there might be files with spaces in their path. You can remove all other files with option –ignore-unmatch:
git rm --cached --ignore-unmatch `git ls-files -i --exclude-standard`
But unmatched files will remain in your repository and will have to be removed explicitly by enclosing their path with double quotes:
git rm --cached "<path.to.remaining.file>"