Ignore files that have already been committed to a Git repository
If you are trying to ignore changes to a file that's already tracked in the repository (e.g. a dev.properties file that you would need to change for your local environment but you would never want to check in these changes) than what you want to do is:
git update-index --assume-unchanged <file>
If you wanna start tracking changes again
git update-index --no-assume-unchanged <file>
See git-update-index(1) Manual Page.
Also have a look at the skip-worktree and no-skip-worktree options for update-index if you need this to persist past a git-reset (via)
Update: Since people have been asking, here's a convenient (and updated since commented on below) alias for seeing which files are currently "ignored" (--assume-unchanged) in your local workspace
$ git config --global alias.ignored = !git ls-files -v | grep "^[[:lower:]]"
To untrack a file that has already been added/initialized to your repository, ie stop tracking the file but not delete it from your system use: git rm --cached filename
To untrack a single file that has already been added/initialized to your repository, i.e., stop tracking the file but not delete it from your system use: git rm --cached filename
To untrack every file that is now in your .gitignore:
First commit any outstanding code changes, and then, run this command:
git rm -r --cached .
This removes any changed files from the index(staging area), then just run:
git add .
Commit it:
git commit -m ".gitignore is now working"
To undo git rm --cached filename, use git add filename.
Make sure to commit all your important changes before running
git add .Otherwise, you will lose any changes to other files.
Please be careful, when you push this to a repository and pull from somewhere else into a state where those files are still tracked, the files will be DELETED