The accepted answer does not "make Git "forget" about a file..." (historically). It only makes Git ignore the file in the present/future.
This method makes Git completely forget ignored files (past/present/future), but it does not delete anything from the working directory (even when re-pulled from remote).
This method requires usage of file /.git/info/exclude
(preferred) or a pre-existing .gitignore
in all the commits that have files to be ignored/forgotten. 1
All methods of enforcing Git ignore behavior after-the-fact effectively rewrite history and thus have significant ramifications for any public/shared/collaborative repositories that might be pulled after this process. 2
General advice: start with a clean repository - everything committed, nothing pending in working directory or index, and make a backup!
Also, the comments/revision history of this answer (and revision history of this question) may be useful/enlightening.
#Commit up-to-date .gitignore (if not already existing)
#This command must be run on each branch
git add .gitignore
git commit -m "Create .gitignore"
#Apply standard Git ignore behavior only to the current index, not the working directory (--cached)
#If this command returns nothing, ensure /.git/info/exclude AND/OR .gitignore exist
#This command must be run on each branch
git ls-files -z --ignored --exclude-standard | xargs -0 git rm --cached
#Commit to prevent working directory data loss!
#This commit will be automatically deleted by the --prune-empty flag in the following command
#This command must be run on each branch
git commit -m "ignored index"
#Apply standard git ignore behavior RETROACTIVELY to all commits from all branches (--all)
#This step WILL delete ignored files from working directory UNLESS they have been dereferenced from the index by the commit above
#This step will also delete any "empty" commits. If deliberate "empty" commits should be kept, remove --prune-empty and instead run git reset HEAD^ immediately after this command
git filter-branch --tree-filter 'git ls-files -z --ignored --exclude-standard | xargs -0 git rm -f --ignore-unmatch' --prune-empty --tag-name-filter cat -- --all
#List all still-existing files that are now ignored properly
#If this command returns nothing, it's time to restore from backup and start over
#This command must be run on each branch
git ls-files --other --ignored --exclude-standard
Finally, follow the rest of this GitHub guide (starting at step 6) which includes important warnings/information about the commands below.
git push origin --force --all
git push origin --force --tags
git for-each-ref --format="delete %(refname)" refs/original | git update-ref --stdin
git reflog expire --expire=now --all
git gc --prune=now
Other developers that pull from the now-modified remote repository should make a backup and then:
#fetch modified remote
git fetch --all
#"Pull" changes WITHOUT deleting newly-ignored files from working directory
#This will overwrite local tracked files with remote - ensure any local modifications are backed-up/stashed
git reset FETCH_HEAD
1 Because /.git/info/exclude
can be applied to all historical commits using the instructions above, perhaps details about getting a .gitignore
file into the historical commit(s) that need it is beyond the scope of this answer. I wanted a proper .gitignore
file to be in the root commit, as if it was the first thing I did. Others may not care since /.git/info/exclude
can accomplish the same thing regardless where the .gitignore
file exists in the commit history, and clearly rewriting history is a very touchy subject, even when aware of the ramifications.
FWIW, potential methods may include git rebase
or a git filter-branch
that copies an external .gitignore
into each commit, like the answers to this question.
2 Enforcing Git ignore behavior after-the-fact by committing the results of a stand-alone git rm --cached
command may result in newly-ignored file deletion in future pulls from the force-pushed remote. The --prune-empty
flag in the following git filter-branch
command avoids this problem by automatically removing the previous "delete all ignored files" index-only commit. Rewriting Git history also changes commit hashes, which will wreak havoc on future pulls from public/shared/collaborative repositories. Please understand the ramifications fully before doing this to such a repository. This GitHub guide specifies the following:
Tell your collaborators to rebase, not merge, any branches they created off of your old (tainted) repository history. One merge commit could reintroduce some or all of the tainted history that you just went to the trouble of purging.
Alternative solutions that do not affect the remote repository are git update-index --assume-unchanged </path/file>
or git update-index --skip-worktree <file>
, examples of which can be found here.