git-filter-branch - Rewrite branches

Lets you rewrite Git revision history by rewriting the branches mentioned in the <rev-list options>, applying custom filters on each revision. Those filters can modify each tree (e.g. removing a file or running a perl rewrite on all files) or information about each commit. Otherwise, all information (including original commit times or merge information) will be preserved.

The command will only rewrite the positive refs mentioned in the command line (e.g. if you pass a..b, only b will be rewritten). If you specify no filters, the commits will be recommitted without any changes, which would normally have no effect. Nevertheless, this may be useful in the future for compensating for some Git bugs or such, therefore such a usage is permitted.

NOTE: This command honors .git/info/grafts file and refs in the refs/replace/ namespace. If you have any grafts or replacement refs defined, running this command will make them permanent.

WARNING! The rewritten history will have different object names for all the objects and will not converge with the original branch. You will not be able to easily push and distribute the rewritten branch on top of the original branch. Please do not use this command if you do not know the full implications, and avoid using it anyway, if a simple single commit would suffice to fix your problem. (See the "RECOVERING FROM UPSTREAM REBASE" section in git-rebase[1] for further information about rewriting published history.)

Always verify that the rewritten version is correct: The original refs, if different from the rewritten ones, will be stored in the namespace refs/original/.

Note that since this operation is very I/O expensive, it might be a good idea to redirect the temporary directory off-disk with the -d option, e.g. on tmpfs. Reportedly the speedup is very noticeable.

Suppose you want to remove a file (containing confidential information or copyright violation) from all commits:

git filter-branch --tree-filter 'rm filename' HEAD

However, if the file is absent from the tree of some commit, a simple rm filename will fail for that tree and commit. Thus you may instead want to use rm -f filename as the script.

Using --index-filter with git rm yields a significantly faster version. Like with using rm filename, git rm --cached filename will fail if the file is absent from the tree of a commit. If you want to "completely forget" a file, it does not matter when it entered history, so we also add --ignore-unmatch:

git filter-branch --index-filter 'git rm --cached --ignore-unmatch filename' HEAD

Now, you will get the rewritten history saved in HEAD.

To rewrite the repository to look as if foodir/ had been its project root, and discard all other history:

git filter-branch --subdirectory-filter foodir -- --all

Thus you can, e.g., turn a library subdirectory into a repository of its own. Note the -- that separates filter-branch options from revision options, and the --all to rewrite all branches and tags.

To set a commit (which typically is at the tip of another history) to be the parent of the current initial commit, in order to paste the other history behind the current history:

git filter-branch --parent-filter 'sed "s/^\$/-p <graft-id>/"' HEAD

(if the parent string is empty - which happens when we are dealing with the initial commit - add graftcommit as a parent). Note that this assumes history with a single root (that is, no merge without common ancestors happened). If this is not the case, use:

git filter-branch --parent-filter \
        'test $GIT_COMMIT = <commit-id> && echo "-p <graft-id>" || cat' HEAD

or even simpler:

echo "$commit-id $graft-id" >> .git/info/grafts
git filter-branch $graft-id..HEAD

To remove commits authored by "Darl McBribe" from the history:

git filter-branch --commit-filter '
        if [ "$GIT_AUTHOR_NAME" = "Darl McBribe" ];
        then
                skip_commit "$@";
        else
                git commit-tree "$@";
        fi' HEAD

The function skip_commit is defined as follows:

skip_commit()
{
        shift;
        while [ -n "$1" ];
        do
                shift;
                map "$1";
                shift;
        done;
}

The shift magic first throws away the tree id and then the -p parameters. Note that this handles merges properly! In case Darl committed a merge between P1 and P2, it will be propagated properly and all children of the merge will become merge commits with P1,P2 as their parents instead of the merge commit.

NOTE the changes introduced by the commits, and which are not reverted by subsequent commits, will still be in the rewritten branch. If you want to throw out changes together with the commits, you should use the interactive mode of git rebase.

You can rewrite the commit log messages using --msg-filter. For example, git svn-id strings in a repository created by git svn can be removed this way:

git filter-branch --msg-filter '
        sed -e "/^git-svn-id:/d"
'

If you need to add Acked-by lines to, say, the last 10 commits (none of which is a merge), use this command:

git filter-branch --msg-filter '
        cat &&
        echo "Acked-by: Bugs Bunny <[email protected]>"
' HEAD~10..HEAD

The --env-filter option can be used to modify committer and/or author identity. For example, if you found out that your commits have the wrong identity due to a misconfigured user.email, you can make a correction, before publishing the project, like this:

git filter-branch --env-filter '
        if test "$GIT_AUTHOR_EMAIL" = "root@localhost"
        then
                [email protected]
                export GIT_AUTHOR_EMAIL
        fi
        if test "$GIT_COMMITTER_EMAIL" = "root@localhost"
        then
                [email protected]
                export GIT_COMMITTER_EMAIL
        fi
' -- --all

To restrict rewriting to only part of the history, specify a revision range in addition to the new branch name. The new branch name will point to the top-most revision that a git rev-list of this range will print.

Consider this history:

     D--E--F--G--H
    /     /
A--B-----C

To rewrite only commits D,E,F,G,H, but leave A, B and C alone, use:

git filter-branch ... C..H

To rewrite commits E,F,G,H, use one of these:

git filter-branch ... C..H --not D
git filter-branch ... D..H --not C

To move the whole tree into a subdirectory, or remove it from there:

git filter-branch --index-filter \
        'git ls-files -s | sed "s-\t\"*-&newsubdir/-" |
                GIT_INDEX_FILE=$GIT_INDEX_FILE.new \
                        git update-index --index-info &&
         mv "$GIT_INDEX_FILE.new" "$GIT_INDEX_FILE"' HEAD

git-filter-branch can be used to get rid of a subset of files, usually with some combination of --index-filter and --subdirectory-filter. People expect the resulting repository to be smaller than the original, but you need a few more steps to actually make it smaller, because Git tries hard not to lose your objects until you tell it to. First make sure that:

Then there are two ways to get a smaller repository. A safer way is to clone, that keeps your original intact.

If you really don’t want to clone it, for whatever reasons, check the following points instead (in this order). This is a very destructive approach, so make a backup or go back to cloning it. You have been warned.

git-filter-branch allows you to make complex shell-scripted rewrites of your Git history, but you probably don’t need this flexibility if you’re simply removing unwanted data like large files or passwords. For those operations you may want to consider The BFG Repo-Cleaner, a JVM-based alternative to git-filter-branch, typically at least 10-50x faster for those use-cases, and with quite different characteristics: