git-filter-branch(1)

NAME#

git-filter-branch - Rewrite branches

SYNOPSIS#

git filter-branch\n [--setup <command>] [--subdirectory-filter <directory>]
\n
        [--env-filter <command>] [--tree-filter <command>]
\n
        [--index-filter <command>] [--parent-filter <command>]
\n
        [--msg-filter <command>] [--commit-filter <command>]
\n
        [--tag-name-filter <command>] [--prune-empty]
\n
        [--original <namespace>] [-d <directory>] [-f | --force]
\n
        [--state-branch <branch>] [--] [<rev-list-options>...]

WARNING#

git filter-branch has a plethora of pitfalls that can produce non-obvious manglings of the intended history rewrite (and can leave you with little time to investigate such problems since it has such abysmal performance). These safety and performance issues cannot be backward compatibly fixed and as such, its use is not recommended. Please use an alternative history filtering tool such as git filter-repo[1]. If you still need to use git filter-branch, please carefully read the section called “SAFETY” (and the section called “PERFORMANCE”) to learn about the land mines of filter-branch, and then vigilantly avoid as many of the hazards listed there as reasonably possible.

DESCRIPTION#

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.

Filters#

The filters are applied in the order as listed below. The <command> argument is always evaluated in the shell context using the eval command (with the notable exception of the commit filter, for technical reasons). Prior to that, the $GIT_COMMIT environment variable will be set to contain the id of the commit being rewritten. Also, GIT_AUTHOR_NAME, GIT_AUTHOR_EMAIL, GIT_AUTHOR_DATE, GIT_COMMITTER_NAME, GIT_COMMITTER_EMAIL, and GIT_COMMITTER_DATE are taken from the current commit and exported to the environment, in order to affect the author and committer identities of the replacement commit created by git-commit-tree(1) after the filters have run.

If any evaluation of <command> returns a non-zero exit status, the whole operation will be aborted.

A map function is available that takes an "original sha1 id" argument and outputs a "rewritten sha1 id" if the commit has been already rewritten, and "original sha1 id" otherwise; the map function can return several ids on separate lines if your commit filter emitted multiple commits.

OPTIONS#

--setup <command>

--subdirectory-filter <directory>

--env-filter <command>

--tree-filter <command>

--index-filter <command>

--parent-filter <command>

--msg-filter <command>

--commit-filter <command>

As a special extension, the commit filter may emit multiple commit ids; in that case, the rewritten children of the original commit will have all of them as parents.

You can use the map convenience function in this filter, and other convenience functions, too. For example, calling skip_commit "$@" will leave out the current commit (but not its changes! If you want that, use git rebase instead).

You can also use the git_commit_non_empty_tree "$@" instead of git commit-tree "$@" if you don’t wish to keep commits with a single parent and that makes no change to the tree.

--tag-name-filter <command>

The original tags are not deleted, but can be overwritten; use "--tag-name-filter cat" to simply update the tags. In this case, be very careful and make sure you have the old tags backed up in case the conversion has run afoul.

Nearly proper rewriting of tag objects is supported. If the tag has a message attached, a new tag object will be created with the same message, author, and timestamp. If the tag has a signature attached, the signature will be stripped. It is by definition impossible to preserve signatures. The reason this is "nearly" proper, is because ideally if the tag did not change (points to the same object, has the same name, etc.) it should retain any signature. That is not the case, signatures will always be removed, buyer beware. There is also no support for changing the author or timestamp (or the tag message for that matter). Tags which point to other tags will be rewritten to point to the underlying commit.

--prune-empty

--original <namespace>

-d <directory>

-f, --force

--state-branch <branch>

<rev-list options>...

Remap to ancestor#

By using git-rev-list(1) arguments, e.g., path limiters, you can limit the set of revisions which get rewritten. However, positive refs on the command line are distinguished: we don’t let them be excluded by such limiters. For this purpose, they are instead rewritten to point at the nearest ancestor that was not excluded.

EXIT STATUS#

On success, the exit status is 0. If the filter can’t find any commits to rewrite, the exit status is 2. On any other error, the exit status may be any other non-zero value.

EXAMPLES#

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 \
\n
        'test $GIT_COMMIT = <commit-id> && echo "-p <graft-id>" || cat' HEAD

or even simpler:

git replace --graft $commit-id $graft-id
git filter-branch $graft-id..HEAD

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

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

The function skip_commit is defined as follows:

skip_commit()
{
\n
        shift;
\n
        while [ -n "$1" ];
\n
        do
\n
                shift;
\n
                map "$1";
\n
                shift;
\n
        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 '
\n
        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 '
\n
        cat &&
\n
        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 '
\n
        if test "$GIT_AUTHOR_EMAIL" = "root@localhost"
\n
        then
\n
                [email protected]
\n
        fi
\n
        if test "$GIT_COMMITTER_EMAIL" = "root@localhost"
\n
        then
\n
                [email protected]
\n
        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:

\n
     D--E--F--G--H
\n
    /     /
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 \
\n
        'git ls-files -s | sed "s-\t\"*-&newsubdir/-" |
\n
                GIT_INDEX_FILE=$GIT_INDEX_FILE.new \
\n
                        git update-index --index-info &&
\n
         mv "$GIT_INDEX_FILE.new" "$GIT_INDEX_FILE"' HEAD

CHECKLIST FOR SHRINKING A REPOSITORY#

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.

PERFORMANCE#

The performance of git-filter-branch is glacially slow; its design makes it impossible for a backward-compatible implementation to ever be fast:

The git filter-repo[1] tool is an alternative to git-filter-branch which does not suffer from these performance problems or the safety problems (mentioned below). For those with existing tooling which relies upon git-filter-branch, git filter-repo also provides filter-lamely[2], a drop-in git-filter-branch replacement (with a few caveats). While filter-lamely suffers from all the same safety issues as git-filter-branch, it at least ameliorates the performance issues a little.

SAFETY#

git-filter-branch is riddled with gotchas resulting in various ways to easily corrupt repos or end up with a mess worse than what you started with:

Also, the poor performance of git-filter-branch often leads to safety issues:

GIT#

Part of the git(1) suite

NOTES#

1.

git filter-repo

2.

filter-lamely