NAME

git-filter-branch - Rewrite branches

SYNOPSIS

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

DESCRIPTION

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

The command will only rewrite the positive refs mentioned in thecommand line (e.g. if you pass a..b, only b will be rewritten).If you specify no filters, the commits will be recommitted without anychanges, which would normally have no effect. Nevertheless, this may beuseful 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 inthe refs/replace/ namespace.If you have any grafts or replacement refs defined, running this commandwill make them permanent.

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

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

Note that since this operation is very I/O expensive, it mightbe 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 containthe 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 tothe environment, in order to affect the author and committer identities ofthe replacement commit created by git-commit-tree[1] after thefilters have run.

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

A map function is available that takes an "original sha1 id" argumentand outputs a "rewritten sha1 id" if the commit has been alreadyrewritten, and "original sha1 id" otherwise; the map function canreturn several ids on separate lines if your commit filter emittedmultiple commits.

OPTIONS

• —setup

• This is not a real filter executed for each commit but a onetime setup just before the loop. Therefore no commit-specificvariables are defined yet. Functions or variables defined herecan be used or modified in the following filter steps exceptthe commit filter, for technical reasons.

• —subdirectory-filter

• Only look at the history which touches the given subdirectory.The result will contain that directory (and only that) as itsproject root. Implies Remap to ancestor.

• —env-filter

• This filter may be used if you only need to modify the environmentin which the commit will be performed. Specifically, you mightwant to rewrite the author/committer name/email/time environmentvariables (see git-commit-tree[1] for details).

• —tree-filter

• This is the filter for rewriting the tree and its contents.The argument is evaluated in shell with the workingdirectory set to the root of the checked out tree. The new treeis then used as-is (new files are auto-added, disappeared filesare auto-removed - neither .gitignore files nor any other ignorerules HAVE ANY EFFECT!).

• —index-filter

• This is the filter for rewriting the index. It is similar to thetree filter but does not check out the tree, which makes it muchfaster. Frequently used with git rm —cached—ignore-unmatch …, see EXAMPLES below. For hairycases, see git-update-index[1].

• —parent-filter

• This is the filter for rewriting the commit’s parent list.It will receive the parent string on stdin and shall outputthe new parent string on stdout. The parent string is inthe format described in git-commit-tree[1]: empty forthe initial commit, "-p parent" for a normal commit and"-p parent1 -p parent2 -p parent3 …​" for a merge commit.

• —msg-filter

• This is the filter for rewriting the commit messages.The argument is evaluated in the shell with the originalcommit message on standard input; its standard output isused as the new commit message.

• —commit-filter

• This is the filter for performing the commit.If this filter is specified, it will be called instead of thegit commit-tree command, with arguments of the form" [(-p )…​]" and the log message onstdin. The commit id is expected on stdout.

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

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

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

• —tag-name-filter
• This is the filter for rewriting tag names. When passed,it will be called for every tag ref that points to a rewrittenobject (or to a tag object which points to a rewritten object).The original tag name is passed via standard input, and the newtag name is expected on standard output.

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

Nearly proper rewriting of tag objects is supported. If the tag hasa message attached, a new tag object will be created with the same message,author, and timestamp. If the tag has a signature attached, thesignature will be stripped. It is by definition impossible to preservesignatures. The reason this is "nearly" proper, is because ideally ifthe 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 alwaysbe removed, buyer beware. There is also no support for changing theauthor or timestamp (or the tag message for that matter). Tags which pointto other tags will be rewritten to point to the underlying commit.

• —prune-empty

• Some filters will generate empty commits that leave the tree untouched.This option instructs git-filter-branch to remove such commits if theyhave exactly one or zero non-pruned parents; merge commits willtherefore remain intact. This option cannot be used together with—commit-filter, though the same effect can be achieved by using theprovided git_commit_non_empty_tree function in a commit filter.

• —original

• Use this option to set the namespace where the original commitswill be stored. The default value is refs/original.

• -d

• Use this option to set the path to the temporary directory used forrewriting. When applying a tree filter, the command needs totemporarily check out the tree to some directory, which may consumeconsiderable space in case of large projects. By default itdoes this in the .git-rewrite/ directory but you can overridethat choice by this parameter.

• -f

• —force

• git filter-branch refuses to start with an existing temporarydirectory or when there are already refs starting withrefs/original/, unless forced.

• —state-branch

• This option will cause the mapping from old to new objects tobe loaded from named branch upon startup and saved as a newcommit to that branch upon exit, enabling incremental of largetrees. If does not exist it will be created.

• …​

• Arguments for git rev-list. All positive refs included bythese options are rewritten. You may also specify optionssuch as —all, but you must use — to separate them fromthe git filter-branch options. Implies Remap to ancestor.

Remap to ancestor

By using git-rev-list[1] arguments, e.g., path limiters, you can limit theset of revisions which get rewritten. However, positive refs on the commandline are distinguished: we don’t let them be excluded by such limiters. Forthis purpose, they are instead rewritten to point at the nearest ancestor thatwas not excluded.

EXIT STATUS

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

EXAMPLES

Suppose you want to remove a file (containing confidential informationor 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 fasterversion. Like with using rm filename, git rm —cached filenamewill fail if the file is absent from the tree of a commit. If youwant to "completely forget" a file, it does not matter when it enteredhistory, 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 projectroot, and discard all other history:

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

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

To set a commit (which typically is at the tip of anotherhistory) to be the parent of the current initial commit, inorder 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 withthe initial commit - add graftcommit as a parent). Note that this assumeshistory with a single root (that is, no merge without common ancestorshappened). 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:

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 '
    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 -pparameters. Note that this handles merges properly! In case Darlcommitted a merge between P1 and P2, it will be propagated properlyand all children of the merge will become merge commits with P1,P2as their parents instead of the merge commit.

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

You can rewrite the commit log messages using —msg-filter. Forexample, git svn-id strings in a repository created by git svn canbe 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 (noneof which is a merge), use this command:

git filter-branch --msg-filter '
    cat &&
    echo "Acked-by: Bugs Bunny <bunny@bugzilla.org>"
' HEAD~10..HEAD

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

git filter-branch --env-filter '
    if test "$GIT_AUTHOR_EMAIL" = "root@localhost"
    then
        GIT_AUTHOR_EMAIL=john@example.com
    fi
    if test "$GIT_COMMITTER_EMAIL" = "root@localhost"
    then
        GIT_COMMITTER_EMAIL=john@example.com
    fi
' -- --all

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

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 tobe smaller than the original, but you need a few more steps toactually make it smaller, because Git tries hard not to lose yourobjects until you tell it to. First make sure that:

• You really removed all variants of a filename, if a blob was movedover its lifetime. git log —name-only —follow —all — filenamecan help you find renames.

• You really filtered all refs: use —tag-name-filter cat — —allwhen calling git-filter-branch.

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

• Clone it with git clone file:///path/to/repo. The clonewill not have the removed objects. See git-clone[1]. (Notethat cloning with a plain path just hardlinks everything!)

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

• Remove the original refs backed up by git-filter-branch: say gitfor-each-ref —format="%(refname)" refs/original/ | xargs -n 1 gitupdate-ref -d.

• Expire all reflogs with git reflog expire —expire=now —all.

• Garbage collect all unreferenced objects with git gc —prune=now(or if your git-gc is not new enough to support arguments to—prune, use git repack -ad; git prune instead).

NOTES

git-filter-branch allows you to make complex shell-scripted rewritesof your Git history, but you probably don’t need this flexibility ifyou’re simply removing unwanted data like large files or passwords.For those operations you may want to considerThe BFG Repo-Cleaner,a JVM-based alternative to git-filter-branch, typically at least10-50x faster for those use-cases, and with quite differentcharacteristics:

• Any particular version of a file is cleaned exactly once. The BFG,unlike git-filter-branch, does not give you the opportunity tohandle a file differently based on where or when it was committedwithin your history. This constraint gives the core performancebenefit of The BFG, and is well-suited to the task of cleansing baddata - you don’t care where the bad data is, you just want itgone.

• By default The BFG takes full advantage of multi-core machines,cleansing commit file-trees in parallel. git-filter-branch cleanscommits sequentially (i.e. in a single-threaded manner), though itis possible to write filters that include their own parallelism,in the scripts executed against each commit.

• The command optionsare much more restrictive than git-filter branch, and dedicated justto the tasks of removing unwanted data- e.g:—strip-blobs-bigger-than 1M.

GIT

Part of the git[1] suite