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GIT\-FILTER\-BRANCH

Section: Git Manual (1)
Updated: 09/30/2007
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NAME

git-filter-branch - Rewrite branches  

SYNOPSIS

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

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 (i.e. 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.

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.

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 extensively 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 shell 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 set according to the current commit.

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

--env-filter <command>

This is the filter for modifying the environment in which the commit will be performed. Specifically, you might want to rewrite the author/committer name/email/time environment variables (see git-commit(1) for details). Do not forget to re-export the variables.

--tree-filter <command>

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

--index-filter <command>

This is the filter for rewriting the index. It is similar to the tree filter but does not check out the tree, which makes it much faster. For hairy cases, see git-update-index(1).

--parent-filter <command>

This is the filter for rewriting the commit's parent list. It will receive the parent string on stdin and shall output the new parent string on stdout. The parent string is in a format accepted by git-commit-tree(1): empty for the initial commit, "-p parent" for a normal commit and "-p parent1 -p parent2 -p parent3 ..." for a merge commit.

--msg-filter <command>

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

--commit-filter <command>

This is the filter for performing the commit. If this filter is specified, it will be called instead of the git-commit-tree(1) command, with arguments of the form "<TREE_ID> [-p <PARENT_COMMIT_ID>]..." and the log message on stdin. The commit id is expected on stdout.

As a special extension, the commit filter may emit multiple commit ids; in that case, ancestors 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(1) instead).

--tag-name-filter <command>

This is the filter for rewriting tag names. When passed, it will be called for every tag ref that points to a rewritten object (or to a tag object which points to a rewritten object). The original tag name is passed via standard input, and the new tag 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 this case, be very careful and make sure you have the old tags backed up in case the conversion has run afoul.

Note that there is currently no support for proper rewriting of tag objects; in layman terms, if the tag has a message or signature attached, the rewritten tag won't have it. Sorry. (It is by definition impossible to preserve signatures at any rate.)

--subdirectory-filter <directory>

Only look at the history which touches the given subdirectory. The result will contain that directory (and only that) as its project root.

--original <namespace>

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

-d <directory>

Use this option to set the path to the temporary directory used for rewriting. When applying a tree filter, the command needs to temporary checkout the tree to some directory, which may consume considerable space in case of large projects. By default it does this in the .git-rewrite/ directory but you can override that choice by this parameter.

-f\|--force

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

<rev-list-options>

When options are given after the new branch name, they will be passed to git-rev-list(1). Only commits in the resulting output will be filtered, although the filtered commits can still reference parents which are outside of that set.
 

EXAMPLES

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


.ft C
git filter-branch --tree-filter 'rm filename' HEAD
.ft

A significantly faster version:


.ft C
git filter-branch --index-filter 'git update-index --remove filename' HEAD
.ft

Now, you will get the rewritten history saved in the branch newbranch (your current branch is left untouched).

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:


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

(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:


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

or even simpler:


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

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


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

The function skip_commits is defined as follows:


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

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.

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.

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(1).

Consider this history:


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

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


.ft C
git filter-branch ... C..H
.ft

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


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

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


.ft C
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
.ft

 

AUTHOR

Written by Petr "Pasky" Baudis <pasky@suse.cz>, and the git list <git@vger.kernel.org>  

DOCUMENTATION

Documentation by Petr Baudis and the git list.  

GIT

Part of the git(7) suite


 

Index

NAME
SYNOPSIS
DESCRIPTION
Filters
OPTIONS
EXAMPLES
AUTHOR
DOCUMENTATION
GIT




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