Provided by: git-man_2.17.1-1ubuntu0.18_all 
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 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>
This is not a real filter executed for each commit but a one time setup just before the loop.
Therefore no commit-specific variables are defined yet. Functions or variables defined here can be
used or modified in the following filter steps except the commit filter, for technical reasons.
--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. Implies the section called “Remap to ancestor”.
--env-filter <command>
This filter may be used if you only need to modify 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-tree(1) for details).
--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. Frequently used with git rm --cached --ignore-unmatch ..., see
EXAMPLES below. 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 the format described in
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 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, 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>
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.
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
Some filters will generate empty commits that leave the tree untouched. This option instructs
git-filter-branch to remove such commits if they have exactly one or zero non-pruned parents; merge
commits will therefore remain intact. This option cannot be used together with --commit-filter,
though the same effect can be achieved by using the provided git_commit_non_empty_tree function in a
commit filter.
--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 temporarily check out 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.
--state-branch <branch>
This option will cause the mapping from old to new objects to be loaded from named branch upon
startup and saved as a new commit to that branch upon exit, enabling incremental of large trees. If
<branch> does not exist it will be created.
<rev-list options>...
Arguments for git rev-list. All positive refs included by these options are rewritten. You may also
specify options such as --all, but you must use -- to separate them from the git filter-branch
options. Implies the section called “Remap to ancestor”.
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.
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 \
'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 "$1";
shift;
done;
}
The shift magic first throws away the tree id and then the -p parameters. Note that this handles merges
properly! In case Darl committed a merge between P1 and P2, it will be propagated properly and all
children of the merge will become merge commits with P1,P2 as their parents instead of the merge commit.
NOTE the changes introduced by the commits, and which are not reverted by subsequent commits, will still
be in the rewritten branch. If you want to throw out changes together with the commits, you should use
the interactive mode of git rebase.
You can rewrite the commit log messages using --msg-filter. For example, git svn-id strings in a
repository created by git svn can be removed this way:
git filter-branch --msg-filter '
sed -e "/^git-svn-id:/d"
'
If you need to add Acked-by lines to, say, the last 10 commits (none of which is a merge), use this
command:
git filter-branch --msg-filter '
cat &&
echo "Acked-by: Bugs Bunny <bunny@bugzilla.org>"
' HEAD~10..HEAD
The --env-filter option can be used to modify committer and/or author identity. For example, if you found
out that your commits have the wrong identity due to a misconfigured user.email, you can make a
correction, before publishing the project, like this:
git filter-branch --env-filter '
if test "$GIT_AUTHOR_EMAIL" = "root@localhost"
then
GIT_AUTHOR_EMAIL=john@example.com
fi
if test "$GIT_COMMITTER_EMAIL" = "root@localhost"
then
GIT_COMMITTER_EMAIL=john@example.com
fi
' -- --all
To restrict rewriting to only part of the history, specify a revision range in addition to the new branch
name. The new branch name will point to the top-most revision that a git rev-list of this range will
print.
Consider this history:
D--E--F--G--H
/ /
A--B-----C
To rewrite only commits D,E,F,G,H, but leave A, B and C alone, use:
git filter-branch ... C..H
To rewrite commits E,F,G,H, use one of these:
git filter-branch ... C..H --not D
git filter-branch ... D..H --not C
To move the whole tree into a subdirectory, or remove it from there:
git filter-branch --index-filter \
'git ls-files -s | sed "s-\t\"*-&newsubdir/-" |
GIT_INDEX_FILE=$GIT_INDEX_FILE.new \
git update-index --index-info &&
mv "$GIT_INDEX_FILE.new" "$GIT_INDEX_FILE"' HEAD
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:
• You really removed all variants of a filename, if a blob was moved over its lifetime. git log
--name-only --follow --all -- filename can help you find renames.
• You really filtered all refs: use --tag-name-filter cat -- --all when calling git-filter-branch.
Then there are two ways to get a smaller repository. A safer way is to clone, that keeps your original
intact.
• Clone it with git clone file:///path/to/repo. The clone will not have the removed objects. See git-
clone(1). (Note that cloning with a plain path just hardlinks everything!)
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.
• Remove the original refs backed up by git-filter-branch: say git for-each-ref --format="%(refname)"
refs/original/ | xargs -n 1 git update-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 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[1], a JVM-based alternative
to git-filter-branch, typically at least 10-50x faster for those use-cases, and with quite different
characteristics:
• Any particular version of a file is cleaned exactly once. The BFG, unlike git-filter-branch, does not
give you the opportunity to handle a file differently based on where or when it was committed within
your history. This constraint gives the core performance benefit of The BFG, and is well-suited to
the task of cleansing bad data - you don’t care where the bad data is, you just want it gone.
• By default The BFG takes full advantage of multi-core machines, cleansing commit file-trees in
parallel. git-filter-branch cleans commits sequentially (i.e. in a single-threaded manner), though it
is possible to write filters that include their own parallelism, in the scripts executed against each
commit.
• The command options[2] are much more restrictive than git-filter branch, and dedicated just to the
tasks of removing unwanted data- e.g: --strip-blobs-bigger-than 1M.
GIT
Part of the git(1) suite
NOTES
1. The BFG Repo-Cleaner
http://rtyley.github.io/bfg-repo-cleaner/
2. command options
http://rtyley.github.io/bfg-repo-cleaner/#examples