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NAME | SYNOPSIS | WARNING | DESCRIPTION | OPTIONS | EXIT STATUS | EXAMPLES | CHECKLIST FOR SHRINKING A REPOSITORY | PERFORMANCE | SAFETY | GIT | NOTES | COLOPHON |
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GIT-FILTER-BRANCH(1) Git Manual GIT-FILTER-BRANCH(1)
git-filter-branch - Rewrite branches
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>...]
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.
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.
--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.
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.
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:
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 "$1";
shift;
done;
}
The shift magic first throws away the tree id and then the -p
parameters. Note that this handles merges properly! In case Darl
committed a merge between P1 and P2, it will be propagated
properly and all children of the merge will become merge commits
with P1,P2 as their parents instead of the merge commit.
NOTE the changes introduced by the commits, and which are not
reverted by subsequent commits, will still be in the rewritten
branch. If you want to throw out changes together with the
commits, you should use the interactive mode of git rebase.
You can rewrite the commit log messages using --msg-filter. For
example, git svn-id strings in a repository created by git svn
can be removed this way:
git filter-branch --msg-filter '
sed -e "/^git-svn-id:/d"
'
If you need to add Acked-by lines to, say, the last 10 commits
(none of which is a merge), use this command:
git filter-branch --msg-filter '
cat &&
echo "Acked-by: Bugs Bunny <[email protected]>"
' HEAD~10..HEAD
The --env-filter option can be used to modify committer and/or
author identity. For example, if you found out that your commits
have the wrong identity due to a misconfigured user.email, you
can make a correction, before publishing the project, like this:
git filter-branch --env-filter '
if test "$GIT_AUTHOR_EMAIL" = "root@localhost"
then
[email protected]
fi
if test "$GIT_COMMITTER_EMAIL" = "root@localhost"
then
[email protected]
fi
' -- --all
To restrict rewriting to only part of the history, specify a
revision range in addition to the new branch name. The new branch
name will point to the top-most revision that a git rev-list of
this range will print.
Consider this history:
D--E--F--G--H
/ /
A--B-----C
To rewrite only commits D,E,F,G,H, but leave A, B and C alone,
use:
git filter-branch ... C..H
To rewrite commits E,F,G,H, use one of these:
git filter-branch ... C..H --not D
git filter-branch ... D..H --not C
To move the whole tree into a subdirectory, or remove it from
there:
git filter-branch --index-filter \
'git ls-files -s | sed "s-\t\"*-&newsubdir/-" |
GIT_INDEX_FILE=$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:
• 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).
The performance of git-filter-branch is glacially slow; its
design makes it impossible for a backward-compatible
implementation to ever be fast:
• In editing files, git-filter-branch by design checks out each
and every commit as it existed in the original repo. If your
repo has 10^5 files and 10^5 commits, but each commit only
modifies five files, then git-filter-branch will make you do
10^10 modifications, despite only having (at most) 5*10^5
unique blobs.
• If you try and cheat and try to make git-filter-branch only
work on files modified in a commit, then two things happen
• you run into problems with deletions whenever the user is
simply trying to rename files (because attempting to
delete files that don’t exist looks like a no-op; it
takes some chicanery to remap deletes across file renames
when the renames happen via arbitrary user-provided
shell)
• even if you succeed at the map-deletes-for-renames
chicanery, you still technically violate backward
compatibility because users are allowed to filter files
in ways that depend upon topology of commits instead of
filtering solely based on file contents or names (though
this has not been observed in the wild).
• Even if you don’t need to edit files but only want to e.g.
rename or remove some and thus can avoid checking out each
file (i.e. you can use --index-filter), you still are passing
shell snippets for your filters. This means that for every
commit, you have to have a prepared git repo where those
filters can be run. That’s a significant setup.
• Further, several additional files are created or updated per
commit by git-filter-branch. Some of these are for supporting
the convenience functions provided by git-filter-branch (such
as map()), while others are for keeping track of internal
state (but could have also been accessed by user filters; one
of git-filter-branch’s regression tests does so). This
essentially amounts to using the filesystem as an IPC
mechanism between git-filter-branch and the user-provided
filters. Disks tend to be a slow IPC mechanism, and writing
these files also effectively represents a forced
synchronization point between separate processes that we hit
with every commit.
• The user-provided shell commands will likely involve a
pipeline of commands, resulting in the creation of many
processes per commit. Creating and running another process
takes a widely varying amount of time between operating
systems, but on any platform it is very slow relative to
invoking a function.
• git-filter-branch itself is written in shell, which is kind
of slow. This is the one performance issue that could be
backward-compatibly fixed, but compared to the above problems
that are intrinsic to the design of git-filter-branch, the
language of the tool itself is a relatively minor issue.
• Side note: Unfortunately, people tend to fixate on the
written-in-shell aspect and periodically ask if
git-filter-branch could be rewritten in another language
to fix the performance issues. Not only does that ignore
the bigger intrinsic problems with the design, it’d help
less than you’d expect: if git-filter-branch itself were
not shell, then the convenience functions (map(),
skip_commit(), etc) and the --setup argument could no
longer be executed once at the beginning of the program
but would instead need to be prepended to every user
filter (and thus re-executed with every commit).
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.
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:
• Someone can have a set of "working and tested filters" which
they document or provide to a coworker, who then runs them on
a different OS where the same commands are not working/tested
(some examples in the git-filter-branch manpage are also
affected by this). BSD vs. GNU userland differences can
really bite. If lucky, error messages are spewed. But just as
likely, the commands either don’t do the filtering requested,
or silently corrupt by making some unwanted change. The
unwanted change may only affect a few commits, so it’s not
necessarily obvious either. (The fact that problems won’t
necessarily be obvious means they are likely to go unnoticed
until the rewritten history is in use for quite a while, at
which point it’s really hard to justify another flag-day for
another rewrite.)
• Filenames with spaces are often mishandled by shell snippets
since they cause problems for shell pipelines. Not everyone
is familiar with find -print0, xargs -0, git-ls-files -z,
etc. Even people who are familiar with these may assume such
flags are not relevant because someone else renamed any such
files in their repo back before the person doing the
filtering joined the project. And often, even those familiar
with handling arguments with spaces may not do so just
because they aren’t in the mindset of thinking about
everything that could possibly go wrong.
• Non-ascii filenames can be silently removed despite being in
a desired directory. Keeping only wanted paths is often done
using pipelines like git ls-files | grep -v ^WANTED_DIR/ |
xargs git rm. ls-files will only quote filenames if needed,
so folks may not notice that one of the files didn’t match
the regex (at least not until it’s much too late). Yes,
someone who knows about core.quotePath can avoid this (unless
they have other special characters like \t, \n, or "), and
people who use ls-files -z with something other than grep can
avoid this, but that doesn’t mean they will.
• Similarly, when moving files around, one can find that
filenames with non-ascii or special characters end up in a
different directory, one that includes a double quote
character. (This is technically the same issue as above with
quoting, but perhaps an interesting different way that it can
and has manifested as a problem.)
• It’s far too easy to accidentally mix up old and new history.
It’s still possible with any tool, but git-filter-branch
almost invites it. If lucky, the only downside is users
getting frustrated that they don’t know how to shrink their
repo and remove the old stuff. If unlucky, they merge old and
new history and end up with multiple "copies" of each commit,
some of which have unwanted or sensitive files and others
which don’t. This comes about in multiple different ways:
• the default to only doing a partial history rewrite
(--all is not the default and few examples show it)
• the fact that there’s no automatic post-run cleanup
• the fact that --tag-name-filter (when used to rename
tags) doesn’t remove the old tags but just adds new ones
with the new name
• the fact that little educational information is provided
to inform users of the ramifications of a rewrite and how
to avoid mixing old and new history. For example, this
man page discusses how users need to understand that they
need to rebase their changes for all their branches on
top of new history (or delete and reclone), but that’s
only one of multiple concerns to consider. See the
"DISCUSSION" section of the git filter-repo manual page
for more details.
• Annotated tags can be accidentally converted to lightweight
tags, due to either of two issues:
• Someone can do a history rewrite, realize they messed up,
restore from the backups in refs/original/, and then redo
their git-filter-branch command. (The backup in
refs/original/ is not a real backup; it dereferences tags
first.)
• Running git-filter-branch with either --tags or --all in
your <rev-list-options>. In order to retain annotated
tags as annotated, you must use --tag-name-filter (and
must not have restored from refs/original/ in a
previously botched rewrite).
• Any commit messages that specify an encoding will become
corrupted by the rewrite; git-filter-branch ignores the
encoding, takes the original bytes, and feeds it to
commit-tree without telling it the proper encoding. (This
happens whether or not --msg-filter is used.)
• Commit messages (even if they are all UTF-8) by default
become corrupted due to not being updated — any references to
other commit hashes in commit messages will now refer to
no-longer-extant commits.
• There are no facilities for helping users find what unwanted
crud they should delete, which means they are much more
likely to have incomplete or partial cleanups that sometimes
result in confusion and people wasting time trying to
understand. (For example, folks tend to just look for big
files to delete instead of big directories or extensions, and
once they do so, then sometime later folks using the new
repository who are going through history will notice a build
artifact directory that has some files but not others, or a
cache of dependencies (node_modules or similar) which
couldn’t have ever been functional since it’s missing some
files.)
• If --prune-empty isn’t specified, then the filtering process
can create hoards of confusing empty commits
• If --prune-empty is specified, then intentionally placed
empty commits from before the filtering operation are also
pruned instead of just pruning commits that became empty due
to filtering rules.
• If --prune-empty is specified, sometimes empty commits are
missed and left around anyway (a somewhat rare bug, but it
happens...)
• A minor issue, but users who have a goal to update all names
and emails in a repository may be led to --env-filter which
will only update authors and committers, missing taggers.
• If the user provides a --tag-name-filter that maps multiple
tags to the same name, no warning or error is provided;
git-filter-branch simply overwrites each tag in some
undocumented pre-defined order resulting in only one tag at
the end. (A git-filter-branch regression test requires this
surprising behavior.)
Also, the poor performance of git-filter-branch often leads to
safety issues:
• Coming up with the correct shell snippet to do the filtering
you want is sometimes difficult unless you’re just doing a
trivial modification such as deleting a couple files.
Unfortunately, people often learn if the snippet is right or
wrong by trying it out, but the rightness or wrongness can
vary depending on special circumstances (spaces in filenames,
non-ascii filenames, funny author names or emails, invalid
timezones, presence of grafts or replace objects, etc.),
meaning they may have to wait a long time, hit an error, then
restart. The performance of git-filter-branch is so bad that
this cycle is painful, reducing the time available to
carefully re-check (to say nothing about what it does to the
patience of the person doing the rewrite even if they do
technically have more time available). This problem is extra
compounded because errors from broken filters may not be
shown for a long time and/or get lost in a sea of output.
Even worse, broken filters often just result in silent
incorrect rewrites.
• To top it all off, even when users finally find working
commands, they naturally want to share them. But they may be
unaware that their repo didn’t have some special cases that
someone else’s does. So, when someone else with a different
repository runs the same commands, they get hit by the
problems above. Or, the user just runs commands that really
were vetted for special cases, but they run it on a different
OS where it doesn’t work, as noted above.
Part of the git(1) suite
1. git filter-repo
https://github.com/newren/git-filter-repo/
2. filter-lamely
https://github.com/newren/git-filter-repo/blob/master/contrib/filter-repo-demos/filter-lamely
This page is part of the git (Git distributed version control
system) project. Information about the project can be found at
⟨http://git-scm.com/⟩. If you have a bug report for this manual
page, see ⟨http://git-scm.com/community⟩. This page was obtained
from the project's upstream Git repository
⟨https://github.com/git/git.git⟩ on 2024-06-14. (At that time,
the date of the most recent commit that was found in the
repository was 2024-06-12.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
Git 2.45.2.492.gd63586 2024-06-12 GIT-FILTER-BRANCH(1)
Pages that refer to this page: git(1)
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