git-filter-branch manpage

Search topic Section


       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

       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

       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.

       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_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

       --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

       --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.

	   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 [ "$GIT_AUTHOR_NAME" = "Darl McBribe" ];
			   skip_commit "$@";
			   git commit-tree "$@";
		   fi' HEAD

       The function skip_commit is defined as follows:

		   while [ -n "$1" ];
			   map "$1";

       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 "$GIT_AUTHOR_EMAIL" = "root@localhost"
		   if test "$GIT_COMMITTER_EMAIL" = "root@localhost"
	   ' -- --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

       Consider this history:

	       /     /

       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 update-index --index-info &&

       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:

       o   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.

       o   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.

       o   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

       o   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.

       o   Expire all reflogs with git reflog expire --expire=now --all.

       o   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

       o   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.

       o   If you try and cheat and try to make git-filter-branch only work on
	   files modified in a commit, then two things happen

	   o   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)

	   o   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

       o   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.

       o   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.

       o   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.

       o   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.

	   o   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

       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

       o   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.)

       o   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.

       o   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.

       o   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

       o   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:

	   o   the default to only doing a partial history rewrite (--all is
	       not the default and few examples show it)

	   o   the fact that there's no automatic post-run cleanup

	   o   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

	   o   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.

       o   Annotated tags can be accidentally converted to lightweight tags,
	   due to either of two issues:

	   o   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.)

	   o   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).

       o   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

       o   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

       o   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.)

       o   If --prune-empty isn't specified, then the filtering process can
	   create hoards of confusing empty commits

       o   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.

       o   If --prune-empty is specified, sometimes empty commits are missed
	   and left around anyway (a somewhat rare bug, but it happens...)

       o   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.

       o   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

       o   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.

       o   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

	2. filter-lamely

Git 2.38.4			  05/16/2024		  GIT-FILTER-BRANCH(1)