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GIT-FILTER-BRANCH(1)		  Git Manual		  GIT-FILTER-BRANCH(1)

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>]
	       [--prune-empty]
	       [--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 (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
       --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.

       --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".

       --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.

       <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:

       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
       warned.

       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).

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:

       o   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.

       o   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.

       o   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

Git 2.13.2			  06/24/2017		  GIT-FILTER-BRANCH(1)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXAMPLES | CHECKLIST FOR SHRINKING A REPOSITORY | NOTES | GIT | NOTES

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