Documentation/git-filter-branch.txt - git - Git at Google

 git-filter-branch(1)
 ====================

 NAME
 ----
 git-filter-branch - Rewrite branches

 SYNOPSIS
 --------
 [verse]
 '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 linkgit: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 linkgit: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 linkgit:git-commit-tree[1] for details).  Do not forget
 	to re-export the variables.

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

 --index-filter <command>::
 	This is the filter for rewriting the index.  It is similar to the
 	tree filter but does not check out the tree, which makes it much
 	faster.  Frequently used with `git rm --cached
 	--ignore-unmatch ...`, see EXAMPLES below.  For hairy
 	cases, see linkgit: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 linkgit: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 <<Remap_to_ancestor>>.

 --prune-empty::
 	Some kind of filters will generate empty commits, that left the tree
 	untouched.  This switch allow git-filter-branch to ignore such
 	commits.  Though, this switch only applies for commits that have one
 	and only one parent, it will hence keep merges points. Also, this
 	option is not compatible with the use of `--commit-filter`. Though you
 	just need to use the function 'git_commit_non_empty_tree "$@"' instead
 	of the `git commit-tree "$@"` idiom in your commit filter to make that
 	happen.

 --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 <<Remap_to_ancestor>>.


 [[Remap_to_ancestor]]
 Remap to ancestor
 ~~~~~~~~~~~~~~~~~

 By using linkgit: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 "$GIT_AUTHOR_EMAIL" = "root@localhost"
 	then
 		GIT_AUTHOR_EMAIL=john@example.com
 		export GIT_AUTHOR_EMAIL
 	fi
 	if test "$GIT_COMMITTER_EMAIL" = "root@localhost"
 	then
 		GIT_COMMITTER_EMAIL=john@example.com
 		export GIT_COMMITTER_EMAIL
 	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 linkgit: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
 http://rtyley.github.io/bfg-repo-cleaner/[The BFG Repo-Cleaner],
 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 http://rtyley.github.io/bfg-repo-cleaner/#examples[command options]
   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 linkgit:git[1] suite
	git-filter-branch(1)
	====================

	NAME
	----
	git-filter-branch - Rewrite branches

	SYNOPSIS
	--------
	[verse]
	'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 linkgit: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 linkgit: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 linkgit:git-commit-tree[1] for details). Do not forget
	to re-export the variables.

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

	--index-filter <command>::
	This is the filter for rewriting the index. It is similar to the
	tree filter but does not check out the tree, which makes it much
	faster. Frequently used with `git rm --cached
	--ignore-unmatch ...`, see EXAMPLES below. For hairy
	cases, see linkgit: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 linkgit: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 <<Remap_to_ancestor>>.

	--prune-empty::
	Some kind of filters will generate empty commits, that left the tree
	untouched. This switch allow git-filter-branch to ignore such
	commits. Though, this switch only applies for commits that have one
	and only one parent, it will hence keep merges points. Also, this
	option is not compatible with the use of `--commit-filter`. Though you
	just need to use the function 'git_commit_non_empty_tree "$@"' instead
	of the `git commit-tree "$@"` idiom in your commit filter to make that
	happen.

	--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 <<Remap_to_ancestor>>.


	[[Remap_to_ancestor]]
	Remap to ancestor
	~~~~~~~~~~~~~~~~~

	By using linkgit: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 "$GIT_AUTHOR_EMAIL" = "root@localhost"
	then
	GIT_AUTHOR_EMAIL=john@example.com
	export GIT_AUTHOR_EMAIL
	fi
	if test "$GIT_COMMITTER_EMAIL" = "root@localhost"
	then
	GIT_COMMITTER_EMAIL=john@example.com
	export GIT_COMMITTER_EMAIL
	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 linkgit: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
	http://rtyley.github.io/bfg-repo-cleaner/[The BFG Repo-Cleaner],
	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 http://rtyley.github.io/bfg-repo-cleaner/#examples[command options]
	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 linkgit:git[1] suite