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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). 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 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 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 the section called "Remap to ancestor".

   Remap to ancestor
       By using 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 is often 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).

GIT
       Part of the git(1) suite

Git 1.8.3.1				    06/10/2014			     GIT-FILTER-BRANCH(1)
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