Minor clarifications to git-filter-branch usage and doc

[thirdparty/git.git] / Documentation / git-filter-branch.txt

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>]
	[-d <directory>] [-f | --force] [<rev-list options>...]

DESCRIPTION
-----------
Lets you rewrite git revision history by creating a new branch from
your current branch, 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 takes the new branch name as a mandatory argument and
the filters as optional arguments.  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.

*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.

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 extensively I/O expensive, it might
be a good idea to redirect the temporary directory off-disk, 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 shell 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 set according to the current commit.

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 is the filter for modifying the environment in which
	the commit will be performed.  Specifically, you might want
	to rewrite the author/committer name/email/time environment
	variables (see gitlink:git-commit[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.  For hairy cases, see gitlink: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
	a format accepted by gitlink: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
	gitlink:git-commit-tree[1] 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, ancestors of the original commit will
have all of them as parents.

--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.
+
Note that there is currently no support for proper rewriting of
tag objects; in layman terms, if the tag has a message or signature
attached, the rewritten tag won't have it.  Sorry.  (It is by
definition impossible to preserve signatures at any rate.)

--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.

-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
	temporary checkout 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>::
	When options are given after the new branch name, they will
	be passed to gitlink:git-rev-list[1].  Only commits in the resulting
	output will be filtered, although the filtered commits can still
	reference parents which are outside of that set.


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
-------------------------------------------------------

A significantly faster version:

--------------------------------------------------------------------------
git filter-branch --index-filter 'git update-index --remove filename' HEAD
--------------------------------------------------------------------------

Now, you will get the rewritten history saved in the branch 'newbranch'
(your current branch is left untouched).

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 - therefore 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 \
	'cat; test $GIT_COMMIT = <commit-id> && echo "-p <graft-id>"' 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
		shift;
		while [ -n "$1" ];
		do
			shift;
			echo "$1";
			shift;
		done;
	else
		git commit-tree "$@";
	fi' HEAD
------------------------------------------------------------------------------

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.

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.

Note that the changes introduced by the commits, and 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 gitlink:git-rebase[1].

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
---------------------------------------------------------------


Author
------
Written by Petr "Pasky" Baudis <pasky@suse.cz>,
and the git list <git@vger.kernel.org>

Documentation
--------------
Documentation by Petr Baudis and the git list.

GIT
---
Part of the gitlink:git[7] suite