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GIT-FILTER-BRANCH(1) Git Manual GIT-FILTER-BRANCH(1)
git-filter-branch - Rewrite branches
git filter-branch [--setup <command>] [--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>...]
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.
--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.
--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.
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
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 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).
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:
· 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 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.
Part of the git(1) suite
1. The BFG Repo-Cleaner
http://rtyley.github.io/bfg-repo-cleaner/
2. command options
http://rtyley.github.io/bfg-repo-cleaner/#examples
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