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 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 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 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.
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
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