git-filter-branch - Online in the Cloud

PROGRAM:

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 <[email protected]>"
' 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 "$GIT_AUTHOR_EMAIL" = "root@localhost"
then
GIT_AUTHOR_EMAIL=[email protected]
export GIT_AUTHOR_EMAIL
fi
if test "$GIT_COMMITTER_EMAIL" = "root@localhost"
then
GIT_COMMITTER_EMAIL=[email protected]
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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