git-filter-repo.txt

git-filter-repo(1)
==================

NAME
----
git-filter-repo - Rewrite repository history

SYNOPSIS
--------
[verse]
'git filter-repo' --analyze
'git filter-repo' [<path_filtering_options>] [<content_filtering_options>]
	[<ref_renaming_options>] [<commit_message_filtering_options>]
	[<name_or_email_filtering_options>] [<parent_rewriting_options>]
	[<generic_callback_options>] [<miscellaneous_options>]

DESCRIPTION
-----------

Rapidly rewrite entire repository history using user-specified filters.
This is a destructive operation which should not be used lightly; it
writes new commits, trees, tags, and blobs corresponding to (but
filtered from) the original objects in the repository, then deletes the
original history and leaves only the new.  See <<DISCUSSION>> for more
details on the ramifications of using this tool.  Several different
types of history rewrites are possible; examples include (but are not
limited to):

  * stripping large files (or large directories or large extensions)
  * stripping unwanted files by path
  * extracting wanted paths and their history (stripping everything else)
  * restructuring the file layout (such as moving all files into a
    subdirectory in preparation for merging with another repo, making a
    subdirectory become the new toplevel directory, or merging two
    directories with independent filenames into one directory)
  * renaming tags (also often in preparation for merging with another repo)
  * replacing or removing sensitive text such as passwords
  * making mailmap rewriting of user names or emails permanent
  * making grafts or replacement refs permanent
  * rewriting commit messages

Additionally, several concerns are handled automatically (many of these
can be overridden, but they are all on by default):

  * rewriting (possibly abbreviated) hashes in commit messages to
    refer to the new post-rewrite commit hashes
  * pruning commits which become empty due to the above filters (also
    handles edge cases like pruning of merge commits which become
    degenerate and empty)
  * creating replace-refs (see linkgit:git-replace[1]) for old commit
    hashes, which if pushed and fetched will allow users to continue to
    refer to new commits using (unabbreviated) old commit IDs
  * stripping of original history to avoid mixing old and new history
  * repacking the repository post-rewrite to shrink the repo for the
    user

Also, it's worth noting that there is an important safety mechanism:

  * abort if run from a repo that is not a fresh clone (to prevent
    accidental data loss from rewriting local history that doesn't
    exist anywhere else)

For those who know that there is large unwanted stuff in their history
and want help finding it, this command also

  * provides an option to analyze a repository and generate reports that
    can be useful in determining what to filter (or in determining
    whether a separate filtering command was successful).

See also <<VERSATILITY>>, <<DISCUSSION>>, <<EXAMPLES>>, and
<<INTERNALS>>.

OPTIONS
-------

Analysis Options
~~~~~~~~~~~~~~~~

--analyze::
	Analyze repository history and create a report that may be
	useful in determining what to filter in a subsequent run (or
	in determining if a previous filtering command did what you
	wanted).  Will not modify your repo.

Filtering based on paths (see also --filename-callback)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

--invert-paths::
	Invert the selection of files from the specified
	--path-{match,glob,regex} options below, i.e. only select
	files matching none of those options.

--path-match <dir_or_file>::
--path <dir_or_file>::
	Exact paths (files or directories) to include in filtered
	history.  Multiple --path options can be specified to get a
	union of paths.

--path-glob <glob>::
	Glob of paths to include in filtered history.  Multiple
	--path-glob options can be specified to get a union of paths.

--path-regex <regex>::
	Regex of paths to include in filtered history.  Multiple
	--path-regex options can be specified to get a union of paths.

--use-base-name::
	Match on file base name instead of full path from the top of
	the repo.  Incompatible with --path-rename.

Renaming based on paths (see also --filename-callback)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

--path-rename <old_name:new_name>::
--path-rename-match <old_name:new_name>::
	Path to rename; if filename or directory matches <old_name>
	rename to <new_name>.  Multiple --path-rename options can be
	specified.

Path shortcuts
~~~~~~~~~~~~~~

--paths-from-file <filename>::
	Specify several path filtering and renaming directives, one
	per line. Lines with `==>` in them specify path renames, and
	lines can begin with `literal:` (the default), `glob:`, or
	`regex:` to specify different matching styles

--subdirectory-filter <directory>::
	Only look at history that touches the given subdirectory and
	treat that directory as the project root. Equivalent to using
	`--path <directory>/ --path-rename <directory>/:`

--to-subdirectory-filter <directory>::
	Treat the project root as instead being under
	<directory>.  Equivalent to using `--path-rename :<directory>/`

Content editing filters (see also --blob-callback)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

--replace-text <expressions_file>::
	A file with expressions that, if found, will be replaced. By
	default, each expression is treated as literal text, but
	`regex:` and `glob:` prefixes are supported. You can end the
	line with `==>` and some replacement text to choose a
	replacement choice other than the default of `***REMOVED***`.

--strip-blobs-bigger-than <size>::
	Strip blobs (files) bigger than specified size (e.g. `5M`,
	`2G`, etc)

--strip-blobs-with-ids <blob_id_filename>::
	Read git object ids from each line of the given file, and
	strip all of them from history

Renaming of refs (see also --refname-callback)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

--tag-rename <old:new>::
	Rename tags starting with <old> to start with <new>. For example,
	--tag-rename foo:bar will rename tag foo-1.2.3 to bar-1.2.3;
	either <old> or <new> can be empty.

Filtering of commit messages (see also --message-callback)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

--preserve-commit-hashes::
	By default, since commits are rewritten and thus gain new
	hashes, references to old commit hashes in commit messages are
	replaced with new commit hashes (abbreviated to the same
	length as the old reference).  Use this flag to turn off
	updating commit hashes in commit messages.

--preserve-commit-encoding::
	Do not reencode commit messages into UTF-8. By default, if the
	commit object specifies an encoding for the commit message,
	the message is re-encoded into UTF-8.

Filtering of names & emails (see also --name-callback and --email-callback)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

--mailmap <filename>::
	Use specified mailmap file (see linkgit:git-shortlog[1] for details
	on the format) when rewriting author, committer, and tagger names
	and emails. If the specified file is part of git history,
	historical versions of the file will be ignored; only the current
	contents are consulted.

--use-mailmap::
	Same as: '--mailmap .mailmap'

Parent rewriting
~~~~~~~~~~~~~~~~

--replace-refs {delete-no-add, delete-and-add, update-no-add, update-or-add, update-and-add}::
	Replace refs (see linkgit:git-replace[1]) are used to rewrite
	parents (unless turned off by the usual git mechanism); this
	flag specifies what do do with those refs afterward. Replace
	refs can either be deleted or updated to point at new commit
	hashes. Also, new replace refs can be added for each commit
	rewrite.  With 'update-or-add', new replace refs are only
	added for commit rewrites that aren't used to update an
	existing replace ref. default is 'update-and-add' if
	$GIT_DIR/filter-repo/already_ran does not exist;
	'update-or-add' otherwise.

--prune-empty {always, auto, never}::
	Whether to prune empty commits. 'auto' (the default) means
	only prune commits which become empty (not commits which were
	empty in the original repo, unless their parent was
	pruned). When the parent of a commit is pruned, the first
	non-pruned ancestor becomes the new parent.

--prune-degenerate {always, auto, never}::
	Since merge commits are needed for history topology, they are
	typically exempt from pruning. However, they can become
	degenerate with the pruning of other commits (having fewer
	than two parents, having one commit serve as both parents, or
	having one parent as the ancestor of the other.) If such merge
	commits have no file changes, they can be pruned. The default
	('auto') is to only prune empty merge commits which become
	degenerate (not which started as such).

Generic callback code snippets
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

--filename-callback <function_body>::
	Python code body for processing filenames; see <<CALLBACKS>>.

--message-callback <function_body>::
	Python code body for processing messages (both commit messages and
	tag messages); see <<CALLBACKS>>.

--name-callback <function_body>::
	Python code body for processing names of people; see <<CALLBACKS>>.

--email-callback <function_body>::
	Python code body for processing emails addresses; see
	<<CALLBACKS>>.

--refname-callback <function_body>::
	Python code body for processing refnames; see <<CALLBACKS>>.

--blob-callback <function_body>::
	Python code body for processing blob objects; see <<CALLBACKS>>.

--commit-callback <function_body>::
	Python code body for processing commit objects; see <<CALLBACKS>>.

--tag-callback <function_body>::
	Python code body for processing tag objects; see <<CALLBACKS>>.

--reset-callback <function_body>::
	Python code body for processing reset objects; see <<CALLBACKS>>.

Location to filter from/to
~~~~~~~~~~~~~~~~~~~~~~~~~~

NOTE: Specifying alternate source or target locations implies --partial
except that the normal default for --replace-refs is used.  However, unlike
normal uses of --partial, this doesn't risk mixing old and new history
since the old and new histories are in different repositories.

--source <source>::
	Git repository to read from

--target <target>::
	Git repository to overwrite with filtered history

Miscellaneous options
~~~~~~~~~~~~~~~~~~~~~

--help::
-h::
	Show a help message and exit.

--force::
-f::
	Rewrite history even if the current repo does not look like a fresh
	clone.

--partial::
	Do a partial history rewrite, resulting in the mixture of old and
	new history.  This implies a default of update-no-add for
	--replace-refs, disables rewriting refs/remotes/origin/* to
	refs/heads/*, disables removing of the 'origin' remote, disables
	removing unexported refs, disables expiring the reflog, and
	disables the automatic post-filter gc.  Also, this modifies
	--tag-rename and --refname-callback options such that instead of
	replacing old refs with new refnames, it will instead create new
	refs and keep the old ones around.  Use with caution.

--refs <refs+>::
	Limit history rewriting to the specified refs.  Implies --partial.
        In addition to the normal caveats of --partial (mixing old and new
        history, no automatic remapping of refs/remotes/origin/* to
        refs/heads/*, etc.), this also may cause problems for pruning of
        degenerate empty merge commits when negative revisions are
        specified.

--dry-run::
	Do not change the repository. Run `git fast-export` and filter its
	output, and save both the original and the filtered version for
	comparison.  This also disables rewriting commit messages due to
	not knowing new commit IDs and disables filtering of some empty
	commits due to inability to query the fast-import backend.

--debug::
	Print additional information about operations being performed and
	commands being run.  (If used together with --dry-run, shows
	extra information about what would be run).

--stdin::
	Instead of running `git fast-export` and filtering its output,
	filter the fast-export stream from stdin.  The stdin must be in
	the expected input format (e.g. it needs to include original-oid
	directives).

--quiet::
	Pass --quiet to other git commands called.

[[VERSATILITY]]
VERSATILITY
-----------

filter-repo has a hierarchy of capabilities on the spectrum from easy to
use convenience flags that perform pre-defined types of filtering, to
choices that provide lots of flexibility in controlling how filtering
occurs.  This spectrum includes the following:

  * Convenience flags making common types of history rewriting simple (e.g.
    --path, --strip-blobs-bigger-than, --replace-text, --mailmap)
  * Options which are shorthand for others or which provide greater control
    than others (e.g. --subdirectory-filter could just be written using
    both a path selection (--path) and a path rename (--path-rename)
    filter; --paths-from-file can handle all other --path* options and more
    such as regex renaming of paths)
  * Generic python callbacks for handling a certain type of data (the
    filename, message, name, email, and refname callbacks)
  * Generic python callbacks for handling fundamental git objects, allowing
    greater control over the combination of data types the object holds
    (the commit, tag, blob, and reset callbacks)
  * The ability to import filter-repo as a module in a python program and
    use its classes and functions for even greater control and flexibility
    while still leveraging lots of basic capabilities.  One can even use
    this to write new tools with a completely different interface.

For more information about callbacks, see <<CALLBACKS>>.  For examples on
writing python programs that import filter-repo as a module to create new
history rewriting tools, look at the contrib/filter-repo-demos/ directory.
That directory includes, among other examples, a reimplementation of
git-filter-branch which is faster than git-filter-branch, and a
reimplementation of BFG Repo Cleaner with several bug fixes and new
features.

[[DISCUSSION]]
DISCUSSION
----------

Using filter-repo is relatively simple, but rewriting history is part of
a larger discussion in terms of collaboration.  When you rewrite
history, the old and new histories are no longer compatible; if you push
this history somewhere for others to view, it will look as though you've
done a rebase of all branches and tags.  Make sure you are familiar with
the "RECOVERING FROM UPSTREAM REBASE" section of linkgit:git-rebase[1]
(and in particular, "The hard case") before proceeding, in addition to
this section.

Steps to use git-filter-repo as part of the bigger picture of doing a
history rewrite are roughly as follows:

1. Create a clone of your repository (if you created special refs outside
   of refs/heads/ or refs/tags/, make sure to fetch those too).  Note
   that `--bare` and `--mirror` clones are supported too, if you prefer.

2. (Optional) Run `git filter-repo --analyze`.  This will create a
   directory of reports mentioning renames that have occurred in your
   repo and also listing sizes of objects aggregated by
   path/directory/extension/blob-id; this information may be useful in
   choosing how to filter your repo.  It can also be useful to re-run
   --analyze after filtering to verify the changes look correct.

3. Run filter-repo with your desired filtering options.  Many examples
   are given below.  For more complex cases, note that doing the
   filtering in multiple steps (by running multiple filter-repo
   invocations in a sequence) is supported.  If anything goes wrong here,
   simply delete your clone and restart.

4. Push your new repository to its new home (note that
   refs/remotes/origin/* will have been moved to refs/heads/* as the
   first part of filter-repo, so you can just deal with normal branches
   instead of remote tracking branches).  While you can force push this
   to the same URL you cloned from, there are good reasons to consider
   pushing to a different location instead:

   * People who cloned from the original repo will have old history.
     When they fetch the new history you force pushed up, unless they
     do a `git reset --hard @{u}` on their branches or rebase their
     local work, git will think they have hundreds or thousands of
     commits with very similar commit messages as what exist upstream
     (but which include files you wanted excised from history), and
     allow the user to merge the two histories, resulting in what
     looks like two copies of each commit.  If they then push this
     history back up, then everyone now has history with two copies of
     each commit and the bad files have returned.  You're more likely
     to succeed in forcing people to get rid of the old history if
     they have to clone a new URL.

   * Rewriting history will rewrite tags; those who have already
     downloaded tags will not get the updated tags by default (see the
     "On Re-tagging" section of linkgit:git-tag[1]).  Every user
     trying to use an existing clone will have to forcibly delete all
     tags and re-fetch them; it may be easier for them to just
     re-clone, which they are more likely to do with a new clone URL.

   * Rewriting history may delete some refs (e.g. branches that only
     had files that you wanted excised from history); unless you run
     git push with the `--mirror` or `--prune` options, those refs
     will continue to exist on the server.  If folks then merge these
     branches into others, then people have started mixing old and new
     history.  If users had already cloned these branches, removing
     them from the server isn't enough; you need all users to delete
     any local branches based on these refs and run fetch with the
     `--prune` option as well.  Simply re-cloning from a new URL is
     easier.

   * The server may not allow you to force push over some refs.
     For example, code review systems may have special ref
     namespaces (e.g. refs/changes/, refs/pull/,
     refs/merge-requests/) that they have locked down.

5. (Optional) Some additional considerations

   * filter-repo by default creates replace refs (see
     linkgit:git-replace[1]) for each rewritten commit ID, allowing
     you to use old (unabbreviated) commit hashes to refer to the
     newly rewritten commits.  If you want to use these replace refs,
     push them to the relevant clone URL and tell users to adjust
     their fetch refspec (e.g. `git config --add remote.origin.fetch
     +refs/replace/*:refs/replace/*`) Sadly, some existing git servers
     (e.g. Gerrit, GitHub) do not yet understand replace refs, and
     thus one can't use old commit hashes within their UI; this may
     change in the future.  But replace refs at least help users
     locally within the git CLI.

   * If you have a central repo, you may want to prevent people
     from pushing old commit IDs, in order to avoid mixing old
     and new history.  Every repository manager does this
     differently, some provide specialized commands
     (e.g. https://gerrit-review.googlesource.com/Documentation/cmd-ban-commit.html),
     others require you to write hooks.

[[EXAMPLES]]
EXAMPLES
--------

Path based filtering
~~~~~~~~~~~~~~~~~~~~

To only keep the 'README.md' file plus the directories 'guides' and
'tools/releases/':

--------------------------------------------------
git filter-repo --path README.md --path guides/ --path tools/releases
--------------------------------------------------

Directory names can be given with or without a trailing slash, and all
filenames are relative to the toplevel of the repo.  To keep all files
except these paths, just add `--invert-paths`:

--------------------------------------------------
git filter-repo --path README.md --path guides/ --path tools/releases --invert-paths
--------------------------------------------------

If you want to have both an inclusion filter and an exclusion filter, just
run filter-repo multiple times.  For example, to keep the src/main
subdirectory but exclude files under src/main named 'data', run:

--------------------------------------------------
git filter-repo --path src/main/
git filter-repo --path-glob 'src/*/data' --invert-paths
--------------------------------------------------

Note that the asterisk (`*`) will match across multiple directories, so the
second command would remove e.g. src/main/org/whatever/data.  Also, the
second command by itself would also remove e.g. src/not-main/foo/data, but
since src/not-main/ was removed by the first command, that's not an issue.
Also, the use of quotes around the asterisk is sometimes important to avoid
glob expansion by the shell.

You can also select paths by regular expression (see
https://docs.python.org/3/library/re.html#regular-expression-syntax).
For example, to only include files from the repo whose name is in the
format YYYY-MM-DD.txt and is found at least two subdirectories deep:

--------------------------------------------------
git filter-repo --path-regex '^.*/.*/[0-9]{4}-[0-9]{2}-[0-9]{2}.txt$'
--------------------------------------------------

If you want two directories to be renamed (and maybe merged if both are
renamed to the same location), use --path-rename; for example, to rename
both 'cmds/' and 'src/scripts/' to 'tools/':

--------------------------------------------------
git filter-repo --path-rename cmds:tools --path-rename src/scripts/:tools/
--------------------------------------------------

As with `--path`, directories can be specified with or without a
trailing slash for `--path-rename`.

If you do a `--path-rename` to something that was already in use, it will
be silently overwritten.  However, if you try to rename multiple files to
the same location (e.g. src/scripts/run_release.sh and cmds/run_release.sh
both existed and had different content with the renames above), then you
will be given an error.  If you have such a case, you may want to add
another rename command to move one of the paths somewhere else where it
won't collide:

--------------------------------------------------
git filter-repo --path-rename cmds/run_release.sh:tools/do_release.sh \
                --path-rename cmds/:tools/ \
                --path-rename src/scripts/:tools/
--------------------------------------------------

Also, `--path-rename` brings up ordering issues; all path arguments are
applied in order.  Thus, a command like

--------------------------------------------------
git filter-repo --path-rename sources/:src/main/ --path src/main/
--------------------------------------------------

would make sense but reversing the two arguments would not (src/main/ is
created by the rename so reversing the two would give you an empty repo).
Also, note that the rename of cmds/run_release.sh a couple examples ago was
done before the other renames.

If you prefer to filter based solely on basename, use the `--use-base-name`
flag (though this is incompatible with `--path-rename`).  For example, to
only include README.md and Makefile files from any directory:

--------------------------------------------------
git filter-repo --use-base-name --path README.md --path Makefile
--------------------------------------------------

If you wanted to delete all .DS_Store files in any directory, you could
either use:

--------------------------------------------------
git filter-repo --invert-paths --path '.DS_Store' --use-base-name
--------------------------------------------------

or

--------------------------------------------------
git filter-repo --invert-paths --path-glob '*/.DS_Store' --path '.DS_Store'
--------------------------------------------------

(the `--path-glob` isn't sufficient by itself as it might miss a toplevel
.DS_Store file; further while something like `--path-glob '*.DS_Store'`
would workaround that problem it would also grab files named `foo.DS_Store`
or `bar/baz.DS_Store`)

If you have a long list of files, directories, globs, or regular
expressions to filter on, you can stick them in a file and use
`--paths-from-file`; for example, with a file named stuff-i-want.txt with
contents of

--------------------------------------------------
README.md
guides/
tools/releases
glob:*.py
regex:^.*/.*/[0-9]{4}-[0-9]{2}-[0-9]{2}.txt$
tools/==>scripts/
regex:(.*)/([^/]*)/([^/]*)\.text$==>\2/\1/\3.txt
--------------------------------------------------

then you could run

--------------------------------------------------
git filter-repo --paths-from-file stuff-i-want.txt
--------------------------------------------------

to get a repo containing only the toplevel README.md file, the guides/ and
tools/releases/ directories, all python files, files whose name was of the
form YYYY.MM-DD.txt at least two subdirectories deep, and would rename
tools/ to scripts/ and rename files like foo/bar/baz/bleh.text to
baz/foo/bar/bleh.txt.  Note the special line prefixes of `glob:` and
`regex:` and the special string `==>` denoting renames.

Finally, see also the `--filename-callback` from <<CALLBACKS>>.

Content based filtering
~~~~~~~~~~~~~~~~~~~~~~~

If you want to filter out all files bigger than a certain size, you can use
`--strip-blobs-bigger-than` with some size (K, M, and G suffixes are
recognized), e.g.:

--------------------------------------------------
git filter-repo --strip-blobs-bigger-than 10M
--------------------------------------------------

If you want to strip out all files with specified git object ids (hashes),
list the hashes in a file and run

--------------------------------------------------
git filter-repo --strip-blobs-with-ids FILE_WITH_GIT_BLOB_IDS
--------------------------------------------------

If you want to modify file contents, you can do so based on a list of
expressions in a file, one per line.  For example, with a file named
expressions.txt containing

--------------------------------------------------
p455w0rd
foo==>bar
glob:*666*==>
regex:\bdriver\b==>pilot
literal:MM/DD/YYYY=>YYYY-MM-DD
regex:([0-9]{2})/([0-9]{2})/([0-9]{4})==>\3-\1-\2
--------------------------------------------------

then running
--------------------------------------------------
git filter-repo --replace-text expressions.txt
--------------------------------------------------

will go through and replace `p455w0rd` with `***REMOVED***`, `foo` with
`bar`, any line containing `666` with a blank line, the word `driver` with
`pilot` (but not if it has letters before or after; e.g. `drivers` will be
unmodified), replace the exact text `MM/DD/YYYY` with `YYYY-MM-DD` and
replace date strings of the form MM/DD/YYYY with ones of the form
YYYY-MM-DD.  In the expressions file, there are a few things to note:

  * Every line has a replacement, given by whatever is on the right of
    `==>`.  If `==>` does not appear on the line, the default replacement
    is `***REMOVED***`.
  * Lines can start with `literal:`, `glob:`, or `regex:` to specify
    whether to do literal string matches,
    globs (see https://docs.python.org/3/library/fnmatch.html), or regular
    expressions (see https://docs.python.org/3/library/re.html#regular-expression-syntax).
    If none of these are specified, `literal:` is assumed.
  * globs and regexes are applied to each line of the file; it is not
    possible with --replace-text to match a multi-line string.
  * If multiple matches are found on a line, all are replaced.

See also the `--blob-callback` from <<CALLBACKS>>.

Refname based filtering
~~~~~~~~~~~~~~~~~~~~~~~

To rename tags, use `--tag-rename`, e.g.:

--------------------------------------------------
git filter-repo --tag-rename foo:bar
--------------------------------------------------

This will rename any tags starting with `foo` to now start with `bar`.
Either side of the colon could be blank, e.g.

--------------------------------------------------
git filter-repo --tag-rename '':'my-module-'
--------------------------------------------------

For more general refname modification, see `--refname-callback` from
<<CALLBACKS>>.

User and email based filtering
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To modify username and emails of commits, you can create a mailmap
file in the format accepted by linkgit:git-shortlog[1].  For example,
if you have a file named my-mailmap you can run

--------------------------------------------------
git filter-repo --mailmap my-mailmap
--------------------------------------------------

and if the current contents of that file are as follows (if the
specified mailmap file is version controlled, historical versions of
the file are ignored):

--------------------------------------------------
Name For User <email@addre.ss>
<new@ema.il> <old1@ema.il>
New Name And <new@ema.il> <old2@ema.il>
New Name And <new@ema.il> Old Name And <old3@ema.il>
--------------------------------------------------

then we can update username and/or emails based on the specified
mapping.

See also the `--name-callback` and `--email-callback` from
<<CALLBACKS>>.

Parent rewriting
~~~~~~~~~~~~~~~~

To replace $commit_A with $commit_B (e.g. make all commits which had
$commit_A as a parent instead have $commit_B for that parent), and
rewrite history to make it permanent:

--------------------------------------------------
git replace $commit_A $commit_B
git filter-repo --force
--------------------------------------------------

To create a new commit with the same contents as $commit_A except with
different parent(s) and then replace $commit_A with the new commit,
and rewrite history to make it permanent:

--------------------------------------------------
git replace --graft $commit_A $new_parent_or_parents
git filter-repo --force
--------------------------------------------------

The reason to specify --force is two-fold: filter-repo will error out
if no arguments are specified, and the new graft commit would
otherwise trigger the not-a-fresh-clone check.

Partial history rewrites
~~~~~~~~~~~~~~~~~~~~~~~~

To rewrite the history on just one branch (which may cause it to no longer
share any common history with other branches), use `--refs`.  For example,
to remove a file named 'extraneous.txt' from the 'master' branch:

--------------------------------------------------
git filter-repo --invert-paths --path extraneous.txt --refs master
--------------------------------------------------

To rewrite just some recent commits:

--------------------------------------------------
git filter-repo --invert-paths --path extraneous.txt --refs master~3..master
--------------------------------------------------

[[CALLBACKS]]
CALLBACKS
---------

For flexibility, filter-repo allows you to specify functions on the
command line to further filter all changes.  Please note that there
are some API compatibility caveats associated with these callbacks
that you should be aware of before using them; see the "API BACKWARD
COMPATIBILITY CAVEAT" comment near the top of git-filter-repo source
code.

All callback functions are of the same general format.  For a command line
argument like

--------------------------------------------------
--foo-callback 'BODY'
--------------------------------------------------

the following code will be compiled and called:

--------------------------------------------------
def foo_callback(foo):
  BODY
--------------------------------------------------

Thus, you just need to make sure your _BODY_ modifies and returns
_foo_ appropriately.  One important thing to note for all callbacks is
that filter-repo uses bytestrings (see
https://docs.python.org/3/library/stdtypes.html#bytes) everywhere
instead of strings.

There are four callbacks that allow you to operate directly on raw
objects that contain data that's easy to write in
linkgit:fast-import[1] format:

--------------------------------------------------
--blob-callback
--commit-callback
--tag-callback
--reset-callback
--------------------------------------------------

We'll come back to these later because it is often the case that the
other callbacks are more convenient.  The other callbacks operate on a
small piece of the raw objects or operate on pieces across multiple
types of raw object (e.g. author names and committer names and tagger
names across commits and tags, or refnames across commits, tags, and
resets, or messages across commits and tags).  The convenience
callbacks are:

--------------------------------------------------
--filename-callback
--message-callback
--name-callback
--email-callback
--refname-callback
--------------------------------------------------

in each you are expected to simply return a new value based on the one
passed in.  For example,

--------------------------------------------------
git-filter-repo --name-callback 'return name.replace(b"Wiliam", b"William")'
--------------------------------------------------

would result in the following function being called:

--------------------------------------------------
def name_callback(name):
  return name.replace(b"Wiliam", b"William")
--------------------------------------------------

The email callback is quite similar:

--------------------------------------------------
git-filter-repo --email-callback 'return email.replace(b".cm", b".com")'
--------------------------------------------------

The refname callback is also similar, but note that the refname passed in
and returned are expected to be fully qualified (e.g. b"refs/heads/master"
instead of just b"master" and b"refs/tags/v1.0.7" instead of b"1.0.7"):

--------------------------------------------------
git-filter-repo --refname-callback '
  # Change e.g. refs/heads/master to refs/heads/prefix-master
  rdir,rpath = os.path.split(refname)
  return rdir + b"/prefix-" + rpath'
--------------------------------------------------

The message callback is quite similar to the previous three callbacks,
though it operates on a bytestring that is likely more than one line:

--------------------------------------------------
git-filter-repo --message-callback '
  if b"Signed-off-by:" not in message:
    message += b"\nSigned-off-by: Me My <self@and.eye>"
  return re.sub(b"[Ee]-?[Mm][Aa][Ii][Ll]", b"email", message)'
--------------------------------------------------

The filename callback is slightly more interesting.  Returning None means
the file should be removed from all commits, returning the filename
unmodified marks the file to be kept, and returning a different name means
the file should be renamed.  An example:

--------------------------------------------------
git-filter-repo --filename-callback '
  if b"/src/" in filename:
    # Remove all files with a directory named "src" in their path
    # (except when "src" appears at the toplevel).
    return None
  elif filename.startswith(b"tools/"):
    # Rename tools/ -> scripts/misc/
    return b"scripts/misc/" + filename[6:]
  else:
    # Keep the filename and do not rename it
    return filename
  '
--------------------------------------------------

In contrast, the blob, reset, tag, and commit callbacks are not
expected to return a value, but are instead expected to modify the
object passed in.  Major fields for these objects are (subject to API
backward compatibility caveats mentioned previously):

  * Blob: `original_id` (original hash) and `data`
  * Reset: `ref` (name of reference) and `from_ref` (hash or integer mark)
  * Tag: `ref`, `from_ref`, `original_id`, `tagger_name`, `tagger_email`,
         `tagger_date`, `message`
  * Commit: `branch`, `original_id`, `author_name`, `author_email`,
            `author_date`, `committer_name`, `committer_email`,
            `committer_date `, `message`, `file_changes` (list of
            FileChange objects, each containing a `type`, `filename`,
            `mode`, and `blob_id`), `parents` (list of hashes or integer
            marks)

An example of each:

--------------------------------------------------
git filter-repo --blob-callback '
  if len(blob.data) > 25:
    # Mark this blob for removal from all commits
    blob.skip()
  else:
    blob.data = blob.data.sub(b"Hello", b"Goodbye")
  '
--------------------------------------------------

--------------------------------------------------
git filter-repo --reset-callback 'reset.ref = reset.ref.replace(b"master", b"dev")'
--------------------------------------------------

--------------------------------------------------
git filter-repo --tag-callback '
  if tag.tagger_name == b"Jim Williams":
    # Omit this tag
    tag.skip()
  else:
    tag.message = tag.message + b"\n\nTag of %s by %s on %s" % (tag.ref, tag.tagger_email, tag.tagger_date)'
--------------------------------------------------

--------------------------------------------------
git filter-repo --commit-callback '
  # Remove executable files with three 6s in their name (including
  # from leading directories).
  # Also, undo deletion of sources/foo/bar.txt (change types are
  # either b"D" (deletion) or b"M" (add or modify); renames are
  # handled by deleting the old file and adding a new one)
  commit.file_changes = [
         change for change in commit.file_changes
         if not (change.mode == b"100755" and
                 change.filename.count(b"6") == 3) and
            not (change.type == b"D" and
                 change.filename == b"sources/foo/bar.txt")]
  # Mark all .sh files as executable; modes in git are always one of
  # 100644 (normal file), 100755 (executable), 120000 (symlink), or
  # 160000 (submodule)
  for change in commit.file_changes:
    if change.filename.endswith(b".sh"):
      change.mode = b"100755"
  '
--------------------------------------------------

[[INTERNALS]]
INTERNALS
---------

You probably don't need to read this section unless you are just very
curious or you are trying to do a very complex history rewrite.

How filter-repo works
~~~~~~~~~~~~~~~~~~~~~

Roughly, filter-repo works by running

--------------------------------------------------
git fast-export <options> | filter | git fast-import <options>
--------------------------------------------------

where filter-repo not only launches the whole pipeline but also serves as
the _filter_ in the middle.  However, filter-repo does a few additional
things on top in order to make it into a well-rounded filtering tool.  A
sequence that more accurately reflects what filter-repo runs is:

  1. Verify we're in a fresh clone
  2. `git fetch -u . refs/remotes/origin/*:refs/heads/*`
  3. `git remote rm origin`
  4. `git fast-export --show-original-ids --reference-excluded-parents --fake-missing-tagger --signed-tags=strip --tag-of-filtered-object=rewrite --use-done-feature --no-data --reencode=yes --mark-tags --all | filter | git fast-import --force --quiet`
  5. `git update-ref --no-deref --stdin`, fed with a list of refs to nuke, and a list of replace refs to delete, create, or update.
  6. `git reset --hard`
  7. `git reflog expire --expire=now --all`
  8. `git gc --prune=now`

Some notes or exceptions on each of the above:

  1. If we're not in a fresh clone, users will not be able to recover if
     they used the wrong command or ran in the wrong repo.  (Though
     `--force` overrides this check, and it's also off if you've already
     ran filter-repo once in this repo.)
  2. Technically, we actually use a `git update-ref` command fed with a lot
     of input due to the fact that users can use `--force` when local
     branches might not match remote branches.  But this fetch command
     catches the intent rather succinctly.
  3. We don't want users accidentally pushing back to the original repo, as
     discussed in <<DISCUSSION>>.  It also reminds users that since history
     has been rewritten, this repo is no longer compatible with the
     original.  Finally, another minor benefit is this allows users to push
     with the `--mirror` option to their new home without accidentally
     sending remote tracking branches.
  4. Some of these flags are always used but others are actually
     conditional.  For example, filter-repo's `--replace-text` and
     `--blob-callback` options need to work on blobs so `--no-data` cannot
     be passed to fast-export.  But when we don't need to work on blobs,
     passing `--no-data` speeds things up.  Also, other flags may change
     the structure of the pipeline as well (e.g. `--dry-run` and `--debug`)
  5. We use this step to write replace refs for accessing the newly written
     commit hashes using their previous names.  Also, if refs were renamed
     by various steps, we need to delete the old refnames in order to avoid
     mixing old and new history.
  6. Users also have old versions of files in their working tree and index;
     we want those cleaned up to match the rewritten history as well.  Note
     that this step is skipped in bare repos.
  7. Reflogs will hold on to old history, so we need to expire them.
  8. We need to gc to avoid mixing new and old history.  Also, it shrinks
     the repository for users, so they don't have to do extra work.  (Odds
     are that they've only rewritten trees and commits and maybe a few
     blobs, so `--aggressive` isn't needed and would be too slow.)

Information about these steps is printed out when `--debug` is passed
to filter-repo.  When doing a `--partial` history rewrite, steps 2, 3,
7, and 8 are unconditionally skipped, step 5 is skipped if
`--replace-refs` is `update-no-add`, and just the nuke-unused-refs
portion of step 5 is skipped if `--replace-refs` is something else.

Limitations
~~~~~~~~~~~

Inherited limitations
^^^^^^^^^^^^^^^^^^^^^

Since git filter-repo calls fast-export and fast-import to do a lot of the
heavy lifting, it inherits limitations from those systems:

  * extended commit headers, if any, are stripped
  * commits get rewritten meaning they will have new hashes; therefore,
    signatures on commits and tags cannot continue to work and instead are
    just removed (thus signed tags become annotated tags)
  * tags of commits are supported.  Prior to git-2.24.0, tags of blobs and
    tags of tags are not supported (fast-export would die on such tags).
    tags of trees are not supported in any git version (since fast-export
    ignores tags of trees with a warning and fast-import provides no way to
    import them).
  * annotated and signed tags outside of the refs/tags/ namespace are not
    supported (their location will be mangled in weird ways)
  * fast-import will die on various forms of invalid input, such as a
    timezone with more than four digits
  * fast-export cannot reencode commit messages into UTF-8 if the commit
    message is not valid in its specified encoding (in such cases, it'll
    leave the commit message and the encoding header alone).
  * commits without an author will be given one matching the committer
  * tags without a tagger will be given a fake tagger
  * references that include commit cycles in their history (which can be
    created with linkgit:git-replace[1]) will not be flagged to the user as
    an error but will be silently deleted by fast-export as though the
    branch or tag contained no interesting files

There are also some limitations due to the design of these systems:

  * Trying to insert additional files into the stream can be tricky; since
    fast-export only lists file changes in a merge relative to its first
    parent, if you insert additional files into a commit that is in the
    second (or third or fourth) parent history of a merge, then you also
    need to add it to the merge manually.  (Similarly, if you change which
    parent is the first parent in a merge commit, you need to manually
    update the list of file changes to be relative to the new first
    parent.)

  * fast-export and fast-import work with exact file contents, not patches.
    (e.g. "Whatever the current contents of this file, update them to now
    have these contents") Because of this, removing the changes made in a
    single commit or inserting additional changes to a file in some commit
    and expecting them to propagate forward is not something that can be
    done with these tools.  Use linkgit:git-rebase[1] for that.

Intrinsic limitations
^^^^^^^^^^^^^^^^^^^^^

Some types of filtering have limitations that would affect any tool
attempting to perform them; the most any tool can do is attempt to notify
the user when it detects an issue:

  * When rewriting commit hashes in commit messages, there are a variety
    of cases when the hash will not be updated (whenever this happens, a
    note is written to `.git/filter-repo/suboptimal-issues`):
    * if a commit hash does not correspond to a commit in the old repo
    * if a commit hash corresponds to a commit that gets pruned
    * if an abbreviated hash is not unique

  * Pruning of empty commits can cause a merge commit to lose an entire
    ancestry line and become a non-merge.  If the merge commit had no
    changes then it can be pruned too, but if it still has changes it needs
    to be kept.  This might cause minor confusion since the commit will
    likely have a commit message that makes it sound like a merge commit
    even though it's not.  (Whenever a merge commit becomes a non-merge
    commit, a note is written to `.git/filter-repo/suboptimal-issues`)

Issues specific to filter-repo
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  * Multiple repositories in the wild have been observed which use a bogus
    timezone (`+051800`); google will find you some reports.  The intended
    timezone wasn't clear or wasn't always the same.  Replace with a
    different bogus timezone that fast-import will accept (`+0261`).

  * `--path-rename` can result in pathname collisions; to avoid excessive
    memory requirements of tracking which files are in all commits or
    looking up what files exist with either every commit or every usage of
    --path-rename, we just tell the user that they might clobber other
    changes if they aren't careful.  We can check if the clobbering comes
    from another --path-rename without much overhead.  (Perhaps in the
    future it's worth adding a slow mode to --path-rename that will do the
    more exhaustive checks?)

  * There is no mechanism for directly controlling which flags are passed
    to fast-export (or fast-import); only pre-defined flags can be turned
    on or off as a side-effect of other options.  Direct control would make
    little sense because some options like `--full-tree` would require
    additional code in filter-repo (to parse new directives), and others
    such as `-M` or `-C` would break assumptions used in other places of
    filter-repo.

  * Partial-repo filtering, while supported, runs counter to filter-repo's
    "avoid mixing old and new history" design.  This support has required
    improvements to core git as well (e.g. it depends upon the
    `--reference-excluded-parents` option to fast-export that was added
    specifically for this usage within filter-repo).  The `--partial` and
    `--refs` options will continue to be supported since there are people
    with usecases for them; however, I am concerned that this inconsistency
    about mixing old and new history seems likely to lead to user mistakes.
    For now, I just hope that long explanations of caveats in the
    documentation of these options suffice to curtail any such problems.

Comments on reversibility
^^^^^^^^^^^^^^^^^^^^^^^^^

Some people are interested in reversibility of of a rewrite; e.g. rewrite
history, possibly add some commits, then unrewrite and get the original
history back plus a few new "unrewritten" commits.  Obviously this is
impossible if your rewrite involves throwing away information
(e.g. filtering out files or replacing several different strings with
`***REMOVED***`), but may be possible with some rewrites.  filter-repo is
likely to be a poor fit for this type of workflow for a few reasons:

  * most of the limitations inherited from fast-export and fast-import
    are of a type that cause reversibility issues
  * grafts and replace refs, if present, are used in the rewrite and made
    permanent
  * rewriting of commit hashes will probably be reversible, but it is
    possible for rewritten abbreviated hashes to not be unique even if the
    original abbreviated hashes were.
  * filter-repo defaults to several forms of unreversible rewriting that
    you may need to turn off (e.g. the last two bullet points above or
    reencoding commit messages into UTF-8); it's possible that additional
    forms of unreversible rewrites will be added in the future.
  * I assume that people use filter-repo for one-shot conversions, not
    ongoing data transfers.  I explicitly reserve the right to change any
    API in filter-repo based on this presumption (and a comment to this
    effect is found in multiple places in the code and examples).  You
    have been warned.

SEE ALSO
--------
linkgit:git-rebase[1], linkgit:git-filter-branch[1]

GIT
---
Part of the linkgit:git[1] suite