git-filter-branch(1)



GIT-FILTER-BRANCH(1)              Git Manual              GIT-FILTER-BRANCH(1)

NAME
       git-filter-branch - Rewrite branches

SYNOPSIS
       git filter-branch [--setup <command>] [--subdirectory-filter <directory>]
               [--env-filter <command>] [--tree-filter <command>]
               [--index-filter <command>] [--parent-filter <command>]
               [--msg-filter <command>] [--commit-filter <command>]
               [--tag-name-filter <command>] [--prune-empty]
               [--original <namespace>] [-d <directory>] [-f | --force]
               [--state-branch <branch>] [--] [<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
       --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.

       --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".

       --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.

       --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.

       --state-branch <branch>
           This option will cause the mapping from old to new objects to be
           loaded from named branch upon startup and saved as a new commit to
           that branch upon exit, enabling incremental of large trees. If
           <branch> does not exist it will be created.

       <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 "$GIT_AUTHOR_EMAIL" = "root@localhost"
                   then
                           GIT_AUTHOR_EMAIL=john@example.com
                   fi
                   if test "$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

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:

       o   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.

       o   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.

       o   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.

       o   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.

       o   Expire all reflogs with git reflog expire --expire=now --all.

       o   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:

       o   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.

       o   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.

       o   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

Git 2.15.0                        10/30/2017              GIT-FILTER-BRANCH(1)

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