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

NAME
       git-filter-branch - Rewrite branches

SYNOPSIS
       git filter-branch [--env-filter ] [--tree-filter ]
               [--index-filter ] [--parent-filter ]
               [--msg-filter ] [--commit-filter ]
               [--tag-name-filter ] [--subdirectory-filter ]
               [--prune-empty]
               [--original ] [-d ] [-f | --force]
               [--] [...]

DESCRIPTION
       Lets you rewrite Git revision history by rewriting the branches mentioned in the , 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  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  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 
           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 
           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 
           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 
           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 
           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 
           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 "
           [(-p )...]" 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 
           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 
           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 
           Use this option to set the namespace where the original commits will be stored. The
           default value is refs/original.

       -d 
           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.

       ...
           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 /"' 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 =  && echo "-p " || 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 "
           ' 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

Git 2.7.4                                   03/23/2016                       GIT-FILTER-BRANCH(1)

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