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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 <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 <bunny@bugzilla.org>"
           ' HEAD~10..HEAD


       The --env-filter option can be used to modify committer and/or author identity. For example, if you
       found out that your commits have the wrong identity due to a misconfigured user.email, you can make a
       correction, before publishing the project, like this:

           git filter-branch --env-filter '
                   if test "$GIT_AUTHOR_EMAIL" = "root@localhost"
                   then
                           GIT_AUTHOR_EMAIL=john@example.com
                           export GIT_AUTHOR_EMAIL
                   fi
                   if test "$GIT_COMMITTER_EMAIL" = "root@localhost"
                   then
                           GIT_COMMITTER_EMAIL=john@example.com
                           export GIT_COMMITTER_EMAIL
                   fi
           ' -- --all


       To restrict rewriting to only part of the history, specify a revision range in addition to the new
       branch name. The new branch name will point to the top-most revision that a git rev-list of this
       range will print.

       Consider this history:

                D--E--F--G--H
               /     /
           A--B-----C


       To rewrite only commits D,E,F,G,H, but leave A, B and C alone, use:

           git filter-branch ... C..H


       To rewrite commits E,F,G,H, use one of these:

           git filter-branch ... C..H --not D
           git filter-branch ... D..H --not C


       To move the whole tree into a subdirectory, or remove it from there:

           git filter-branch --index-filter \
                   'git ls-files -s | sed "s-\t\"*-&newsubdir/-" |
                           GIT_INDEX_FILE=$GIT_INDEX_FILE.new \
                                   git update-index --index-info &&
                    mv "$GIT_INDEX_FILE.new" "$GIT_INDEX_FILE"' HEAD


CHECKLIST FOR SHRINKING A REPOSITORY
       git-filter-branch is often 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).

GIT
       Part of the git(1) suite



Git 1.8.3                                        05/24/2013                             GIT-FILTER-BRANCH(1)

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