GIT-FILTER-BRANCH(1)                                      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. If you have any grafts
       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 set according to the
       current commit. The values of these variables after the filters have
       run, are used for the new commit. 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&#8217;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&#8217;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 [xref to refsect2].


       --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 [xref to refsect2].


   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&#8217;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.


       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"





       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.


       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>"





       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.


       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:


       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&#8217;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).

GIT
       Part of the git(1) suite




                                                          GIT-FILTER-BRANCH(1)
