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+git-filter-branch(1)
+====================
+
+NAME
+----
+git-filter-branch - Rewrite branches
+
+SYNOPSIS
+--------
+[verse]
+'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 linkgit: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 linkgit: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 linkgit: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 linkgit: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 linkgit: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 <<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 <<Remap_to_ancestor>>.
+
+
+[[Remap_to_ancestor]]
+Remap to ancestor
+~~~~~~~~~~~~~~~~~
+
+By using linkgit: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
+ 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 linkgit: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
+http://rtyley.github.io/bfg-repo-cleaner/[The BFG Repo-Cleaner],
+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 http://rtyley.github.io/bfg-repo-cleaner/#examples[command options]
+ 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 linkgit:git[1] suite