git-filter-branch.sh - jrn/git - Git at Google

 #!/bin/sh
 #
 # Rewrite revision history
 # Copyright (c) Petr Baudis, 2006
 # Minimal changes to "port" it to core-git (c) Johannes Schindelin, 2007
 #
 # Lets you rewrite GIT revision history by creating a new branch from
 # your current branch by 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 takes the new branch name as a mandatory argument and
 # the filters as optional arguments. If you specify no filters, the
 # commits will be recommitted without any changes, which would normally
 # have no effect and result with the new branch pointing to the same
 # branch as your current branch. (Nevertheless, this may be useful in
 # the future for compensating for some Git bugs or such, therefore
 # such a usage is permitted.)
 #
 # WARNING! The rewritten history will have different ids 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. Please do
 # not use this command if you do not know the full implications, and
 # avoid using it anyway - do not do what a simple single commit on top
 # of the current version would fix.
 #
 # Always verify that the rewritten version is correct before disposing
 # the original branch.
 #
 # Note that since this operation is extensively I/O expensive, it might
 # be a good idea to do it off-disk, e.g. on tmpfs. Reportedly the speedup
 # is very noticeable.
 #
 # OPTIONS
 # -------
 # -d TEMPDIR:: The path to the temporary tree used for rewriting
 #	When applying a tree filter, the command needs to temporary
 #	checkout 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.
 #
 # Filters
 # ~~~~~~~
 # The filters are applied in the order as listed below. The COMMAND
 # argument is always evaluated in shell using the 'eval' command.
 # The $GIT_COMMIT environment variable is permanently set to contain
 # the id of the commit being rewritten. The author/committer environment
 # variables are set before the first filter is run.
 #
 # 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, fails otherwise; the 'map' function can return several
 # ids on separate lines if your commit filter emitted multiple commits
 # (see below).
 #
 # --env-filter COMMAND:: The filter for modifying environment
 #	This is the filter for modifying 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` for details). Do not forget to
 #	re-export the variables.
 #
 # --tree-filter COMMAND:: The filter for rewriting tree (and its contents)
 #	This is the filter for rewriting the tree and its contents.
 #	The COMMAND 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 - .gitignore files nor any other ignore rules
 #	HAVE NO EFFECT!).
 #
 # --index-filter COMMAND:: The filter for rewriting index
 #	This is the filter for rewriting the Git's directory index.
 #	It is similar to the tree filter but does not check out the
 #	tree, which makes it much faster. However, you must use the
 #	lowlevel Git index manipulation commands to do your work.
 #
 # --parent-filter COMMAND:: The filter for rewriting parents
 #	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
 #	format accepted by `git commit-tree`: empty for initial
 #	commit, "-p parent" for a normal commit and "-p parent1
 #	-p parent2 -p parent3 ..." for a merge commit.
 #
 # --msg-filter COMMAND:: The filter for rewriting commit message
 #	This is the filter for rewriting the commit messages.
 #	The COMMAND argument is evaluated in shell with the original
 #	commit message on standard input; its standard output is
 #	is used as the new commit message.
 #
 # --commit-filter COMMAND:: The filter for performing the commit
 #	If this filter is passed, it will be called instead of the
 #	`git commit-tree` command, with those arguments:
 #
 #		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, all of them will be used
 #	as parents instead of the original commit in further commits.
 #
 # --tag-name-filter COMMAND:: The filter for rewriting tag names.
 #	If this filter is 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.
 #
 #	Note that there is currently no support for proper rewriting of
 #	tag objects; in layman terms, if the tag has a message or signature
 #	attached, the rewritten tag won't have it. Sorry. (It is by
 #	definition impossible to preserve signatures at any rate, though.)
 #
 # --subdirectory-filter DIRECTORY:: Only regard the history, as seen by
 #	the given subdirectory. The result will contain that directory as
 #	its project root.
 #
 # EXAMPLE USAGE
 # -------------
 # Suppose you want to remove a file (containing confidential information
 # or copyright violation) from all commits:
 #
 #	git-filter-branch --tree-filter 'rm filename' newbranch
 #
 # A significantly faster version:
 #
 #	git-filter-branch --index-filter 'git update-index --remove filename' newbranch
 #
 # Now, you will get the rewritten history saved in the branch 'newbranch'
 # (your current branch is left untouched).
 #
 # To "etch-graft" a commit to the revision history (set a commit to be
 # the parent of the current initial commit and propagate that):
 #
 #	git-filter-branch --parent-filter sed\ 's/^$/-p graftcommitid/' newbranch
 #
 # (if the parent string is empty - therefore we are dealing with the
 # initial commit - add graftcommit as a parent). Note that this assumes
 # history with a single root (that is, no git-merge without common ancestors
 # happened). If this is not the case, use:
 #
 #	git-filter-branch --parent-filter 'cat; [ "$GIT_COMMIT" = "COMMIT" ] && echo "-p GRAFTCOMMIT"' newbranch
 #
 # To remove commits authored by "Darl McBribe" from the history:
 #
 #	git-filter-branch --commit-filter 'if [ "$GIT_AUTHOR_NAME" = "Darl McBribe" ]; then shift; while [ -n "$1" ]; do shift; echo "$1"; shift; done; else git commit-tree "$@"; fi' newbranch
 #
 # (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.
 #
 # 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 commits D,E,F,G,H, use:
 #
 #	git-filter-branch ... new-H C..H
 #
 # To rewrite commits E,F,G,H, use one of these:
 #
 #	git-filter-branch ... new-H C..H --not D
 #	git-filter-branch ... new-H 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' directorymoved

 # Testsuite: TODO

 set -e

 USAGE="git-filter-branch [-d TEMPDIR] [FILTERS] DESTBRANCH [REV-RANGE]"
 . git-sh-setup

 map()
 {
 	# if it was not rewritten, take the original
 	test -r "$workdir/../map/$1" || echo "$1"
 	cat "$workdir/../map/$1"
 }

 # When piped a commit, output a script to set the ident of either
 # "author" or "committer

 set_ident () {
 	lid="$(echo "$1" | tr "A-Z" "a-z")"
 	uid="$(echo "$1" | tr "a-z" "A-Z")"
 	pick_id_script='
 		/^'$lid' /{
 			s/'\''/'\''\\'\'\''/g
 			h
 			s/^'$lid' \([^<]*\) <[^>]*> .*$/\1/
 			s/'\''/'\''\'\'\''/g
 			s/.*/export GIT_'$uid'_NAME='\''&'\''/p

 			g
 			s/^'$lid' [^<]* <\([^>]*\)> .*$/\1/
 			s/'\''/'\''\'\'\''/g
 			s/.*/export GIT_'$uid'_EMAIL='\''&'\''/p

 			g
 			s/^'$lid' [^<]* <[^>]*> \(.*\)$/\1/
 			s/'\''/'\''\'\'\''/g
 			s/.*/export GIT_'$uid'_DATE='\''&'\''/p

 			q
 		}
 	'

 	LANG=C LC_ALL=C sed -ne "$pick_id_script"
 	# Ensure non-empty id name.
 	echo "[ -n \"\$GIT_${uid}_NAME\" ] || export GIT_${uid}_NAME=\"\${GIT_${uid}_EMAIL%%@*}\""
 }

 tempdir=.git-rewrite
 filter_env=
 filter_tree=
 filter_index=
 filter_parent=
 filter_msg=cat
 filter_commit='git commit-tree "$@"'
 filter_tag_name=
 filter_subdir=
 while case "$#" in 0) usage;; esac
 do
 	case "$1" in
 	--)
 		shift
 		break
 		;;
 	-*)
 		;;
 	*)
 		break;
 	esac

 	# all switches take one argument
 	ARG="$1"
 	case "$#" in 1) usage ;; esac
 	shift
 	OPTARG="$1"
 	shift

 	case "$ARG" in
 	-d)
 		tempdir="$OPTARG"
 		;;
 	--env-filter)
 		filter_env="$OPTARG"
 		;;
 	--tree-filter)
 		filter_tree="$OPTARG"
 		;;
 	--index-filter)
 		filter_index="$OPTARG"
 		;;
 	--parent-filter)
 		filter_parent="$OPTARG"
 		;;
 	--msg-filter)
 		filter_msg="$OPTARG"
 		;;
 	--commit-filter)
 		filter_commit="$OPTARG"
 		;;
 	--tag-name-filter)
 		filter_tag_name="$OPTARG"
 		;;
 	--subdirectory-filter)
 		filter_subdir="$OPTARG"
 		;;
 	*)
 		usage
 		;;
 	esac
 done

 dstbranch="$1"
 shift
 test -n "$dstbranch" || die "missing branch name"
 git show-ref "refs/heads/$dstbranch" 2> /dev/null &&
 	die "branch $dstbranch already exists"

 test ! -e "$tempdir" || die "$tempdir already exists, please remove it"
 mkdir -p "$tempdir/t"
 cd "$tempdir/t"
 workdir="$(pwd)"

 case "$GIT_DIR" in
 /*)
 	;;
 *)
 	GIT_DIR="$(pwd)/../../$GIT_DIR"
 	;;
 esac
 export GIT_DIR GIT_WORK_TREE=.

 export GIT_INDEX_FILE="$(pwd)/../index"
 git read-tree # seed the index file

 ret=0


 mkdir ../map # map old->new commit ids for rewriting parents

 case "$filter_subdir" in
 "")
 	git rev-list --reverse --topo-order --default HEAD \
 		--parents "$@"
 	;;
 *)
 	git rev-list --reverse --topo-order --default HEAD \
 		--parents --full-history "$@" -- "$filter_subdir"
 esac > ../revs
 commits=$(cat ../revs | wc -l | tr -d " ")

 test $commits -eq 0 && die "Found nothing to rewrite"

 i=0
 while read commit parents; do
 	i=$(($i+1))
 	printf "$commit ($i/$commits) "

 	case "$filter_subdir" in
 	"")
 		git read-tree -i -m $commit
 		;;
 	*)
 		git read-tree -i -m $commit:"$filter_subdir"
 	esac

 	export GIT_COMMIT=$commit
 	git cat-file commit "$commit" >../commit

 	eval "$(set_ident AUTHOR <../commit)"
 	eval "$(set_ident COMMITTER <../commit)"
 	eval "$filter_env" < /dev/null

 	if [ "$filter_tree" ]; then
 		git checkout-index -f -u -a
 		# files that $commit removed are now still in the working tree;
 		# remove them, else they would be added again
 		git ls-files -z --others | xargs -0 rm -f
 		eval "$filter_tree" < /dev/null
 		git diff-index -r $commit | cut -f 2- | tr '\n' '\0' | \
 			xargs -0 git update-index --add --replace --remove
 		git ls-files -z --others | \
 			xargs -0 git update-index --add --replace --remove
 	fi

 	eval "$filter_index" < /dev/null

 	parentstr=
 	for parent in $parents; do
 		for reparent in $(map "$parent"); do
 			parentstr="$parentstr -p $reparent"
 		done
 	done
 	if [ "$filter_parent" ]; then
 		parentstr="$(echo "$parentstr" | eval "$filter_parent")"
 	fi

 	sed -e '1,/^$/d' <../commit | \
 		eval "$filter_msg" | \
 		sh -c "$filter_commit" "git commit-tree" $(git write-tree) $parentstr | \
 		tee ../map/$commit
 done <../revs

 src_head=$(tail -n 1 ../revs | sed -e 's/ .*//')
 target_head=$(head -n 1 ../map/$src_head)
 case "$target_head" in
 '')
 	echo Nothing rewritten
 	;;
 *)
 	git update-ref refs/heads/"$dstbranch" $target_head
 	if [ $(cat ../map/$src_head | wc -l) -gt 1 ]; then
 		echo "WARNING: Your commit filter caused the head commit to expand to several rewritten commits. Only the first such commit was recorded as the current $dstbranch head but you will need to resolve the situation now (probably by manually merging the other commits). These are all the commits:" >&2
 		sed 's/^/	/' ../map/$src_head >&2
 		ret=1
 	fi
 	;;
 esac

 if [ "$filter_tag_name" ]; then
 	git for-each-ref --format='%(objectname) %(objecttype) %(refname)' refs/tags |
 	while read sha1 type ref; do
 		ref="${ref#refs/tags/}"
 		# XXX: Rewrite tagged trees as well?
 		if [ "$type" != "commit" -a "$type" != "tag" ]; then
 			continue;
 		fi

 		if [ "$type" = "tag" ]; then
 			# Dereference to a commit
 			sha1t="$sha1"
 			sha1="$(git rev-parse "$sha1"^{commit} 2>/dev/null)" || continue
 		fi

 		[ -f "../map/$sha1" ] || continue
 		new_sha1="$(cat "../map/$sha1")"
 		export GIT_COMMIT="$sha1"
 		new_ref="$(echo "$ref" | eval "$filter_tag_name")"

 		echo "$ref -> $new_ref ($sha1 -> $new_sha1)"

 		if [ "$type" = "tag" ]; then
 			# Warn that we are not rewriting the tag object itself.
 			warn "unreferencing tag object $sha1t"
 		fi

 		git update-ref "refs/tags/$new_ref" "$new_sha1"
 	done
 fi

 cd ../..
 rm -rf "$tempdir"
 echo "Rewritten history saved to the $dstbranch branch"

 exit $ret
	#!/bin/sh
	#
	# Rewrite revision history
	# Copyright (c) Petr Baudis, 2006
	# Minimal changes to "port" it to core-git (c) Johannes Schindelin, 2007
	#
	# Lets you rewrite GIT revision history by creating a new branch from
	# your current branch by 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 takes the new branch name as a mandatory argument and
	# the filters as optional arguments. If you specify no filters, the
	# commits will be recommitted without any changes, which would normally
	# have no effect and result with the new branch pointing to the same
	# branch as your current branch. (Nevertheless, this may be useful in
	# the future for compensating for some Git bugs or such, therefore
	# such a usage is permitted.)
	#
	# WARNING! The rewritten history will have different ids 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. Please do
	# not use this command if you do not know the full implications, and
	# avoid using it anyway - do not do what a simple single commit on top
	# of the current version would fix.
	#
	# Always verify that the rewritten version is correct before disposing
	# the original branch.
	#
	# Note that since this operation is extensively I/O expensive, it might
	# be a good idea to do it off-disk, e.g. on tmpfs. Reportedly the speedup
	# is very noticeable.
	#
	# OPTIONS
	# -------
	# -d TEMPDIR:: The path to the temporary tree used for rewriting
	# When applying a tree filter, the command needs to temporary
	# checkout 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.
	#
	# Filters
	# ~~~~~~~
	# The filters are applied in the order as listed below. The COMMAND
	# argument is always evaluated in shell using the 'eval' command.
	# The $GIT_COMMIT environment variable is permanently set to contain
	# the id of the commit being rewritten. The author/committer environment
	# variables are set before the first filter is run.
	#
	# 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, fails otherwise; the 'map' function can return several
	# ids on separate lines if your commit filter emitted multiple commits
	# (see below).
	#
	# --env-filter COMMAND:: The filter for modifying environment
	# This is the filter for modifying 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` for details). Do not forget to
	# re-export the variables.
	#
	# --tree-filter COMMAND:: The filter for rewriting tree (and its contents)
	# This is the filter for rewriting the tree and its contents.
	# The COMMAND 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 - .gitignore files nor any other ignore rules
	# HAVE NO EFFECT!).
	#
	# --index-filter COMMAND:: The filter for rewriting index
	# This is the filter for rewriting the Git's directory index.
	# It is similar to the tree filter but does not check out the
	# tree, which makes it much faster. However, you must use the
	# lowlevel Git index manipulation commands to do your work.
	#
	# --parent-filter COMMAND:: The filter for rewriting parents
	# 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
	# format accepted by `git commit-tree`: empty for initial
	# commit, "-p parent" for a normal commit and "-p parent1
	# -p parent2 -p parent3 ..." for a merge commit.
	#
	# --msg-filter COMMAND:: The filter for rewriting commit message
	# This is the filter for rewriting the commit messages.
	# The COMMAND argument is evaluated in shell with the original
	# commit message on standard input; its standard output is
	# is used as the new commit message.
	#
	# --commit-filter COMMAND:: The filter for performing the commit
	# If this filter is passed, it will be called instead of the
	# `git commit-tree` command, with those arguments:
	#
	# 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, all of them will be used
	# as parents instead of the original commit in further commits.
	#
	# --tag-name-filter COMMAND:: The filter for rewriting tag names.
	# If this filter is 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.
	#
	# Note that there is currently no support for proper rewriting of
	# tag objects; in layman terms, if the tag has a message or signature
	# attached, the rewritten tag won't have it. Sorry. (It is by
	# definition impossible to preserve signatures at any rate, though.)
	#
	# --subdirectory-filter DIRECTORY:: Only regard the history, as seen by
	# the given subdirectory. The result will contain that directory as
	# its project root.
	#
	# EXAMPLE USAGE
	# -------------
	# Suppose you want to remove a file (containing confidential information
	# or copyright violation) from all commits:
	#
	# git-filter-branch --tree-filter 'rm filename' newbranch
	#
	# A significantly faster version:
	#
	# git-filter-branch --index-filter 'git update-index --remove filename' newbranch
	#
	# Now, you will get the rewritten history saved in the branch 'newbranch'
	# (your current branch is left untouched).
	#
	# To "etch-graft" a commit to the revision history (set a commit to be
	# the parent of the current initial commit and propagate that):
	#
	# git-filter-branch --parent-filter sed\ 's/^$/-p graftcommitid/' newbranch
	#
	# (if the parent string is empty - therefore we are dealing with the
	# initial commit - add graftcommit as a parent). Note that this assumes
	# history with a single root (that is, no git-merge without common ancestors
	# happened). If this is not the case, use:
	#
	# git-filter-branch --parent-filter 'cat; [ "$GIT_COMMIT" = "COMMIT" ] && echo "-p GRAFTCOMMIT"' newbranch
	#
	# To remove commits authored by "Darl McBribe" from the history:
	#
	# git-filter-branch --commit-filter 'if [ "$GIT_AUTHOR_NAME" = "Darl McBribe" ]; then shift; while [ -n "$1" ]; do shift; echo "$1"; shift; done; else git commit-tree "$@"; fi' newbranch
	#
	# (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.
	#
	# 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 commits D,E,F,G,H, use:
	#
	# git-filter-branch ... new-H C..H
	#
	# To rewrite commits E,F,G,H, use one of these:
	#
	# git-filter-branch ... new-H C..H --not D
	# git-filter-branch ... new-H 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' directorymoved

	# Testsuite: TODO

	set -e

	USAGE="git-filter-branch [-d TEMPDIR] [FILTERS] DESTBRANCH [REV-RANGE]"
	. git-sh-setup

	map()
	{
	# if it was not rewritten, take the original
	test -r "$workdir/../map/$1" \|\| echo "$1"
	cat "$workdir/../map/$1"
	}

	# When piped a commit, output a script to set the ident of either
	# "author" or "committer

	set_ident () {
	lid="$(echo "$1" \| tr "A-Z" "a-z")"
	uid="$(echo "$1" \| tr "a-z" "A-Z")"
	pick_id_script='
	/^'$lid' /{
	s/'\''/'\''\\'\'\''/g
	h
	s/^'$lid' \([^<]\) <[^>]> .*$/\1/
	s/'\''/'\''\'\'\''/g
	s/.*/export GIT_'$uid'_NAME='\''&'\''/p

	g
	s/^'$lid' [^<]* <\([^>]\)> .$/\1/
	s/'\''/'\''\'\'\''/g
	s/.*/export GIT_'$uid'_EMAIL='\''&'\''/p

	g
	s/^'$lid' [^<]* <[^>]> \(.\)$/\1/
	s/'\''/'\''\'\'\''/g
	s/.*/export GIT_'$uid'_DATE='\''&'\''/p

	q
	}
	'

	LANG=C LC_ALL=C sed -ne "$pick_id_script"
	# Ensure non-empty id name.
	echo "[ -n \"\$GIT_${uid}_NAME\" ] \|\| export GIT_${uid}_NAME=\"\${GIT_${uid}_EMAIL%%@*}\""
	}

	tempdir=.git-rewrite
	filter_env=
	filter_tree=
	filter_index=
	filter_parent=
	filter_msg=cat
	filter_commit='git commit-tree "$@"'
	filter_tag_name=
	filter_subdir=
	while case "$#" in 0) usage;; esac
	do
	case "$1" in
	--)
	shift
	break
	;;
	-*)
	;;
	*)
	break;
	esac

	# all switches take one argument
	ARG="$1"
	case "$#" in 1) usage ;; esac
	shift
	OPTARG="$1"
	shift

	case "$ARG" in
	-d)
	tempdir="$OPTARG"
	;;
	--env-filter)
	filter_env="$OPTARG"
	;;
	--tree-filter)
	filter_tree="$OPTARG"
	;;
	--index-filter)
	filter_index="$OPTARG"
	;;
	--parent-filter)
	filter_parent="$OPTARG"
	;;
	--msg-filter)
	filter_msg="$OPTARG"
	;;
	--commit-filter)
	filter_commit="$OPTARG"
	;;
	--tag-name-filter)
	filter_tag_name="$OPTARG"
	;;
	--subdirectory-filter)
	filter_subdir="$OPTARG"
	;;
	*)
	usage
	;;
	esac
	done

	dstbranch="$1"
	shift
	test -n "$dstbranch" \|\| die "missing branch name"
	git show-ref "refs/heads/$dstbranch" 2> /dev/null &&
	die "branch $dstbranch already exists"

	test ! -e "$tempdir" \|\| die "$tempdir already exists, please remove it"
	mkdir -p "$tempdir/t"
	cd "$tempdir/t"
	workdir="$(pwd)"

	case "$GIT_DIR" in
	/*)
	;;
	*)
	GIT_DIR="$(pwd)/../../$GIT_DIR"
	;;
	esac
	export GIT_DIR GIT_WORK_TREE=.

	export GIT_INDEX_FILE="$(pwd)/../index"
	git read-tree # seed the index file

	ret=0


	mkdir ../map # map old->new commit ids for rewriting parents

	case "$filter_subdir" in
	"")
	git rev-list --reverse --topo-order --default HEAD \
	--parents "$@"
	;;
	*)
	git rev-list --reverse --topo-order --default HEAD \
	--parents --full-history "$@" -- "$filter_subdir"
	esac > ../revs
	commits=$(cat ../revs \| wc -l \| tr -d " ")

	test $commits -eq 0 && die "Found nothing to rewrite"

	i=0
	while read commit parents; do
	i=$(($i+1))
	printf "$commit ($i/$commits) "

	case "$filter_subdir" in
	"")
	git read-tree -i -m $commit
	;;
	*)
	git read-tree -i -m $commit:"$filter_subdir"
	esac

	export GIT_COMMIT=$commit
	git cat-file commit "$commit" >../commit

	eval "$(set_ident AUTHOR <../commit)"
	eval "$(set_ident COMMITTER <../commit)"
	eval "$filter_env" < /dev/null

	if [ "$filter_tree" ]; then
	git checkout-index -f -u -a
	# files that $commit removed are now still in the working tree;
	# remove them, else they would be added again
	git ls-files -z --others \| xargs -0 rm -f
	eval "$filter_tree" < /dev/null
	git diff-index -r $commit \| cut -f 2- \| tr '\n' '\0' \| \
	xargs -0 git update-index --add --replace --remove
	git ls-files -z --others \| \
	xargs -0 git update-index --add --replace --remove
	fi

	eval "$filter_index" < /dev/null

	parentstr=
	for parent in $parents; do
	for reparent in $(map "$parent"); do
	parentstr="$parentstr -p $reparent"
	done
	done
	if [ "$filter_parent" ]; then
	parentstr="$(echo "$parentstr" \| eval "$filter_parent")"
	fi

	sed -e '1,/^$/d' <../commit \| \
	eval "$filter_msg" \| \
	sh -c "$filter_commit" "git commit-tree" $(git write-tree) $parentstr \| \
	tee ../map/$commit
	done <../revs

	src_head=$(tail -n 1 ../revs \| sed -e 's/ .*//')
	target_head=$(head -n 1 ../map/$src_head)
	case "$target_head" in
	'')
	echo Nothing rewritten
	;;
	*)
	git update-ref refs/heads/"$dstbranch" $target_head
	if [ $(cat ../map/$src_head \| wc -l) -gt 1 ]; then
	echo "WARNING: Your commit filter caused the head commit to expand to several rewritten commits. Only the first such commit was recorded as the current $dstbranch head but you will need to resolve the situation now (probably by manually merging the other commits). These are all the commits:" >&2
	sed 's/^/ /' ../map/$src_head >&2
	ret=1
	fi
	;;
	esac

	if [ "$filter_tag_name" ]; then
	git for-each-ref --format='%(objectname) %(objecttype) %(refname)' refs/tags \|
	while read sha1 type ref; do
	ref="${ref#refs/tags/}"
	# XXX: Rewrite tagged trees as well?
	if [ "$type" != "commit" -a "$type" != "tag" ]; then
	continue;
	fi

	if [ "$type" = "tag" ]; then
	# Dereference to a commit
	sha1t="$sha1"
	sha1="$(git rev-parse "$sha1"^{commit} 2>/dev/null)" \|\| continue
	fi

	[ -f "../map/$sha1" ] \|\| continue
	new_sha1="$(cat "../map/$sha1")"
	export GIT_COMMIT="$sha1"
	new_ref="$(echo "$ref" \| eval "$filter_tag_name")"

	echo "$ref -> $new_ref ($sha1 -> $new_sha1)"

	if [ "$type" = "tag" ]; then
	# Warn that we are not rewriting the tag object itself.
	warn "unreferencing tag object $sha1t"
	fi

	git update-ref "refs/tags/$new_ref" "$new_sha1"
	done
	fi

	cd ../..
	rm -rf "$tempdir"
	echo "Rewritten history saved to the $dstbranch branch"

	exit $ret