Script for moving branches from one git-svn mirror to a new one

portbranch.sh

#!/bin/bash
# Call like ./portbranch official-upstream/3.0 my-3.0-fixes

# Original Author:
# 2012 Ryan Pavlik <rpavlik@iastate.edu> <abiryan@ryand.net>
# http://academic.cleardefinition.com
# Iowa State University HCI Graduate Program/VRAC
#
# Copyright Iowa State University 2012.
# Distributed under the Boost Software License, Version 1.0.
# (See accompanying file LICENSE_1_0.txt or copy at
# http://www.boost.org/LICENSE_1_0.txt)

USAGE="<newupstreambranch> [<yourbranch>]"
LONG_USAGE=$(cat <<EOS
Port a branch between two different git-svn imports of the same original
repository.

If a branch is not specified, the current branch is used.
EOS
)

# Setup git stuff
. "$(git --exec-path)/git-sh-setup"

if [ "$1" == "-h" ]; then
    usage
fi

require_work_tree
require_clean_work_tree portbranch "Please commit them - stashes would be left behind."

YOUR_REMOTE=origin

function verifyLocalBranch() {
    branchname=$1
	git show-ref --verify --quiet "refs/heads/${branchname}" || git branch "${branchname}" "${YOUR_REMOTE}/${branchname}"
}

function getCommitSubject() {
	git log --pretty=format:'%s' -n 1 $1
}

upstream_branch=$1
your_branch=$2

# Simultaneously check for detached head and fill in your_branch if you only
# passed one argument
if current_branch=$(git symbolic-ref -q HEAD); then
	case "$#" in
	1)
		your_branch="${current_branch}"
		;;
	esac
else
	die "You're currently on a detached head!"
fi

verifyLocalBranch "${your_branch}"

# Step 1: Find the latest commit on ${your_branch} that was from git-svn
if parenthash=$(git log --fixed-strings --grep="git-svn-id:" --pretty=format:"%H" -n 1 "${your_branch}"); then
    # The following grabs, from the commit message body's line that includes git-svn-id,
    # the last two fields (a sort of SVN URL and an apparent GUID), then strips off
    # everything up to and including the domain name to use as a unique ID for that commit.
    # The domain removal is so that anonymous vs. logged-in svn repos should hopefully be OK -
    # it's just a heuristic that works for Google Code.
	parentsvnid=$(git log ${parenthash} -n 1 --pretty=format:"%b" | grep "git-svn-id" | cut --delimiter=" " -f 2-3 | sed 's_[^/]*//[^/]*__')
else
	die "No commits in this branch have a git-svn-id listed in their commit messsage!"
fi

# Step 2: Find the matching commit

if ontohash=$(git log --fixed-strings --grep="${parentsvnid}" --pretty=format:"%H" "${upstream_branch}" -n 1); then
	# we got one, I think! Now just make sure there are no common ancestors...
	if git merge-base ${parenthash} ${ontohash} > /dev/null; then
		die "Apparent branch-point ${parenthash} and located matching commit ${ontohash} have a common ancestor!"
	fi
else
	die "Could not find a match for branch point commit ${parenthash}"
fi


#Step 3: Perform the rebase to transplant ${your_branch}

say "Old parent commit:"
GIT_PAGER=cat git log -n 1 -s ${parenthash}

say
say "New parent commit:"
GIT_PAGER=cat git log -n 1 -s ${ontohash}

say
say "The command we are about to run is:"
say "	git rebase --onto=${ontohash} ${parenthash} ${your_branch}"
say "From here on out, it's up to git rebase - this script is done."
say "Continue? [yn]"

read CONFIRM
if [ "${CONFIRM}" == "y" ]; then
	exec git rebase --onto=${ontohash} ${parenthash} ${your_branch}
else
	say "Didn't get 'y', exiting without rebasing."
fi