git-transplant.sh

#!/bin/sh

USAGE='[-b <branch>] [--interactive | -i] [-v] [--quiet | -q] <base> [<target>]'
SUBDIRECTORY_OK=Yes
. git-sh-setup

rebase_options=

set -e

while test $# != 0
do
  case "$1" in
  -b)
    test 2 -le "$#" || usage
    branch="$2"
    shift
    ;;
  -i|--interactive|-v|-q|--quiet)
    rebase_options="$rebase_options $1"
    ;;
  -*)
    usage
    ;;
  *)
    break
    ;;
  esac
  shift
done

test $# -lt 1 && usage
test $# -gt 2 && usage

base=$1
target=$2

if test -z "$target"
then
  target="$base"
fi

head=$(git symbolic-ref HEAD) || die "Must be on a branch."

# Save $target in case we change it below
old_target=$(git rev-parse "$target")

if test -n "$branch"
then
  git checkout -q -b "$branch"
else
  git checkout -q -B "$target"
fi
git update-ref -m "Transplanting '$head'" "$head" "$base"

if test "$target" != "$base"
then
  git rebase $rebase_options --onto "$old_target" "$base"
fi