Merge two git repositories--move one into another--while retaining history of both

git-mv-remember.sh

#!/bin/bash

# License: http://www.apache.org/licenses/LICENSE-2.0
# Description: Merge two git repositories--move one into another--while retaining history of both
# WARNING: Before using, backup both repositories.
# Usage: ./git-mv-remember.sh repo_a repo_b relative/path/to/move/a/to/inside/of/b
# Example:
#	Repo A:
# 		A/.git
# 		A/foo1.txt
#		A/foo2.txt
#	Repo B:
#		B/.git
#		B/bar1.txt
#		B/bar2.txt
#	./git-mv-remember.sh A B lib/A
#		B/.git
#		B/bar1.txt
#		B/bar2.txt
#		B/lib/A/foo1.txt
# 		B/lib/A/foo2.txt

if [ ! $# == 3 ]; then
    echo "Usage: $0 repo_a repo_b relative/path/to/move/a/to/in/b"
    exit
fi

# Get absolute paths
FROM=`cd "$1"; pwd`
TO=`cd "$2"; pwd`

# Remove trailing slash
PREFIX=${3%/}

# Get a proper tab for mac's sed
TAB=`echo -e "\t"`

cd $FROM
git filter-branch --index-filter "git ls-files -s | sed \"s,\(.*\)$TAB\(.*\),\1$TAB$PREFIX/\2,\" | GIT_INDEX_FILE=\$GIT_INDEX_FILE.new git update-index --index-info && mv \$GIT_INDEX_FILE.new \$GIT_INDEX_FILE" HEAD
cd $TO
git pull $FROM