merge_git_repos.sh

#!/bin/bash

SOURCE_REPO="/local/path/to/source/repo"
REMOTE_NAME="github"
REMOTE_PATH="https://github.com/username/repo.git"
REMOTE_BRANCH="master"

# Prepare source repo.
cd ${SOURCE_REPO}
find . -not \( -name .git -prune \) -exec git rm -r {} \;
git commit -m "Remove source files"

# Merge remote repo files and history into source repo.
git remote add -f ${REMOTE_NAME} ${REMOTE_PATH}
git merge --no-edit ${REMOTE_NAME}/${REMOTE_BRANCH}

# Clean up
git remote remove ${REMOTE_NAME}