This script splits a subfolder of an existing git repo into its own separate repo. It will preserve all tags by default, and any branches specified with '-b'. Usage example: ./git-split-subfolder.sh -p git://repo.com/foo -services -s mysubfolder -b "branch1 branch2 branch3" The new repo 'mysubfolder' will be in the $CWD.

git-split-subfolder.sh

#!/bin/bash
set -e

usage() {
cat << EOF
usage: $0 [options]

This script splits an existing folder inside of a git repo into its own
separate git repo, optionally preserving all existing tags and branches from the
parent repo.

OPTIONS:
   -h      Show this message
   -p      URI / Path to parent repo
   -s      Subfolder name
   -b      List of any branches to preserve i.e '-b "branch1 branch2 branch3"'
   -c      Don't run any pruning or gc on the new repo
   -t      Don't bring over existing branches and tags
EOF
}

PARENT_REPO_URI=
SUBFOLDER_NAME=
PRESERVE_BRANCHES=
NO_CLEANUP=
TAGS_AND_BRANCHES="-- --all"
while getopts “hs:p:b:c:t:” OPTION
do
    case $OPTION in
        h)
            usage
            exit 1
            ;;
        p)
            PARENT_REPO_URI=$OPTARG
            ;;
        s)
            SUBFOLDER_NAME=$OPTARG
            ;;
        b)
            PRESERVE_BRANCHES=$OPTARG
            ;;
        c)
            NO_CLEANUP=true
            ;;
        t)
            TAGS_AND_BRANCHES=""
            ;;
        ?)
            usage
            exit
            ;;
    esac
done

if [ -z "${PARENT_REPO_URI}" ] || [ -z "${SUBFOLDER_NAME}" ];
then
    usage
    exit 1
fi

function cleanup {
    header "Performing GC on the new repo"
    git reset --hard
    git for-each-ref --format="%(refname)" refs/original/ | xargs -n 1 git update-ref -d
    git reflog expire --expire=now --all
    git gc --aggressive --prune=now
}

function header {
    echo "---- $1 ----"
}

header "Cloning existing repo at ${PARENT_REPO_URI}"
git clone $PARENT_REPO_URI $SUBFOLDER_NAME
pushd $SUBFOLDER_NAME


if [[ "${PRESERVE_BRANCHES}" ]] && [[ "${TAGS_AND_BRANCHES}" ]]
then
    header "Setting up tracking for existing branches"
    pushd $SUBFOLDER_NAME
    for branch in $PRESERVE_BRANCHES
    do
        git branch -t $branch origin/$branch
    done
    popd
fi

header "Removing existing remote origin"
git remote remove origin

header "Filtering the branch"
git filter-branch --tag-name-filter cat --prune-empty --subdirectory-filter $SUBFOLDER_NAME $TAGS_AND_BRANCHES

if [ -z "$NO_CLEANUP" ]
then
    cleanup
fi

header "Done!"