A shell script to merge one git repository into another, including all branches and tags

repo-merge.sh

#!/bin/bash
set -e

# Merge this repo
SRCREPO=$1; shift
# into this one
DSTREPO=$1; shift
# at this path
BASENAME=$1; shift
# and apply this patch when done
PATCHFILE=""
if [[ $1 != "" ]]; then
    PATCHFILE=$1; shift
fi

SRCNAME=$(basename ${SRCREPO} | sed -e 's/\(.*\)\..*/\1/')
if [[ $SRCNAME == "" ]]; then
    # most likely, passed as a path argument
    _dirname=$(dirname ${SRCREPO})
    SRCNAME=${_dirname##*/}
fi

DSTNAME=$(basename ${DSTREPO} | sed -e 's/\(.*\)\..*/\1/')
if [[ $DSTNAME == "" ]]; then
    # most likely, passed as a path argument
    _dirname=$(dirname ${DSTREPO})
    DSTNAME=${_dirname##*/}
fi

echo "Cloning source repository ${SRCREPO} into ${SRCNAME}"
git clone ${SRCREPO} ${SRCNAME}
cd ${SRCNAME}
SRCPATH=$(pwd)

SRCBRANCHES=$(git branch -r --no-color | ack -v HEAD | sed -e 's/\s*origin\/\(.*\)/\1/')
echo "Will merge branches: ${SRCBRANCHES}"
# checkout each branch so we have a local copy of it after removing 'origin'
for branch in $SRCBRANCHES; do
    git checkout ${branch}
done

echo "Removing 'origin'"
git remote remove origin

echo "Moving all content into ${BASENAME} subfolder"
NESTEDAT=""
if [[ ${BASENAME##*/} != ${BASENAME%/*} ]]; then
    # moving into a nested subfolder, need to create the path leading to it
    # before each move
    NESTEDAT=${BASENAME%/*}
fi
git filter-branch -f --prune-empty --tag-name-filter cat --tree-filter "mkdir -p .sub && mv * .sub && if [ -n \"${NESTEDAT}\" ]; then mkdir -p \"${NESTEDAT}\"; fi && mv .sub ${BASENAME}" -- --all

for branch in $SRCBRANCHES; do
    git checkout ${branch}
    if [[ -f .gitignore ]]; then
        echo "Moving .gitignore"
        git mv .gitignore ${BASENAME}
        git commit -m "moved .gitignore"
    fi
    if [[ -f .gitmodules ]]; then
        echo "Removing submodule directories"
        for module in $(git submodule status | cut -d ' ' -f 2); do
            echo "Removing $module"
            git rm -rf $module
        done
        git commit -m "removed submodule paths"
    fi
done

SKIPCHECKOUT=0
cd ..
if [[ -d ${DSTNAME} ]]; then
    echo "Destination repo exists at ${DSTNAME}"
    SKIPCHECKOUT=1
else
    echo "Cloning destination repository ${DSTREPO} into ${DSTNAME}"
    git clone ${DSTREPO} ${DSTNAME}
fi
cd ${DSTNAME}

if [[ $SKIPCHECKOUT == 0 ]]; then
    # try to checkout needed branches (and create those that do not exist)
    for branch in $SRCBRANCHES; do
        echo "Checking out branch ${branch}"
        if ! git checkout ${branch}; then
            echo "Branch ${branch} does not exist in ${SRCNAME}, creating"
            git checkout -b ${branch}
        fi
        # back to master before the next iteration
        git checkout master
    done
fi

echo "Removing 'origin'"
# just to be on the safe side, do this even if the repo was not cloned by us
git remote remove origin || true

echo "Adding local source repository as a remote"
git remote add merge-repo ${SRCPATH}/.git

echo "Fetching source repository's objects"
git remote update

echo "Merging source repository"
for branch in $SRCBRANCHES; do
    # Switch to the branch if it exists, create a new one if it doesn't
    echo "Merging branch ${branch}"
    git checkout ${branch}
    git merge -m "Merged branch ${branch} of ${SRCNAME}" -s recursive --strategy-option=ours merge-repo/${branch}
done

echo "Removing 'merge-repo' remote"
git remote remove merge-repo

git checkout master

if [[ ${PATCHFILE} != "" ]]; then
    echo "Patching..."
    git apply ../${PATCHFILE} || true
    echo "Check patch results, commit with 'git commit -am \"updated references to ${DSTNAME} location\"'"
fi

echo "Use 'git remote add origin ${SRCREPO}' to add the 'origin' remote back in ${SRCPATH}"

cd ..

For anyone using this couple of points that might assist:
Line 35 you could substitute grep for ack if you don't have ack installed
Line 110 later versions of git don't out of the box support the merging of unrelated histories. To solve add this flag to the merge command --allow-unrelated-histories

Usage is basically:
repo-merge-sh

Good script that works well