How do you merge two Git repositories?

Question

Consider the following scenario:

I have developed a small experimental project A in its own Git repo. It has now matured, and I'd like A to be part of larger project B, which has its own big repository. I'd now like to add A as a subdirectory of B.

How do I merge A into B, without losing history on any side?

Answer 1

I know it's long after the fact, but I wasn't happy with the other answers I found here, so I wrote this:

me=$(basename $0)

TMP=$(mktemp -d /tmp/$me.XXXXXXXX)
echo 
echo "building new repo in $TMP"
echo
sleep 1

set -e

cd $TMP
mkdir new-repo
cd new-repo
    git init
    cd ..

x=0
while [ -n "$1" ]; do
    repo="$1"; shift
    git clone "$repo"
    dirname=$(basename $repo | sed -e 's/\s/-/g')
    if [[ $dirname =~ ^git:.*\.git$ ]]; then
        dirname=$(echo $dirname | sed s/.git$//)
    fi

    cd $dirname
        git remote rm origin
        git filter-branch --tree-filter \
            "(mkdir -p $dirname; find . -maxdepth 1 ! -name . ! -name .git ! -name $dirname -exec mv {} $dirname/ \;)"
        cd ..

    cd new-repo
        git pull --no-commit ../$dirname
        [ $x -gt 0 ] && git commit -m "merge made by $me"
        cd ..

    x=$(( x + 1 ))
done

Answer 2

If you're trying to simply glue two repositories together, submodules and subtree merges are the wrong tool to use because they don't preserve all of the file history (as people have noted on other answers). See this answer here for the simple and correct way to do this.

Answer 3

This function will clone remote repo into local repo dir, after merging all commits will be saved, git log will be show the original commits and proper paths:

function git-add-repo
{
    repo="$1"
    dir="$(echo "$2" | sed 's/\/$//')"
    path="$(pwd)"

    tmp="$(mktemp -d)"
    remote="$(echo "$tmp" | sed 's/\///g'| sed 's/\./_/g')"

    git clone "$repo" "$tmp"
    cd "$tmp"

    git filter-branch --index-filter '
        git ls-files -s |
        sed "s,\t,&'"$dir"'/," |
        GIT_INDEX_FILE="$GIT_INDEX_FILE.new" git update-index --index-info &&
        mv "$GIT_INDEX_FILE.new" "$GIT_INDEX_FILE"
    ' HEAD

    cd "$path"
    git remote add -f "$remote" "file://$tmp/.git"
    git pull "$remote/master"
    git merge --allow-unrelated-histories -m "Merge repo $repo into master" --edit "$remote/master"
    git remote remove "$remote"
    rm -rf "$tmp"
}

How to use:

cd current/package
git-add-repo https://github.com/example/example dir/to/save

If make a little changes you can even move files/dirs of merged repo into different paths, for example:

repo="https://github.com/example/example"
path="$(pwd)"

tmp="$(mktemp -d)"
remote="$(echo "$tmp" | sed 's/\///g' | sed 's/\./_/g')"

git clone "$repo" "$tmp"
cd "$tmp"

GIT_ADD_STORED=""

function git-mv-store
{
    from="$(echo "$1" | sed 's/\./\\./')"
    to="$(echo "$2" | sed 's/\./\\./')"

    GIT_ADD_STORED+='s,\t'"$from"',\t'"$to"',;'
}

# NOTICE! This paths used for example! Use yours instead!
git-mv-store 'public/index.php' 'public/admin.php'
git-mv-store 'public/data' 'public/x/_data'
git-mv-store 'public/.htaccess' '.htaccess'
git-mv-store 'core/config' 'config/config'
git-mv-store 'core/defines.php' 'defines/defines.php'
git-mv-store 'README.md' 'doc/README.md'
git-mv-store '.gitignore' 'unneeded/.gitignore'

git filter-branch --index-filter '
    git ls-files -s |
    sed "'"$GIT_ADD_STORED"'" |
    GIT_INDEX_FILE="$GIT_INDEX_FILE.new" git update-index --index-info &&
    mv "$GIT_INDEX_FILE.new" "$GIT_INDEX_FILE"
' HEAD

GIT_ADD_STORED=""

cd "$path"
git remote add -f "$remote" "file://$tmp/.git"
git pull "$remote/master"
git merge --allow-unrelated-histories -m "Merge repo $repo into master" --edit "$remote/master"
git remote remove "$remote"
rm -rf "$tmp"

Notices
Paths replaces via sed, so make sure it moved in proper paths after merging.
The --allow-unrelated-histories parameter only exists since git >= 2.9.

Answer 4

I had a similar challenge, but in my case, we had developed one version of the codebase in repo A, then cloned that into a new repo, repo B, for the new version of the product. After fixing some bugs in repo A, we needed to FI the changes into repo B. Ended up doing the following:

1. Adding a remote to repo B that pointed to repo A (git remote add...)
2. Pulling the current branch (we were not using master for bug fixes) (git pull remoteForRepoA bugFixBranch)
3. Pushing merges to github

Worked a treat :)

Answer 5

If you want to merge project-a into project-b:

cd path/to/project-b
git remote add project-a path/to/project-a
git fetch project-a --tags
git merge --allow-unrelated-histories project-a/master # or whichever branch you want to merge
git remote remove project-a

Taken from: git merge different repositories?

This method worked pretty well for me, it's shorter and in my opinion a lot cleaner.

Note: The --allow-unrelated-histories parameter only exists since git >= 2.9. See Git - git merge Documentation / --allow-unrelated-histories

Update: Added --tags as suggested by @jstadler in order to keep tags.

Answer 6

I merge projects slightly manually, which allows me to avoid needing to deal with merge conflicts.

first, copy in the files from the other project however you want them.

cp -R myotherproject newdirectory
git add newdirectory

next pull in the history

git fetch path_or_url_to_other_repo

tell git to merge in the history of last fetched thing

echo 'FETCH_HEAD' > .git/MERGE_HEAD

now commit however you normally would commit

git commit