Moves commits from one repo to another preserving commit messages and author date.

git-move.sh

# Usage:
#    cd ~/my_old_repo
#    git-move HEAD ~/my_new_repo

function git-move {
    src=$(pwd)
    commit=$1
    dest=$2
    git rev-list $commit --reverse |
    while read hash; do
        date=$(git log -1 $hash --pretty=format:%ad)
        git archive $hash |
        (cd $dest &&
            tar -xpf - &&
            git add --all &&
            cat <(cd $src && git log -1 $hash --pretty=format:%s) |
            git commit --date="$date" -F -)
    done
}