Rewrite history git filter-branch create / split into submodules / subprojects

I resolved my own question, here is the solution:

git-submodule-split library another_library

Script git-submodule-split:

    #!/bin/bash

    set -eu

    if [ $# -eq 0 ]
    then
        echo "Usage: $0 submodules-to-split"
    fi

    export _tmp=$(mktemp -d)
    export _libs="$@"
    for i in $_libs
    do
        mkdir -p $_tmp/$i
    done

    git filter-branch --commit-filter '
    function gitCommit()
    {
        git add -A
        if [ -n "$(git diff --cached --name-only)" ]
        then
            git commit -F $_msg
        fi
    } >/dev/null

    # from git-filter-branch
    git checkout-index -f -u -a || die "Could not checkout the index"
    # files that $commit removed are now still in the working tree;
    # remove them, else they would be added again
    git clean -d -q -f -x

    _git_dir=$GIT_DIR
    _git_work_tree=$GIT_WORK_TREE
    _git_index_file=$GIT_INDEX_FILE
    unset GIT_DIR
    unset GIT_WORK_TREE
    unset GIT_INDEX_FILE

    _msg=$(tempfile)
    cat /dev/stdin > $_msg
    for i in $_libs
    do
        if [ -d "$i" ]
        then
            unset GIT_DIR
            unset GIT_WORK_TREE
            unset GIT_INDEX_FILE
            cd $i
            if [ -d ".git" ]
            then
                gitCommit
            else
                git init >/dev/null
                gitCommit
            fi
            cd ..
            rsync -a -rtu $i/.git/ $_tmp/$i/.git/
            export GIT_DIR=$_git_dir
            export GIT_WORK_TREE=$_git_work_tree
            export GIT_INDEX_FILE=$_git_index_file
            git rm -q -r --cached $i
            git submodule add ./$i >/dev/null
            git add $i
        fi
    done
    rm $_msg
    export GIT_DIR=$_git_dir
    export GIT_WORK_TREE=$_git_work_tree
    export GIT_INDEX_FILE=$_git_index_file

    if [ -f ".gitmodules" ]
    then
        git add .gitmodules
    fi

    _new_rev=$(git write-tree)
    shift
    git commit-tree "$_new_rev" "$@";
    ' --tag-name-filter cat -- --all

    for i in $_libs
    do
        if [ -d "$_tmp/$i/.git" ]
        then
            rsync -a -i -rtu $_tmp/$i/.git/ $i/.git/
            cd $i
            git reset --hard
            cd ..
        fi
    done
    rm -r $_tmp

    git for-each-ref refs/original --format="%(refname)" | while read i; do git update-ref -d $i; done

    git reflog expire --expire=now --all
    git gc --aggressive --prune=now