git-submodule-track

#!/bin/sh

root=`git rev-parse --show-toplevel`
echo=/bin/echo

git ls-files --stage | grep '^160000 ' |
while read mode sha1 stage path
do
    $echo -n "Submodule path '$path': ";

    cd $root; cd $path

    track_branch=`git config --file $root/.gitmodules submodule.$path.track`
    if [ -z "$track_branch" ]; then
        $echo 'tracking branch not found; skip.'
    else
        $echo -n "track $track_branch... "
        current_branch=`git symbolic-ref --quiet HEAD | sed 's#^refs/heads/##'`
        local_branch=${track_branch#*/}

        if [ "$current_branch" = "$local_branch" ]; then
            $echo "already on $current_branch."
            git pull
        else
            if git rev-parse --quiet --verify $local_branch > /dev/null; then
                $echo "checkout existing branch $local_branch."
                git checkout $local_branch && git pull
            else
                $echo "start tracking $track_branch."
                git fetch && git checkout --track $track_branch
            fi
        fi
    fi
done