Automatically fetch remotes then fast forward to the new changes or launch a GUI.

ff_branches.sh

# first update all remote branches
git fetch --all --prune

# loop over all local/remote pairs
git for-each-ref --format="%(refname:short) %(upstream:short)" refs/heads | \
while read local remote
do
    # make sure remote exists
    [ -z "$remote" ] && continue

    # see if there is a difference between the two
    if [ -n "$(git rev-list --left-right ${local}..${remote})" ]
    then
        # if there is attempt a fast forward merge
        git checkout $local
        git merge --ff-only $remote
    fi

    # finally if the ff-merge failed launch a gui to view the branches
    if [ -n "$(git rev-list --left-right ${local}..${remote})" ]
    then
        $(which gitx || which gitg || which gitk || which git gui)
        continue
    fi
done