git-ffwd

#!/bin/bash
SUBDIRECTORY_OK=1 source "$(git --exec-path)/git-sh-setup" ||
    die "Not a git repository."


has_matching_push() {
    # push.default is setup for 'simple', 'current', or 'matching'.
    case "$(git config --get push.default || echo "matching")" in
        current | simple | matching)
            return 0
    esac

    return 1
}


if has_matching_push; then
    MATCHING_PUSH=t
else
    MATCHING_PUSH=
fi


determine_upstream_branch() {
    local ref="${1#refs/heads/}"
    local upstream="$(git for-each-ref --format='%(upstream:short)' "refs/heads/$ref")"
    local publish_branch

    if [[ -n "$upstream" ]]; then
        echo "$upstream"
        return 0
    fi

    if [[ -z "$MATCHING_PUSH" ]]; then
        return 1
    fi

    # Use the push location as the upstream.
    local remote=$(git config --get branch.${ref}.pushremote ||
        git config --get remote.pushdefault ||
        git config --get branch.${ref}.remote)
    if [ -z "$remote" -a -n "$(git config --get remote.origin.url 2> /dev/null)" ]; then
        remote="origin"
    fi
    if [[ -n "$remote" ]]; then
        git rev-parse "$remote/$ref" > /dev/null 2>&1 &&
            publish_branch="$remote/$ref"
    fi

    if [[ -n "$publish_branch" ]]; then
        echo "$publish_branch"
        return 0
    fi

    return 1
}


# Taken from http://stackoverflow.com/questions/620650/can-i-easily-update-all-local-git-branches-from-remote-branches-simultaneously/answer-9076361
# with a small tweak by me to make the fast-forward merge use --ff-only, and to
# help prune remote branches.  It has also been updated to treat the push branch
# as the default upstream, if no upstream is configured.
main() {
    local upstream
    local ALR
    local LR

    local CLB=$(git branch -l|awk '/^\*/{print $2}')

    local REMOTES="$@"
    if [ -z "$REMOTES" ]; then
        REMOTES="$(git remote)"
    fi
    REMOTES="$(echo "$REMOTES" | xargs -n1 echo)"

    git remote update -p $REMOTE
    git show-ref --heads | cut -d ' ' -f 2 | while read ALB; do
        LB="${ALB#refs/heads/}"
        RB="$(determine_upstream_branch "${LB}")"
        if [ -z "${RB}" ]; then
            continue
        fi

        NBEHIND=$(( $(git rev-list --count $LB..$RB 2>/dev/null) +0))
        NAHEAD=$(( $(git rev-list --count $RB..$LB 2>/dev/null) +0))

        if [ "$NBEHIND" -gt 0 ]; then
            if [ "$NAHEAD" -gt 0 ]; then
                echo " branch $LB is $NBEHIND commit(s) behind and $NAHEAD commit(s) ahead of $RB. could not be fast-forwarded"
            elif [ "$LB" = "$CLB" ]; then
                echo " branch $LB was $NBEHIND commit(s) behind $RB. fast-forward merge";
                git merge --ff --ff-only -q $RB
            else
                echo " branch $LB was $NBEHIND commit(s) behind $RB. resetting local branch to remote"
                git branch -l -f $LB -t $RB >/dev/null
            fi
        fi
    done
}

main $@