gistfile1.sh

#!/bin/bash
# subshell for `set -e` and `trap`
(
    set -e # fail immediately if there's a problem

    # use `git-up` if installed
    # if type git-up > /dev/null 2>&1
    # then
    #     exec git-up
    # fi

    # fetch upstream changes
    git fetch

    BRANCH=$(git describe --contains --all HEAD)
    if [ -z "$(git config branch.$BRANCH.remote)" -o -z "$(git config branch.$BRANCH.merge)" ]
    then
        echo "\"$BRANCH\" is not a tracking branch." >&2
        exit 1
    fi

    # create a temp file for capturing command output
    TEMPFILE="$(mktemp -t gup.XXXXXX)"
    trap '{ rm -f "$TEMPFILE"; }' EXIT

    # if we're behind upstream, we need to update
    if git status | grep "# Your branch" > "$TEMPFILE"
    then

        # extract tracking branch from message
        UPSTREAM=$(cat "$TEMPFILE" | cut -d "'" -f 2)
        if [ -z "$UPSTREAM" ]
        then
            echo Could not detect upstream branch >&2
            exit 1
        fi

        # can we fast-forward?
        CAN_FF=1
        grep -q "can be fast-forwarded" "$TEMPFILE" || CAN_FF=0

        # stash any uncommitted changes
        git stash | tee "$TEMPFILE"
        [ "${PIPESTATUS[0]}" -eq 0 ] || exit 1

        # take note if anything was stashed
        HAVE_STASH=0
        grep -q "No local changes" "$TEMPFILE" || HAVE_STASH=1

        if [ "$CAN_FF" -ne 0 ]
        then
            # if nothing has changed locally, just fast foward.
            git merge --ff "$UPSTREAM"
        else
            # rebase our changes on top of upstream, but keep any merges
            git rebase -p "$UPSTREAM"
        fi

        # restore any stashed changes
        if [ "$HAVE_STASH" -ne 0 ]
        then
            git stash pop -q
        fi

    fi

)