fast-forward local tracking branch

git-ff-track

#!/bin/bash
# fast-forward local tracking branch if you get something like (on git checkout):
# Your branch is behind 'origin/master' by 1 commit, and can be fast-forwarded.
# Author: Valentin Haenel <valentin.haenel@gmx.de>
# Licence: wtfpl <http://sam.zoy.org/wtfpl/>

BRANCH=$( git branch | grep ^* | sed 's/^\* //' )
if [[ -z $BRANCH ]] ; then
    # not a git repository
    exit 1
elif [[ $BRANCH == '(no branch)' ]] ; then
    echo 'You have a detached HEAD.'
    exit 2
fi
REMOTE=$( git config branch.$BRANCH.remote )
if [[ -n $BRANCH && -z $REMOTE ]] ; then
    echo "Your branch '$BRANCH' isn't tracking anything."
    exit 3
elif [[ -n $REMOTE && -n $( git config branch.$BRANCH.merge) ]] ; then
    remote_ahead_local=$( git log --oneline $BRANCH..$REMOTE/$BRANCH)
    local_ahead_remote=$( git log --oneline $REMOTE/$BRANCH..$BRANCH)
    if [[ -z $remote_ahead_local && -z $local_ahead_remote ]] ; then
            if [[ $( git rev-parse $BRANCH )  == $( git rev-parse $REMOTE/$BRANCH ) ]] ; then
                echo "Your branch '$BRANCH' points to same commit as '$REMOTE/$BRANCH', doing nothing."
                exit 4
            else
                echo "Dude..."
                exit 42
            fi  
    fi  
    if [[ -z $remote_ahead_local && -n $local_ahead_remote ]] ; then
        echo "Your branch '$BRANCH'is ahead of '$REMOTE/$BRANCH', perhaps you want to push?"
        exit 5
    fi  
    if [[ -n $local_ahead_remote && -n $remote_ahead_local ]] ; then
        echo "Your branches '$BRANCH' and '$REMOTE/$BRANCH' and have diverged, fast-forward not possible!"
        exit 6
    fi  
    if [[ -n $remote_ahead_local && -z $local_ahead_remote ]] ; then
        echo "Fast-forward '$BRANCH' to '$REMOTE/$BRANCH'."
        git merge --ff-only $REMOTE/$BRANCH
        exit 0
    fi  
fi