git-ff

#!/bin/bash

# Attempts to fast-forward the current local branch to its remote tracked branch.
# Safely refuses if there is no remote tracking, or if a fast-forward is not possible.
# @author Paul Annesley

if [ -n "$(git merge --ff-only 2>&1 | grep 'unknown option')" ]; then
  echo "Your git doesn't seem to support --ff-only... try git 1.7+"
  exit 1
fi

local_ref=$(git symbolic-ref -q HEAD)
local_branch="${local_ref#refs/heads/}"

remote_ref=$(git config "branch.$local_branch.merge")
remote_branch="${remote_ref#refs/heads/}"

remote=$(git config "branch.$local_branch.remote")

if [ -z $remote_branch ] || [ -z $remote ]; then
  echo "Local branch '$local_branch' not tracked against a remote."
  exit 1
fi

git merge --ff-only ${remote}/${remote_branch}

This no longer works as of git 2.1:

"git merge" without an argument, even when there is an upstream defined for the current branch, refused to run until merge.defaultToUpstream is set to true. Flip the default of that configuration variable to true.

It's not worth fixing, because it can be replaced by an ff alias for merge --ff-only. That wasn't possible four year ago when this was written.