Fast forward merges one branch into another without having to checkout either - fails if the second parameter is not fast-forwardable.

git-merge-ff-only.sh

#!/bin/bash

# usage: 
# git-merge-ff-only.sh master develop
# Will only merge develop into master if its fast-forwardable.


merge_into=$1;
merge_from=$2;

git merge-base --is-ancestor $merge_into $merge_from;
is_ffable=$?

if [ $is_ffable == 0  ]; then
  git update-ref refs/heads/$merge_into $merge_from;
  echo "[$merge_from] has been fast-forward merged into [$merg_into]";
else
  echo "[$merge_from] can NOT be fast-forward merged into [$merged_into]";
fi