tj.git-extras/bin/git-merge-into

#!/usr/bin/env bash

current_branch() {
    git rev-parse --abbrev-ref HEAD
}

usage() {
    echo "Usage: git merge-into [src] dest [--ff-only]"
}

cur_branch=$(current_branch)

stashed=0
if [ -n "$(git status --porcelain)" ];
then
    echo "Local modifications detected, stashing"
    stashed=1
    git stash
fi

if [ "${!#}" == '--ff-only' ]; then
    case $# in
        2 ) # dest --ff
            git push "$(git rev-parse --show-toplevel)" "$cur_branch":"$1";;
        3 )
            git push "$(git rev-parse --show-toplevel)" "$1":"$2";;
        * )
            usage
    esac
else
    case $# in
        1 )
            git checkout "$1"
            git merge "$cur_branch" "$1" && git checkout "$cur_branch"
            ;;
        2 )
            git checkout "$2"
            git merge "$1" "$2" && git checkout "$cur_branch"
            ;;
        * )
            usage
    esac
fi

if [ $stashed -eq 1 ];
then
    git stash pop;
fi