Use FileMerge as git difftool on Mac OS X

gdiff

#!/bin/bash
#
# A git difftool for Mac OS X that uses FileMerge from XCode
#
# source:  https://gist.github.com/gwarnes-mdsol/b0aff96fbb7a4c92e570e7b03daa7e1b
#
# Setup:
#
# 1. Copy this file to a known path, e.g. $HOME/bin/gdiff
# 2. Make the file executable:
#      chmod +x $HOME/bin/gdiff
# 2. Tell git to use this script as the preferred difftool:
#      git config --global diff.tool $HOME/bin/gdiff
#
# Usage:
#
#   git difftool <git diff arguments>
#

# find top level of git project
dir=$PWD
until [ -e "$dir/.git" ]; do
  if [ "$dir" == "/" ]; then
    echo "Not a git repository" >&2
    exit 1;
  fi
  dir=`dirname "$dir"`
done

# open fresh FileMerge and wait for terminations to issues with git temp files
open -a FileMerge -n -W --args -left "$1" -right "$2" -merge "$dir" ${@:2}

# references:
# http://hints.macworld.com/article.php?story=20070220223441729
# https://gist.github.com/bkeating/329690
# https://gist.github.com/miner/e73fc98a83a8fe05d9ef000d46d68a9f

This version adds support for passing additional command line arguments, such as a branch specification:

git difftool -d origin/master

and provides information on how to configure it to be used by default.