git-opendiff

#!/bin/sh
#
# This script was written by Toby White under an unknown license, and published
# on the Git mailing list:
#
#   http://kerneltrap.org/mailarchive/git/2007/11/21/435536
#
# Superficial changes were made by Nathan de Vries to allow the script to be 
# run under Leopard. Tony's original instructions follow:
#
# Filemerge.app must not already be open before running this script, or opendiff
# below will return immediately, and the TMPDIRs deleted before it gets the 
# chance to read them.

if test $# = 0; then
   OLD=`git write-tree`
elif test "$1" = --cached; then
   OLD=HEAD
   NEW=`git write-tree`
   shift
fi
if test $# -gt 0; then
   OLD="$1"; shift
fi
test $# -gt 0 && test -z "$CACHED" && NEW="$1"

TMPDIR1=`mktemp -d /tmp/opendiff.XXXX`
git archive --format=tar $OLD | (cd $TMPDIR1; tar xf -)
if test -z "$NEW"; then
   TMPDIR2=$(git rev-parse --show-cdup)
   test -z "$cdup" && TMPDIR2=.
else
   TMPDIR2=`mktemp -d`
   git archive --format=tar $NEW | (cd $TMPDIR2; tar xf -)
fi

opendiff $TMPDIR1 $TMPDIR2 | cat
rm -rf $TMPDIR1
test ! -z "$NEW" && rm -rf $TMPDIR2