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.
#
# Adapted by Daniel Miller
# - allow changes to be saved back to the working copy when diffing against HEAD
# - work when FileMerge is already open
# - always compare archived copies so ignored files are excluded from the diff
#
# Known issues:
# - Always uses the same two directories (/tmp/git-opendiff-old and
#   /tmp/git-opendiff-new); THEY WILL BE DELETED IF THEY ALREADY EXIST.
#   Ugly, I know, but it makes the script work even if FileMerge is open.
# - Does not show unstaged changes.

if test $# = 0; then
    echo "usage: $0 (--cached | <ref>) [<ref>]"
    exit
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"

TMP_OLD=/tmp/git-opendiff-old
TMP_NEW=/tmp/git-opendiff-new
test -d $TMP_OLD && rm -rf $TMP_OLD; mkdir $TMP_OLD
test -d $TMP_NEW && rm -rf $TMP_NEW; mkdir $TMP_NEW

TMP_OLD=$TMP_OLD/$OLD; mkdir -p $TMP_OLD
git archive --format=tar $OLD | (cd $TMP_OLD; tar xf -)

if test -z "$NEW"; then
    SAVE_TO=$(git rev-parse --show-cdup)
    test -z "$cdup" && SAVE_TO=.
    git archive --format=tar HEAD | (cd $TMP_NEW; tar xf -)
    opendiff $TMP_OLD $TMP_NEW -merge $SAVE_TO
else
    TMP_NEW=$TMP_NEW/$NEW; mkdir -p $TMP_NEW
    git archive --format=tar $NEW | (cd $TMP_NEW; tar xf -)
    opendiff $TMP_OLD $TMP_NEW
fi