Using Filemerge.app as a git-diff viewer

Mac OS X bundles a rather nice graphical diff viewer (Filemerge.app) with its developer tools.

While git-merge knows how to use this as a merge tool, I couldn't find any way to easily use Filemerge as a viewer for the output of git-diff.

(http://thread.gmane.org/gmane.comp.version-control.git/58702 discusses the problem, and recommends piping git-diff into kompare. Filemerge unfortunately won't accept diff output on stdin)

So I wrote a quick script (below) which does what I need. Of all the available git-diff flags, it only understands "--cached", and up to two commit objects, and no paths, but that's enough for me. Within those constraints, it has the same semantics as git-diff.

It's not very nice, but in case anyone else wants this:

#!/bin/sh # # 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`
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