$ git format-patch --attach --stdout --suffix=.diff initial..side
From c7a2ab9e8eac7b117442a607d5a9b3950ae34d5a Mon Sep 17 00:00:00 2001
From: A U Thor <author@example.com>
Date: Mon, 26 Jun 2006 00:03:00 +0000
Subject: [PATCH] Side
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="------------g-i-t--v-e-r-s-i-o-n"

This is a multi-part message in MIME format.
--------------g-i-t--v-e-r-s-i-o-n
Content-Type: text/plain; charset=UTF-8; format=fixed
Content-Transfer-Encoding: 8bit

---
 dir/sub | 2 ++
 file0   | 3 +++
 file3   | 4 ++++
 3 files changed, 9 insertions(+)
 create mode 100644 file3


--------------g-i-t--v-e-r-s-i-o-n
Content-Type: text/x-patch; name="0001-Side.diff"
Content-Transfer-Encoding: 8bit
Content-Disposition: attachment; filename="0001-Side.diff"

diff --git a/dir/sub b/dir/sub
index 35d242b..7289e35 100644
--- a/dir/sub
+++ b/dir/sub
@@ -1,2 +1,4 @@
 A
 B
+1
+2
diff --git a/file0 b/file0
index 01e79c3..f4615da 100644
--- a/file0
+++ b/file0
@@ -1,3 +1,6 @@
 1
 2
 3
+A
+B
+C
diff --git a/file3 b/file3
new file mode 100644
index 0000000..7289e35
--- /dev/null
+++ b/file3
@@ -0,0 +1,4 @@
+A
+B
+1
+2

--------------g-i-t--v-e-r-s-i-o-n--


$