+# Copyright 2010 - 2012, Tim Henigan <tim.henigan@gmail.com>
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be included
+# in all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+# OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+# IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+# CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+# TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+
+# Perform a directory diff between commits in the repository using
+# the external diff or merge tool specified in the user's config.
+
+USAGE='[--cached] [--copy-back] [-x|--extcmd=<command>] <commit>{0,2} [-- <path>*]
+
+ --cached Compare to the index rather than the working tree.
+
+ --copy-back Copy files back to the working tree when the diff
+ tool exits (in case they were modified by the
+ user). This option is only valid if the diff
+ compared with the working tree.
+
+ -x=<command>
+ --extcmd=<command> Specify a custom command for viewing diffs.
+ git-diffall ignores the configured defaults and
+ runs $command $LOCAL $REMOTE when this option is
+ specified. Additionally, $BASE is set in the
+ environment.
+'