Provided by: git-man_1.9.1-1ubuntu0.10_all 
NAME
git-patch-id - Compute unique ID for a patch
SYNOPSIS
git patch-id < <patch>
DESCRIPTION
A "patch ID" is nothing but a SHA-1 of the diff associated with a patch, with whitespace and line numbers
ignored. As such, it’s "reasonably stable", but at the same time also reasonably unique, i.e., two
patches that have the same "patch ID" are almost guaranteed to be the same thing.
IOW, you can use this thing to look for likely duplicate commits.
When dealing with git diff-tree output, it takes advantage of the fact that the patch is prefixed with
the object name of the commit, and outputs two 40-byte hexadecimal strings. The first string is the patch
ID, and the second string is the commit ID. This can be used to make a mapping from patch ID to commit
ID.
OPTIONS
<patch>
The diff to create the ID of.
GIT
Part of the git(1) suite