is there a reason pre-commit.sample uses "git diff-index"?

From: Robert P. J. Day <rpjday@crashcourse.ca>
Date: May 31, 2018, 16:38 UTC
Message-ID: <alpine.LFD.2.21.1805311235410.15130@localhost.localdomain>

  was going over some hooks and writing some tutorials for some of the
commit-related, client-side hooks, and was wondering (perhaps
stupidly) why the pre-commit.sample hook uses, as its last line:

  exec git diff-index --check --cached $against --
           ^^^^^^^^^^

as in, could this not be done equivalently with just git diff, not git diff-index? i just did a quick test and it seems to do the same thing, but i've never taken a close look at git diff-index before so i may just be clueless about some important distinction.

rday

-- 
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Robert P. J. Day                                 Ottawa, Ontario, CANADA
                  http://crashcourse.ca/dokuwiki

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