From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jonathan Nieder <jrnieder@gmail.com>
Subject: Re: How git detects changes during commit?
Date: Wed, 27 Oct 2010 15:54:41 -0500
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To: longphant <longphant@yahoo.com>
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Hi,

longphant wrote:

> Say you check out a directory of 100 files. You edit 5 of the files, and you
> go to commit the directory back. How does git know which of the 100 files
> were modified (not all of them were)?

The lstat system call.  See the git-update-index(1) manual for some
hints (since most high-level commands do the equivalent of
"git update-index --refresh -q" before working with the work tree).

Hope that helps,
Jonathan