Re: strange behavior of git diff-index

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

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Hi Oussama,

On Wed, 22 May 2019, Oussama Ghorbel wrote:

> git diff-index is giving me incorrect information, however if I run git diff, then git diff-index again it will show the correct information.
> The steps are the following:
> $ git diff-index --name-only HEAD
> git appears to list all files in the project irrespective if they modified or not
> $ git diff
> $ git diff --cached
> will show nothing. So I don't have any modification. 
> Now strangely if I run git diff-index, it will also show nothing which is correction behavior.
>
> my git version is 2.7.4
> Any explanation?

The low-level `diff-index` command is meant to be used in scripts, and
does specifically *not* refresh the index before running. Meaning that it
could possibly mistake a file for being modified even if it is not
modified, just because it is marked "modified" in the index [*1*].

Short answer: use the high-level command `git diff` that is intended for
human consumption.

Ciao,
Johannes

Footnote *1*: It is actually a bit more complicated than that: the index
stores metadata such as mtime, size, uid, etc, and compares that to the
metadata on disk. If there is any mismatch, or if everything matches but
the mtime *also* matches the index file's itself, the file is considered
not up to date, i.e. marked as modified.