From: Jeff King <peff@peff.net>
Date: Sun, 17 Aug 2025 01:50:13 GMT
Subject: Re: How To See Index File Checksum?
Message-ID: <20250817015013.GA6012@coredump.intra.peff.net>
In-Reply-To: <76ee89b3-39cf-4218-bbb6-1cc3c6e16ddf@gmail.com>

On Sat, Aug 16, 2025 at 06:32:30PM -0700, Jon Forrest wrote:

> I know how to see the checksums of the files in an index
> file. But, I can't find a git command that shows the
> checksum at the end of an index file.

I don't think that there's a command to do so (likewise for other
checksum'd files like pack idx, etc). We'd usually check those during
fsck but I don't know of any specific command to print them. I'd usually
do something like:

   fn=.git/index
   size=$(stat --format=%s $fn)
   # offset of hash; use 32 in a sha256 repo!
   hash=$((size - 20))
   # the computed hash
   dd if=$fn bs=1 count=$hash | sha1sum
   # what the file records
   dd if=$fn bs=1 skip=$hash | od -A none -t x1 | tr -d ' \n'

Which admittedly is kind of horrible, but this isn't generally needed
much outside of debugging.

-Peff