Re: Low-level repository inspection (Re: Where do I stick development documentation?)

From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Date: Aug 12, 2010, 03:40 UTC
Message-ID: <AANLkTikpT=PD0Q8d=6=989N6rxYXH-Le3Go_szAz-t4s@mail.gmail.com>
In-Reply-To: <20100812031756.GD19174@burratino>

On Thu, Aug 12, 2010 at 03:17, Jonathan Nieder <jrnieder@gmail.com> wrote:

Show 8 quoted lines

> Ævar Arnfjörð Bjarmason wrote:
>
>> It'd also be very neat if we had tools to print out any object in its
>> raw form, --pretty=raw is partly there, but it's more pretty than
>> raw.
>
> How about git cat-file (and other “interrogation commands” listed in
> git.1)?

Those are part of the way there, but you often have to tease info out of them, e.g. if you want a commit -> commit roundtrip:

    $ echo 7980e417 | git cat-file --batch | perl -0777 -pe 's/.*
commit ([0-9]*).(.*)\n/commit $1\0$2/s'|sha1sum
    7980e41746bc5de91eea775f9142ce44b1100361  -

The raw output from that is:

    $ echo 7980e417 | git cat-file --batch
    7980e41746bc5de91eea775f9142ce44b1100361 commit 525
    tree 782007df51255ab3793e528a4b5c4a69342166f2
    parent 0d0ba03a18a9c6cbc3d55c1b6834b9c3824f823f
    parent b5e233ecc411c8685463333d180a135c6866c50e
    author Junio C Hamano <gitster@pobox.com> 1281551520 -0700
    committer Junio C Hamano <gitster@pobox.com> 1281551520 -0700

    Merge branch 'maint'

    * maint:
      post-receive-email: remove spurious commas in email subject
      fast-import: export correctly marks larger than 2^20-1
      t/lib-git-svn.sh: use $PERL_PATH for perl, not perl from $PATH
      diff: strip extra "/" when stripping prefix

It'd be nice to answer "how are object stored" with something like:

    $ echo 7980e417 | git some-thing --pretty=raw -
    commit <SP> 525 <NULL>
    tree ....

And be able to do something similar to see what's stored in an arbitrary pack file, I've often wished I had something like that when using git-fsck.

These docs are also an excellent resource, afaict we only hint at something like this in git, e.g. in the git-cat-file(1) manpage: http://www-cs-students.stanford.edu/~blynn/gitmagic/ch08.html