Re: [PATCH 2/4] builtin/rev-parse: learn --null-oid

From: Chris Torek <chris.torek@gmail.com>
Date: Sep 20, 2020, 04:25 UTC
Message-ID: <CAPx1Gvd6vcvM410wZUZygr4-2Ob6gaScF3DnBtWWsT95XDmKSQ@mail.gmail.com>
In-Reply-To: <20200918212609.GC67496@camp.crustytoothpaste.net>

On Fri, Sep 18, 2020 at 2:34 PM brian m. carlson <sandals@crustytoothpaste.net> wrote:

> So I definitely want to distinguish between the null (all-zeros) OID and
> the OID of an empty object, and I think using "null" and "empty" are
> fine.

(I like this myself)

Show 11 quoted lines

> What I typically do when I write shell scripts, and which may obviate
> the need for this patch is turn this:
>
>   [ "$oid" = 0000000000000000000000000000000000000000 ]
>
> into this:
>
>   echo "$oid" | grep -qsE '^0+$'
>
> This is slightly less efficient, but it's also backwards compatible
> with older Git version assuming you have a POSIX grep.

Note that a lot of `grep`s do not have `-q` and/or `-s` so the portable variant of this is `grep '^0+$' >/dev/null` (you only need the `2>&1` part if you're concerned about bad input files or an error on a pipe or something).

Show 7 quoted lines

> I'm not sure we need an empty tree and empty blob object, because it's
> pretty easy to write these:
>
>   git hash-object -t tree /dev/null
>   git hash-object -t blob /dev/null
>
> That's what I've done in some of the transition code at least.

That's what's recommended in my 2012 stackoverflow Q&A, too. The use of `/dev/null` directly here is perhaps unsatisfactory on old Windows systems, though...?

Chris