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From: "brian m. carlson" <sandals@crustytoothpaste.net>
To: Chris Torek <chris.torek@gmail.com>
Cc: Taylor Blau <me@ttaylorr.com>, Denton Liu <liu.denton@gmail.com>,
	Git Mailing List <git@vger.kernel.org>
Subject: Re: [PATCH 2/4] builtin/rev-parse: learn --null-oid
Date: Sun, 20 Sep 2020 18:58:17 +0000	[thread overview]
Message-ID: <20200920185817.GJ67496@camp.crustytoothpaste.net> (raw)
In-Reply-To: <CAPx1Gvd6vcvM410wZUZygr4-2Ob6gaScF3DnBtWWsT95XDmKSQ@mail.gmail.com>

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On 2020-09-20 at 04:25:33, Chris Torek wrote:
> On Fri, Sep 18, 2020 at 2:34 PM brian m. carlson
> <sandals@crustytoothpaste.net> wrote:
> > 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).

If we're looking for best compatibility here, then using egrep and
/dev/null is best, I agree.  I personally use the POSIX version because
it's been that way since at least 2001 and I don't have a problem with
requiring compliance with a 19-year-old standard.  But for Git, we
should definitely do whatever we do in the testsuite if we use this
approach, since presumably that works everywhere.

As Andreas pointed out, there are ways to avoid the external process
that we could stuff in a shell function.  I'm not picky.

> > 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...?

I believe all modern versions of Git for Windows provide /dev/null via
the shell, since it's required for a lot of things to work, so I'm not
worried about this case.  It is definitely good to think about Windows,
though.
-- 
brian m. carlson: Houston, Texas, US

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  reply	other threads:[~2020-09-20 18:58 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-18 11:19 [PATCH 0/4] sample hooks: become hash agnostic Denton Liu
2020-09-18 11:19 ` [PATCH 1/4] hooks--pre-push.sample: prefer $() for command substitution Denton Liu
2020-09-18 16:57   ` Eric Sunshine
2020-09-18 11:19 ` [PATCH 2/4] builtin/rev-parse: learn --null-oid Denton Liu
2020-09-18 14:11   ` Taylor Blau
2020-09-18 14:16     ` Taylor Blau
2020-09-18 18:16       ` Junio C Hamano
2020-09-18 18:21         ` Taylor Blau
2020-09-18 21:26     ` brian m. carlson
2020-09-20  4:25       ` Chris Torek
2020-09-20 18:58         ` brian m. carlson [this message]
2020-09-20 15:35       ` Taylor Blau
2020-09-20 16:03       ` Andreas Schwab
2020-09-18 11:19 ` [PATCH 3/4] hooks--pre-push.sample: use hash-agnostic null OID Denton Liu
2020-09-18 17:06   ` Eric Sunshine
2020-09-18 11:19 ` [PATCH 4/4] hooks--update.sample: " Denton Liu
2020-09-18 17:08   ` Eric Sunshine
2020-09-18 21:35 ` [PATCH 0/4] sample hooks: become hash agnostic brian m. carlson
2020-09-23  9:38 ` [PATCH v2 0/3] " Denton Liu
2020-09-23  9:38   ` [PATCH v2 1/3] hooks--pre-push.sample: modernize script Denton Liu
2020-09-23  9:38   ` [PATCH v2 2/3] hooks--pre-push.sample: use hash-agnostic zero OID Denton Liu
2020-09-23  9:38   ` [PATCH v2 3/3] hooks--update.sample: " Denton Liu
2020-09-23 16:34   ` [PATCH v2 0/3] sample hooks: become hash agnostic Junio C Hamano

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