From: Jeff King <peff@peff.net>
To: Junio C Hamano <gitster@pobox.com>
Cc: Eric Rannaud <eric.rannaud@gmail.com>,
git@vger.kernel.org,
Johannes Schindelin <johannes.schindelin@gmx.de>,
Jeremy Serror <jeremy.serror@gmail.com>
Subject: Re: git rebase regression: cannot pass a shell expression directly to --exec
Date: Mon, 15 May 2017 23:53:58 -0400 [thread overview]
Message-ID: <20170516035357.2wutcd2tyax4tjyn@sigill.intra.peff.net> (raw)
In-Reply-To: <xmqqr2zp31vg.fsf@gitster.mtv.corp.google.com>
On Tue, May 16, 2017 at 12:40:51PM +0900, Junio C Hamano wrote:
> Jeff King <peff@peff.net> writes:
>
> > Interesting. The "exec" string is still run with a shell. E.g.:
> > ...
> > I wonder if this is falling afoul of the optimization in run-command's
> > prepare_shell_cmd() to skip shell invocations for "simple" commands.
> > ...
> > So I suspect if you added an extraneous semi-colon, your case would work
> > again (and that would confirm for us that this is indeed the problem).
>
> Wow, that's a brilliant analysis.
If it's right. :) It's all theory at this point.
My /bin/sh isn't bash, but I should be able to build with
SHELL_PATH=/bin/bash to reproduce. But I can't:
$ bash
$ foo() { echo >&2 "in foo"; }
$ export -f foo
$ bash -c foo
in foo
$ strace -f 2>&1 git.compile rebase -x 'foo;' HEAD^ | grep foo
Executing: foo;
[pid 1788] execve("/bin/bash", ["/bin/bash", "-c", "foo;", "foo;"], [/* 60 vars */] <unfinished ...>
foo;: foo: command not found
So I'm not sure why the direct "bash -c" can find it, but somehow the
variable doesn't make it through to the "bash -c" at the lower level.
Replacing "foo;" with "env" shows the environment, but BASH_FUNC_foo
isn't set in it. I'm not sure where it's getting eaten, though.
> The "semicolon" trick is way too obscure, but perhaps can be
> documented as an escape hatch?
Yeah, I agree this should be documented if it can't be fixed. I wasn't
sure if we were giving up just yet.
Either way, though, it wouldn't hurt to mention optimizing out "maybe
shell" optimization, because it can occasionally produce user-visible
effects. Where would be a good place? In git(1), I guess?
It's almost something that could go in gitcli(7), but it's not really
about the CLI in particular. In most cases the shell-exec'd commands are
from config, but not always (as this case shows). So git-config(1)
probably isn't the right place.
AFAIK, we don't talk about this behavior at all in the existing
documentation. And I really don't know where we'd put it that somebody
would find it without having to read the documentation exhaustively.
-Peff
next prev parent reply other threads:[~2017-05-16 3:54 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-15 18:08 git rebase regression: cannot pass a shell expression directly to --exec Eric Rannaud
2017-05-16 3:25 ` Jeff King
2017-05-16 3:37 ` Jeff King
2017-05-16 16:41 ` Jonathan Nieder
2017-05-16 16:47 ` Jeff King
2017-05-16 17:11 ` Eric Rannaud
2017-05-16 17:15 ` Brandon Williams
2017-05-16 17:23 ` Jeff King
2017-05-16 17:30 ` Brandon Williams
2017-05-16 19:14 ` Linus Torvalds
2017-05-16 19:35 ` [TANGENT] run-command: use vfork instead of fork Eric Wong
2017-05-16 20:47 ` Linus Torvalds
2017-05-16 21:11 ` Brandon Williams
2017-05-16 20:12 ` git rebase regression: cannot pass a shell expression directly to --exec Johannes Schindelin
2017-05-16 20:27 ` Linus Torvalds
2017-05-16 17:37 ` Jonathan Nieder
2017-05-16 3:40 ` Junio C Hamano
2017-05-16 3:53 ` Jeff King [this message]
2017-05-16 4:08 ` Jeff King
2017-05-16 16:45 ` Eric Rannaud
2017-05-16 10:46 ` Johannes Schindelin
2017-05-16 10:23 ` Johannes Schindelin
2017-05-16 16:18 ` Jeff King
2017-05-16 16:59 ` Eric Rannaud
2017-05-16 17:14 ` Kevin Daudt
2017-05-16 17:29 ` Eric Rannaud
2017-05-16 17:41 ` Jeff King
2017-05-16 17:21 ` Eric Rannaud
2017-05-16 17:37 ` Jeff King
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