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From: "Σταύρος Ντέντος" <stdedos@gmail.com>
To: Jeff King <peff@peff.net>
Cc: git <git@vger.kernel.org>
Subject: Re: Git alias syntax help
Date: Wed, 15 Jan 2020 01:13:17 +0200
Message-ID: <CAHMHMxVajKxjBweG=mps0gLwE1o8M69DvPb1iUQYgLXx0VO5AA@mail.gmail.com> (raw)
In-Reply-To: <20200114222802.GC3957260@coredump.intra.peff.net>

On Wed, 15 Jan 2020 at 00:28, Jeff King <peff@peff.net> wrote:
>
> On Tue, Jan 14, 2020 at 05:21:20PM +0200, Σταύρος Ντέντος wrote:
>
> > I am having an issue with git-aliases - specifically, the intricacies
> > involved in their syntax.
> >
> > In general, the syntax is confusing to me, especially when it is
> > _wise_ to use quotes inside a `!sh` alias.
> > e.g. which one would be the correct one
> > new = "!f() { : git log ; git log \"${1}@{1}..${1}@{0}\" \"$@\" ; } ; f"
> > new = !f() { : git log ; git log "${1}@{1}..${1}@{0}" "$@" ; } ; f
>
> Only the first one is correct. In addition to the quotes in the second
> one being eaten by the config parser, the unquoted semicolon starts a
> comment.

Could somehow the latter "become" the correct option?
Especially in the case of `!sh`:
1) You need to quote everything after `=` sign ("forced" double quotes), then
2) `sh -c` needs another set (singles are most safe here, I think), and
3) If, for some reason, you need to quote further ("$@" would be a
common suspect usually)

Apart from the [1] feeling unneeded (the equivalent of Python's
`alias_cmd = cfg_line.split()[1]` could be enough), this brings a
quoting mess on [3]

> > The alias confusing me is more specifically this:
> > https://git.wiki.kernel.org/index.php/Aliases#simple_diff_ignoring_line_number_changes
> >
> > diffsort = !sh -c 'git diff "$@" | grep "^[+-]" | sort --key=1.2 | uniq -u -s1'
> >
> > The output of:
> > $  colordiff -su <(git diffsort HEAD^..HEAD) <(git diffsort HEAD^^..HEAD^)
> > Files /dev/fd/63 and /dev/fd/62 are identical
> > is a little unexpected, since I know for a fact that one of the
> > referced commits is not a code block moved.
>
> The issue here isn't with Git's alias mechanism, but a quirk of how "sh
> -c" works.  You can run with GIT_TRACE to see what we're passing to the
> shell (though note that your double-quotes don't make it through):
>
>   $ GIT_TRACE=1 git diffsort HEAD^..HEAD
>   17:22:47.644542 [pid=3959333] git.c:708           trace: exec: git-diffsort HEAD^..HEAD
>   17:22:47.644648 [pid=3959333] run-command.c:663   trace: run_command: git-diffsort HEAD^..HEAD
>   17:22:47.645038 [pid=3959333] run-command.c:663   trace: run_command: 'sh -c '\''git diff $@ | grep ^[+-] | sort --key=1.2 | uniq -u -s1'\''' HEAD^..HEAD
>   17:22:47.650319 [pid=3959336] git.c:439           trace: built-in: git diff
>
> The problem is that "sh -c" takes the first non-option argument as $0,
> not $1. For example:
>
>   $ sh -c 'echo 0=$0, @=$@' foo bar baz
>   0=foo, @=bar baz
>
> You can add any extra string there to become $0, like:
>
>   diffsort = "!sh -c 'git diff \"$@\" | grep \"^[+-]\" | sort --key=1.2 | uniq -u -s1' --"
>
> which will do what you want. You can use whatever string you like, since
> you know that your "-c" snippet does not ever look at $0.
>
> -Peff

Thank you very much for a complete explaination of all of this .

Can some of this be documented somewhere?
Are they somewhere and I missed them?

If nothing more, a link to this e-mail chain either on the wiki (if
https://git.wiki.kernel.org/index.php/Aliases is an official page) or
on git-alias help (here
https://git-scm.com/book/en/v2/Git-Basics-Git-Aliases or in some
"advanced" section, which I cannot find)

If https://git.wiki.kernel.org/index.php/Aliases is an official page,
then: was this written for an earlier version?
Could it also be updated?

--
Ntentos Stavros

  reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-14 15:21 Σταύρος Ντέντος
2020-01-14 22:28 ` Jeff King
2020-01-14 23:13   ` Σταύρος Ντέντος [this message]
2020-01-15 18:13     ` Jeff King
2020-03-28 17:05       ` Philip Oakley

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